[PATCH 0/2] yet another attempt to fix the ctime and mtime issue

[PATCH 0/2] yet another attempt to fix the ctime and mtime issue

[Anton Salikhmetov]

The POSIX standard requires that the ctime and mtime fields
for memory-mapped files should be updated after a write
reference to the memory region where the file data is mapped.
At least FreeBSD 6.2 and HP-UX 11i implement this properly.
Linux does not, which leads to data loss problems in database
backup applications.

Kernel Bug Tracker contains more information about the problem:

http://bugzilla.kernel.org/show_bug.cgi?id=2645

There have been several attempts in the past to address this
issue. Following are a few links to LKML discussions related
to this bug:

http://lkml.org/lkml/2006/5/17/138
http://lkml.org/lkml/2007/2/21/242
http://lkml.org/lkml/2008/1/7/234

All earlier solutions were criticized. Some solutions did not
handle memory-mapped block devices properly. Some led to forcing
applications to explicitly call msync() to update file metadata.
Some contained errors in using kernel synchronization primitives.

In the two patches that follow, I would like to propose a new
solution.

This is the third version of my changes. This version takes
into account all feedback I received for the two previous versions.
The overall design remains basically the same as the one that
was acked by Rick van Riel:

http://lkml.org/lkml/2008/1/11/208

To the best of my knowledge, these patches are free of all the
drawbacks found during previous attempts by Peter Staubach,
Miklos Szeredi and myself.

New since the previous version:

1) no need to explicitly call msync() to update file times;
2) changing block device data is visible to all device files
   associated with the block device;
3) in the cleanup part, the error checks are separated out as
   suggested by Rik van Riel;
4) some small refinements accodring to the LKML comments.

This is how I tested the patches.

1. To test the features mentioned above, I wrote a unit test
   available from

   http://bugzilla.kernel.org/attachment.cgi?id=14430

   I verified that the unit test passed successfully for both
   regular files and block device files. For the unit test I
   used the following architectures: 32-bit x86, x86_64 and
   MIPS32 (cross-compiled from x86_64).

2. I did build tests with allmodconfig and allyesconfig on x86_64.

3. I ran the following test cases from the LTP test suite:

   msync01
   msync02
   msync03
   msync04
   msync05
   mmapstress01
   mmapstress09
   mmapstress10

   No regressions were found by these test cases.

I think that the bug #2645 is resolved by these patches.

Please apply.

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[PATCH 1/2] massive code cleanup of sys_msync()

[Anton Salikhmetov]

Substantial code cleanup of the sys_msync() function:

1) using the PAGE_ALIGN() macro instead of "manual" alignment;
2) improved readability of the loop traversing the process memory regions.

Signed-off-by: Anton Salikhmetov <salikhmetov@gmail.com>
---
 mm/msync.c |   78 +++++++++++++++++++++++++++---------------------------------
 1 files changed, 35 insertions(+), 43 deletions(-)

diff --git a/mm/msync.c b/mm/msync.c
index 144a757..ff654c9 100644
--- a/mm/msync.c
+++ b/mm/msync.c
@@ -1,24 +1,25 @@
 /*
  *	linux/mm/msync.c
  *
+ * The msync() system call.
  * Copyright (C) 1994-1999  Linus Torvalds
+ *
+ * Substantial code cleanup.
+ * Copyright (C) 2008 Anton Salikhmetov <salikhmetov@gmail.com>
  */
 
-/*
- * The msync() system call.
- */
+#include <linux/file.h>
 #include <linux/fs.h>
 #include <linux/mm.h>
 #include <linux/mman.h>
-#include <linux/file.h>
-#include <linux/syscalls.h>
 #include <linux/sched.h>
+#include <linux/syscalls.h>
 
 /*
  * MS_SYNC syncs the entire file - including mappings.
  *
  * MS_ASYNC does not start I/O (it used to, up to 2.5.67).
- * Nor does it marks the relevant pages dirty (it used to up to 2.6.17).
+ * Nor does it mark the relevant pages dirty (it used to up to 2.6.17).
  * Now it doesn't do anything, since dirty pages are properly tracked.
  *
  * The application may now run fsync() to
@@ -33,71 +34,62 @@ asmlinkage long sys_msync(unsigned long start, size_t len, int flags)
 	unsigned long end;
 	struct mm_struct *mm = current->mm;
 	struct vm_area_struct *vma;
-	int unmapped_error = 0;
-	int error = -EINVAL;
+	int error = 0, unmapped_error = 0;
 
 	if (flags & ~(MS_ASYNC | MS_INVALIDATE | MS_SYNC))
-		goto out;
+		return -EINVAL;
 	if (start & ~PAGE_MASK)
-		goto out;
+		return -EINVAL;
 	if ((flags & MS_ASYNC) && (flags & MS_SYNC))
-		goto out;
-	error = -ENOMEM;
-	len = (len + ~PAGE_MASK) & PAGE_MASK;
+		return -EINVAL;
+
+	len = PAGE_ALIGN(len);
 	end = start + len;
 	if (end < start)
-		goto out;
-	error = 0;
+		return -ENOMEM;
 	if (end == start)
-		goto out;
+		return 0;
+
 	/*
 	 * If the interval [start,end) covers some unmapped address ranges,
 	 * just ignore them, but return -ENOMEM at the end.
 	 */
 	down_read(&mm->mmap_sem);
 	vma = find_vma(mm, start);
-	for (;;) {
+	do {
 		struct file *file;
 
-		/* Still start < end. */
-		error = -ENOMEM;
-		if (!vma)
-			goto out_unlock;
-		/* Here start < vma->vm_end. */
+		if (!vma) {
+			error = -ENOMEM;
+			break;
+		}
 		if (start < vma->vm_start) {
 			start = vma->vm_start;
-			if (start >= end)
-				goto out_unlock;
+			if (start >= end) {
+				error = -ENOMEM;
+				break;
+			}
 			unmapped_error = -ENOMEM;
 		}
-		/* Here vma->vm_start <= start < vma->vm_end. */
-		if ((flags & MS_INVALIDATE) &&
-				(vma->vm_flags & VM_LOCKED)) {
+		if ((flags & MS_INVALIDATE) && (vma->vm_flags & VM_LOCKED)) {
 			error = -EBUSY;
-			goto out_unlock;
+			break;
 		}
 		file = vma->vm_file;
-		start = vma->vm_end;
-		if ((flags & MS_SYNC) && file &&
-				(vma->vm_flags & VM_SHARED)) {
+		if ((flags & MS_SYNC) && file && (vma->vm_flags & VM_SHARED)) {
 			get_file(file);
 			up_read(&mm->mmap_sem);
 			error = do_fsync(file, 0);
 			fput(file);
-			if (error || start >= end)
-				goto out;
+			if (error)
+				return error;
 			down_read(&mm->mmap_sem);
-			vma = find_vma(mm, start);
-		} else {
-			if (start >= end) {
-				error = 0;
-				goto out_unlock;
-			}
-			vma = vma->vm_next;
 		}
-	}
-out_unlock:
+
+		start = vma->vm_end;
+		vma = vma->vm_next;
+	} while (start < end);
 	up_read(&mm->mmap_sem);
-out:
+
 	return error ? : unmapped_error;
 }
-- 
1.4.4.4

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Re: [PATCH 1/2] massive code cleanup of sys_msync()

[Rik van Riel]

On Sun, 13 Jan 2008 07:39:58 +0300
Anton Salikhmetov <salikhmetov@gmail.com> wrote:

> Substantial code cleanup of the sys_msync() function:
> 
> 1) using the PAGE_ALIGN() macro instead of "manual" alignment;
> 2) improved readability of the loop traversing the process memory regions.
> 
> Signed-off-by: Anton Salikhmetov <salikhmetov@gmail.com>

Acked-by: Rik van Riel <riel@redhat.com>


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Re: [PATCH 1/2] massive code cleanup of sys_msync()

[Miklos Szeredi]

> Substantial code cleanup of the sys_msync() function:
> 
> 1) using the PAGE_ALIGN() macro instead of "manual" alignment;
> 2) improved readability of the loop traversing the process memory regions.

Thanks for doing this.  See comments below.

> Signed-off-by: Anton Salikhmetov <salikhmetov@gmail.com>
> ---
>  mm/msync.c |   78 +++++++++++++++++++++++++++---------------------------------
>  1 files changed, 35 insertions(+), 43 deletions(-)
> 
> diff --git a/mm/msync.c b/mm/msync.c
> index 144a757..ff654c9 100644
> --- a/mm/msync.c
> +++ b/mm/msync.c
> @@ -1,24 +1,25 @@
>  /*
>   *	linux/mm/msync.c
>   *
> + * The msync() system call.
>   * Copyright (C) 1994-1999  Linus Torvalds
> + *
> + * Substantial code cleanup.
> + * Copyright (C) 2008 Anton Salikhmetov <salikhmetov@gmail.com>
>   */
>  
> -/*
> - * The msync() system call.
> - */
> +#include <linux/file.h>
>  #include <linux/fs.h>
>  #include <linux/mm.h>
>  #include <linux/mman.h>
> -#include <linux/file.h>
> -#include <linux/syscalls.h>
>  #include <linux/sched.h>
> +#include <linux/syscalls.h>
>  
>  /*
>   * MS_SYNC syncs the entire file - including mappings.
>   *
>   * MS_ASYNC does not start I/O (it used to, up to 2.5.67).
> - * Nor does it marks the relevant pages dirty (it used to up to 2.6.17).
> + * Nor does it mark the relevant pages dirty (it used to up to 2.6.17).
>   * Now it doesn't do anything, since dirty pages are properly tracked.
>   *
>   * The application may now run fsync() to
> @@ -33,71 +34,62 @@ asmlinkage long sys_msync(unsigned long start, size_t len, int flags)
>  	unsigned long end;
>  	struct mm_struct *mm = current->mm;
>  	struct vm_area_struct *vma;
> -	int unmapped_error = 0;
> -	int error = -EINVAL;
> +	int error = 0, unmapped_error = 0;
>  
>  	if (flags & ~(MS_ASYNC | MS_INVALIDATE | MS_SYNC))
> -		goto out;
> +		return -EINVAL;
>  	if (start & ~PAGE_MASK)
> -		goto out;
> +		return -EINVAL;
>  	if ((flags & MS_ASYNC) && (flags & MS_SYNC))
> -		goto out;
> -	error = -ENOMEM;
> -	len = (len + ~PAGE_MASK) & PAGE_MASK;
> +		return -EINVAL;
> +
> +	len = PAGE_ALIGN(len);
>  	end = start + len;
>  	if (end < start)
> -		goto out;
> -	error = 0;
> +		return -ENOMEM;
>  	if (end == start)
> -		goto out;
> +		return 0;
> +
>  	/*
>  	 * If the interval [start,end) covers some unmapped address ranges,
>  	 * just ignore them, but return -ENOMEM at the end.
>  	 */
>  	down_read(&mm->mmap_sem);
>  	vma = find_vma(mm, start);
> -	for (;;) {
> +	do {
>  		struct file *file;
>  
> -		/* Still start < end. */
> -		error = -ENOMEM;
> -		if (!vma)
> -			goto out_unlock;
> -		/* Here start < vma->vm_end. */
> +		if (!vma) {
> +			error = -ENOMEM;
> +			break;
> +		}
>  		if (start < vma->vm_start) {
>  			start = vma->vm_start;
> -			if (start >= end)
> -				goto out_unlock;
> +			if (start >= end) {
> +				error = -ENOMEM;
> +				break;
> +			}
>  			unmapped_error = -ENOMEM;
>  		}
> -		/* Here vma->vm_start <= start < vma->vm_end. */
> -		if ((flags & MS_INVALIDATE) &&
> -				(vma->vm_flags & VM_LOCKED)) {
> +		if ((flags & MS_INVALIDATE) && (vma->vm_flags & VM_LOCKED)) {
>  			error = -EBUSY;
> -			goto out_unlock;
> +			break;
>  		}
>  		file = vma->vm_file;
> -		start = vma->vm_end;
> -		if ((flags & MS_SYNC) && file &&
> -				(vma->vm_flags & VM_SHARED)) {
> +		if ((flags & MS_SYNC) && file && (vma->vm_flags & VM_SHARED)) {
>  			get_file(file);
>  			up_read(&mm->mmap_sem);
>  			error = do_fsync(file, 0);
>  			fput(file);
> -			if (error || start >= end)
> -				goto out;
> +			if (error)
> +				return error;
>  			down_read(&mm->mmap_sem);
> -			vma = find_vma(mm, start);

Where did this line go?  It's needed because after releasing and
reacquiring the mmap sem, the old vma may have gone away.

I suggest, that when doing such a massive cleanup, that you split it
up even further into easily understandable pieces, so such bugs cannot
creep in.

> -		} else {
> -			if (start >= end) {
> -				error = 0;
> -				goto out_unlock;
> -			}
> -			vma = vma->vm_next;
>  		}
> -	}
> -out_unlock:
> +
> +		start = vma->vm_end;
> +		vma = vma->vm_next;
> +	} while (start < end);
>  	up_read(&mm->mmap_sem);
> -out:
> +
>  	return error ? : unmapped_error;
>  }
> -- 
> 1.4.4.4

Miklos

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Re: [PATCH 1/2] massive code cleanup of sys_msync()

[Anton Salikhmetov]

2008/1/14, Miklos Szeredi <miklos@szeredi.hu>:
> > Substantial code cleanup of the sys_msync() function:
> >
> > 1) using the PAGE_ALIGN() macro instead of "manual" alignment;
> > 2) improved readability of the loop traversing the process memory regions.
>
> Thanks for doing this.  See comments below.
>
> > Signed-off-by: Anton Salikhmetov <salikhmetov@gmail.com>
> > ---
> >  mm/msync.c |   78 +++++++++++++++++++++++++++---------------------------------
> >  1 files changed, 35 insertions(+), 43 deletions(-)
> >
> > diff --git a/mm/msync.c b/mm/msync.c
> > index 144a757..ff654c9 100644
> > --- a/mm/msync.c
> > +++ b/mm/msync.c
> > @@ -1,24 +1,25 @@
> >  /*
> >   *   linux/mm/msync.c
> >   *
> > + * The msync() system call.
> >   * Copyright (C) 1994-1999  Linus Torvalds
> > + *
> > + * Substantial code cleanup.
> > + * Copyright (C) 2008 Anton Salikhmetov <salikhmetov@gmail.com>
> >   */
> >
> > -/*
> > - * The msync() system call.
> > - */
> > +#include <linux/file.h>
> >  #include <linux/fs.h>
> >  #include <linux/mm.h>
> >  #include <linux/mman.h>
> > -#include <linux/file.h>
> > -#include <linux/syscalls.h>
> >  #include <linux/sched.h>
> > +#include <linux/syscalls.h>
> >
> >  /*
> >   * MS_SYNC syncs the entire file - including mappings.
> >   *
> >   * MS_ASYNC does not start I/O (it used to, up to 2.5.67).
> > - * Nor does it marks the relevant pages dirty (it used to up to 2.6.17).
> > + * Nor does it mark the relevant pages dirty (it used to up to 2.6.17).
> >   * Now it doesn't do anything, since dirty pages are properly tracked.
> >   *
> >   * The application may now run fsync() to
> > @@ -33,71 +34,62 @@ asmlinkage long sys_msync(unsigned long start, size_t len, int flags)
> >       unsigned long end;
> >       struct mm_struct *mm = current->mm;
> >       struct vm_area_struct *vma;
> > -     int unmapped_error = 0;
> > -     int error = -EINVAL;
> > +     int error = 0, unmapped_error = 0;
> >
> >       if (flags & ~(MS_ASYNC | MS_INVALIDATE | MS_SYNC))
> > -             goto out;
> > +             return -EINVAL;
> >       if (start & ~PAGE_MASK)
> > -             goto out;
> > +             return -EINVAL;
> >       if ((flags & MS_ASYNC) && (flags & MS_SYNC))
> > -             goto out;
> > -     error = -ENOMEM;
> > -     len = (len + ~PAGE_MASK) & PAGE_MASK;
> > +             return -EINVAL;
> > +
> > +     len = PAGE_ALIGN(len);
> >       end = start + len;
> >       if (end < start)
> > -             goto out;
> > -     error = 0;
> > +             return -ENOMEM;
> >       if (end == start)
> > -             goto out;
> > +             return 0;
> > +
> >       /*
> >        * If the interval [start,end) covers some unmapped address ranges,
> >        * just ignore them, but return -ENOMEM at the end.
> >        */
> >       down_read(&mm->mmap_sem);
> >       vma = find_vma(mm, start);
> > -     for (;;) {
> > +     do {
> >               struct file *file;
> >
> > -             /* Still start < end. */
> > -             error = -ENOMEM;
> > -             if (!vma)
> > -                     goto out_unlock;
> > -             /* Here start < vma->vm_end. */
> > +             if (!vma) {
> > +                     error = -ENOMEM;
> > +                     break;
> > +             }
> >               if (start < vma->vm_start) {
> >                       start = vma->vm_start;
> > -                     if (start >= end)
> > -                             goto out_unlock;
> > +                     if (start >= end) {
> > +                             error = -ENOMEM;
> > +                             break;
> > +                     }
> >                       unmapped_error = -ENOMEM;
> >               }
> > -             /* Here vma->vm_start <= start < vma->vm_end. */
> > -             if ((flags & MS_INVALIDATE) &&
> > -                             (vma->vm_flags & VM_LOCKED)) {
> > +             if ((flags & MS_INVALIDATE) && (vma->vm_flags & VM_LOCKED)) {
> >                       error = -EBUSY;
> > -                     goto out_unlock;
> > +                     break;
> >               }
> >               file = vma->vm_file;
> > -             start = vma->vm_end;
> > -             if ((flags & MS_SYNC) && file &&
> > -                             (vma->vm_flags & VM_SHARED)) {
> > +             if ((flags & MS_SYNC) && file && (vma->vm_flags & VM_SHARED)) {
> >                       get_file(file);
> >                       up_read(&mm->mmap_sem);
> >                       error = do_fsync(file, 0);
> >                       fput(file);
> > -                     if (error || start >= end)
> > -                             goto out;
> > +                     if (error)
> > +                             return error;
> >                       down_read(&mm->mmap_sem);
> > -                     vma = find_vma(mm, start);
>
> Where did this line go?  It's needed because after releasing and
> reacquiring the mmap sem, the old vma may have gone away.
>
> I suggest, that when doing such a massive cleanup, that you split it
> up even further into easily understandable pieces, so such bugs cannot
> creep in.

Thanks for your review. I overlooked this problem. I'll redo my cleanup soon.

>
> > -             } else {
> > -                     if (start >= end) {
> > -                             error = 0;
> > -                             goto out_unlock;
> > -                     }
> > -                     vma = vma->vm_next;
> >               }
> > -     }
> > -out_unlock:
> > +
> > +             start = vma->vm_end;
> > +             vma = vma->vm_next;
> > +     } while (start < end);
> >       up_read(&mm->mmap_sem);
> > -out:
> > +
> >       return error ? : unmapped_error;
> >  }
> > --
> > 1.4.4.4
>
> Miklos
>

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[PATCH 2/2] updating ctime and mtime at syncing

[Anton Salikhmetov]

Changes for updating the ctime and mtime fields for memory-mapped files:

1) new flag triggering update of the inode data;
2) new function to update ctime and mtime for block device files;
3) new helper function to update ctime and mtime when needed;
4) updating time stamps for mapped files in sys_msync() and do_fsync();
5) implementing the feature of auto-updating ctime and mtime.

Signed-off-by: Anton Salikhmetov <salikhmetov@gmail.com>
---
 fs/buffer.c             |    1 +
 fs/fs-writeback.c       |    2 ++
 fs/inode.c              |   42 +++++++++++++++++++++++++++++++++++-------
 fs/sync.c               |    2 ++
 include/linux/fs.h      |    9 ++++++++-
 include/linux/pagemap.h |    3 ++-
 mm/msync.c              |   24 ++++++++++++++++--------
 mm/page-writeback.c     |    1 +
 8 files changed, 67 insertions(+), 17 deletions(-)

diff --git a/fs/buffer.c b/fs/buffer.c
index 7249e01..09adf7e 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -719,6 +719,7 @@ static int __set_page_dirty(struct page *page,
 	}
 	write_unlock_irq(&mapping->tree_lock);
 	__mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
+	set_bit(AS_MCTIME, &mapping->flags);
 
 	return 1;
 }
diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 0fca820..c25ebd5 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -243,6 +243,8 @@ __sync_single_inode(struct inode *inode, struct writeback_control *wbc)
 
 	spin_unlock(&inode_lock);
 
+	mapping_update_time(mapping);
+
 	ret = do_writepages(mapping, wbc);
 
 	/* Don't write the inode if only I_DIRTY_PAGES was set */
diff --git a/fs/inode.c b/fs/inode.c
index ed35383..c02bfab 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -1243,8 +1243,8 @@ void touch_atime(struct vfsmount *mnt, struct dentry *dentry)
 EXPORT_SYMBOL(touch_atime);
 
 /**
- *	file_update_time	-	update mtime and ctime time
- *	@file: file accessed
+ *	inode_update_time	-	update mtime and ctime time
+ *	@inode: inode accessed
  *
  *	Update the mtime and ctime members of an inode and mark the inode
  *	for writeback.  Note that this function is meant exclusively for
@@ -1253,10 +1253,8 @@ EXPORT_SYMBOL(touch_atime);
  *	S_NOCTIME inode flag, e.g. for network filesystem where these
  *	timestamps are handled by the server.
  */
-
-void file_update_time(struct file *file)
+void inode_update_time(struct inode *inode)
 {
-	struct inode *inode = file->f_path.dentry->d_inode;
 	struct timespec now;
 	int sync_it = 0;
 
@@ -1279,8 +1277,39 @@ void file_update_time(struct file *file)
 	if (sync_it)
 		mark_inode_dirty_sync(inode);
 }
+EXPORT_SYMBOL(inode_update_time);
+
+/*
+ * Update the ctime and mtime stamps for memory-mapped block device files.
+ */
+static void bd_inode_update_time(struct inode *inode)
+{
+	struct block_device *bdev = inode->i_bdev;
+	struct list_head *p;
+
+	if (bdev == NULL)
+		return;
+
+	mutex_lock(&bdev->bd_mutex);
+	list_for_each(p, &bdev->bd_inodes) {
+		inode = list_entry(p, struct inode, i_devices);
+		inode_update_time(inode);
+	}
+	mutex_unlock(&bdev->bd_mutex);
+}
 
-EXPORT_SYMBOL(file_update_time);
+/*
+ * Update the ctime and mtime stamps after checking if they are to be updated.
+ */
+void mapping_update_time(struct address_space *mapping)
+{
+	if (test_and_clear_bit(AS_MCTIME, &mapping->flags)) {
+		if (S_ISBLK(mapping->host->i_mode))
+			bd_inode_update_time(mapping->host);
+		else
+			inode_update_time(mapping->host);
+	}
+}
 
 int inode_needs_sync(struct inode *inode)
 {
@@ -1290,7 +1319,6 @@ int inode_needs_sync(struct inode *inode)
 		return 1;
 	return 0;
 }
-
 EXPORT_SYMBOL(inode_needs_sync);
 
 int inode_wait(void *word)
diff --git a/fs/sync.c b/fs/sync.c
index 7cd005e..5561464 100644
--- a/fs/sync.c
+++ b/fs/sync.c
@@ -87,6 +87,8 @@ long do_fsync(struct file *file, int datasync)
 		goto out;
 	}
 
+	mapping_update_time(mapping);
+
 	ret = filemap_fdatawrite(mapping);
 
 	/*
diff --git a/include/linux/fs.h b/include/linux/fs.h
index b3ec4a4..1dccd4b 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1977,7 +1977,14 @@ extern int buffer_migrate_page(struct address_space *,
 extern int inode_change_ok(struct inode *, struct iattr *);
 extern int __must_check inode_setattr(struct inode *, struct iattr *);
 
-extern void file_update_time(struct file *file);
+extern void inode_update_time(struct inode *);
+
+static inline void file_update_time(struct file *file)
+{
+	inode_update_time(file->f_path.dentry->d_inode);
+}
+
+extern void mapping_update_time(struct address_space *);
 
 static inline ino_t parent_ino(struct dentry *dentry)
 {
diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index db8a410..bf0f9e7 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -17,8 +17,9 @@
  * Bits in mapping->flags.  The lower __GFP_BITS_SHIFT bits are the page
  * allocation mode flags.
  */
-#define	AS_EIO		(__GFP_BITS_SHIFT + 0)	/* IO error on async write */
+#define AS_EIO		(__GFP_BITS_SHIFT + 0)	/* IO error on async write */
 #define AS_ENOSPC	(__GFP_BITS_SHIFT + 1)	/* ENOSPC on async write */
+#define AS_MCTIME	(__GFP_BITS_SHIFT + 2)	/* mtime and ctime to update */
 
 static inline void mapping_set_error(struct address_space *mapping, int error)
 {
diff --git a/mm/msync.c b/mm/msync.c
index ff654c9..07dc8fc 100644
--- a/mm/msync.c
+++ b/mm/msync.c
@@ -5,6 +5,7 @@
  * Copyright (C) 1994-1999  Linus Torvalds
  *
  * Substantial code cleanup.
+ * Updating the ctime and mtime stamps for memory-mapped files.
  * Copyright (C) 2008 Anton Salikhmetov <salikhmetov@gmail.com>
  */
 
@@ -22,6 +23,10 @@
  * Nor does it mark the relevant pages dirty (it used to up to 2.6.17).
  * Now it doesn't do anything, since dirty pages are properly tracked.
  *
+ * The msync() system call updates the ctime and mtime fields for
+ * the mapped file when called with the MS_SYNC or MS_ASYNC flags
+ * according to the POSIX standard.
+ *
  * The application may now run fsync() to
  * write out the dirty pages and wait on the writeout and check the result.
  * Or the application may run fadvise(FADV_DONTNEED) against the fd to start
@@ -76,14 +81,17 @@ asmlinkage long sys_msync(unsigned long start, size_t len, int flags)
 			break;
 		}
 		file = vma->vm_file;
-		if ((flags & MS_SYNC) && file && (vma->vm_flags & VM_SHARED)) {
-			get_file(file);
-			up_read(&mm->mmap_sem);
-			error = do_fsync(file, 0);
-			fput(file);
-			if (error)
-				return error;
-			down_read(&mm->mmap_sem);
+		if (file && (vma->vm_flags & VM_SHARED)) {
+			mapping_update_time(file->f_mapping);
+			if (flags & MS_SYNC) {
+				get_file(file);
+				up_read(&mm->mmap_sem);
+				error = do_fsync(file, 0);
+				fput(file);
+				if (error)
+					return error;
+				down_read(&mm->mmap_sem);
+			}
 		}
 
 		start = vma->vm_end;
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index d55cfca..a85df0b 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -1025,6 +1025,7 @@ int __set_page_dirty_nobuffers(struct page *page)
 		if (mapping->host) {
 			/* !PageAnon && !swapper_space */
 			__mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
+			set_bit(AS_MCTIME, &mapping->flags);
 		}
 		return 1;
 	}
-- 
1.4.4.4

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Re: [PATCH 2/2] updating ctime and mtime at syncing

[Rik van Riel]

On Sun, 13 Jan 2008 07:39:59 +0300
Anton Salikhmetov <salikhmetov@gmail.com> wrote:

> http://bugzilla.kernel.org/show_bug.cgi?id=2645
> 
> Changes for updating the ctime and mtime fields for memory-mapped files:
> 
> 1) new flag triggering update of the inode data;
> 2) new function to update ctime and mtime for block device files;
> 3) new helper function to update ctime and mtime when needed;
> 4) updating time stamps for mapped files in sys_msync() and do_fsync();
> 5) implementing the feature of auto-updating ctime and mtime.
> 
> Signed-off-by: Anton Salikhmetov <salikhmetov@gmail.com>

Acked-by: Rik van Riel <riel@redhat.com>

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Re: [PATCH 2/2] updating ctime and mtime at syncing

[Miklos Szeredi]

> http://bugzilla.kernel.org/show_bug.cgi?id=2645
> 
> Changes for updating the ctime and mtime fields for memory-mapped files:
> 
> 1) new flag triggering update of the inode data;
> 2) new function to update ctime and mtime for block device files;
> 3) new helper function to update ctime and mtime when needed;
> 4) updating time stamps for mapped files in sys_msync() and do_fsync();
> 5) implementing the feature of auto-updating ctime and mtime.

How exactly is this done?

Is this catering for this case:

 1 page is dirtied through mapping
 2 app calls msync(MS_ASYNC)
 3 page is written again through mapping
 4 app calls msync(MS_ASYNC)
 5 ...
 6 page is written back

What happens at 4?  Do we care about this one at all?

More comments inline.

> Signed-off-by: Anton Salikhmetov <salikhmetov@gmail.com>
> ---
>  fs/buffer.c             |    1 +
>  fs/fs-writeback.c       |    2 ++
>  fs/inode.c              |   42 +++++++++++++++++++++++++++++++++++-------
>  fs/sync.c               |    2 ++
>  include/linux/fs.h      |    9 ++++++++-
>  include/linux/pagemap.h |    3 ++-
>  mm/msync.c              |   24 ++++++++++++++++--------
>  mm/page-writeback.c     |    1 +
>  8 files changed, 67 insertions(+), 17 deletions(-)
> 
> diff --git a/fs/buffer.c b/fs/buffer.c
> index 7249e01..09adf7e 100644
> --- a/fs/buffer.c
> +++ b/fs/buffer.c
> @@ -719,6 +719,7 @@ static int __set_page_dirty(struct page *page,
>  	}
>  	write_unlock_irq(&mapping->tree_lock);
>  	__mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
> +	set_bit(AS_MCTIME, &mapping->flags);
>  
>  	return 1;
>  }
> diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
> index 0fca820..c25ebd5 100644
> --- a/fs/fs-writeback.c
> +++ b/fs/fs-writeback.c
> @@ -243,6 +243,8 @@ __sync_single_inode(struct inode *inode, struct writeback_control *wbc)
>  
>  	spin_unlock(&inode_lock);
>  
> +	mapping_update_time(mapping);
> +
>  	ret = do_writepages(mapping, wbc);
>  
>  	/* Don't write the inode if only I_DIRTY_PAGES was set */
> diff --git a/fs/inode.c b/fs/inode.c
> index ed35383..c02bfab 100644
> --- a/fs/inode.c
> +++ b/fs/inode.c
> @@ -1243,8 +1243,8 @@ void touch_atime(struct vfsmount *mnt, struct dentry *dentry)
>  EXPORT_SYMBOL(touch_atime);
>  
>  /**
> - *	file_update_time	-	update mtime and ctime time
> - *	@file: file accessed
> + *	inode_update_time	-	update mtime and ctime time
> + *	@inode: inode accessed
>   *
>   *	Update the mtime and ctime members of an inode and mark the inode
>   *	for writeback.  Note that this function is meant exclusively for
> @@ -1253,10 +1253,8 @@ EXPORT_SYMBOL(touch_atime);
>   *	S_NOCTIME inode flag, e.g. for network filesystem where these
>   *	timestamps are handled by the server.
>   */
> -
> -void file_update_time(struct file *file)
> +void inode_update_time(struct inode *inode)
>  {
> -	struct inode *inode = file->f_path.dentry->d_inode;
>  	struct timespec now;
>  	int sync_it = 0;
>  
> @@ -1279,8 +1277,39 @@ void file_update_time(struct file *file)
>  	if (sync_it)
>  		mark_inode_dirty_sync(inode);
>  }
> +EXPORT_SYMBOL(inode_update_time);
> +
> +/*
> + * Update the ctime and mtime stamps for memory-mapped block device files.
> + */
> +static void bd_inode_update_time(struct inode *inode)
> +{
> +	struct block_device *bdev = inode->i_bdev;
> +	struct list_head *p;
> +
> +	if (bdev == NULL)
> +		return;
> +
> +	mutex_lock(&bdev->bd_mutex);
> +	list_for_each(p, &bdev->bd_inodes) {
> +		inode = list_entry(p, struct inode, i_devices);
> +		inode_update_time(inode);
> +	}
> +	mutex_unlock(&bdev->bd_mutex);
> +}

Umm, why not just call with file->f_dentry->d_inode, so that you don't
need to do this ugly search for the physical inode?  The file pointer
is available in both msync and fsync.

> -EXPORT_SYMBOL(file_update_time);
> +/*
> + * Update the ctime and mtime stamps after checking if they are to be updated.
> + */
> +void mapping_update_time(struct address_space *mapping)
> +{
> +	if (test_and_clear_bit(AS_MCTIME, &mapping->flags)) {
> +		if (S_ISBLK(mapping->host->i_mode))
> +			bd_inode_update_time(mapping->host);
> +		else
> +			inode_update_time(mapping->host);
> +	}
> +}
>  
>  int inode_needs_sync(struct inode *inode)
>  {
> @@ -1290,7 +1319,6 @@ int inode_needs_sync(struct inode *inode)
>  		return 1;
>  	return 0;
>  }
> -
>  EXPORT_SYMBOL(inode_needs_sync);
>  
>  int inode_wait(void *word)
> diff --git a/fs/sync.c b/fs/sync.c
> index 7cd005e..5561464 100644
> --- a/fs/sync.c
> +++ b/fs/sync.c
> @@ -87,6 +87,8 @@ long do_fsync(struct file *file, int datasync)
>  		goto out;
>  	}
>  
> +	mapping_update_time(mapping);
> +
>  	ret = filemap_fdatawrite(mapping);
>  
>  	/*
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index b3ec4a4..1dccd4b 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -1977,7 +1977,14 @@ extern int buffer_migrate_page(struct address_space *,
>  extern int inode_change_ok(struct inode *, struct iattr *);
>  extern int __must_check inode_setattr(struct inode *, struct iattr *);
>  
> -extern void file_update_time(struct file *file);
> +extern void inode_update_time(struct inode *);
> +
> +static inline void file_update_time(struct file *file)
> +{
> +	inode_update_time(file->f_path.dentry->d_inode);
> +}
> +
> +extern void mapping_update_time(struct address_space *);
>  
>  static inline ino_t parent_ino(struct dentry *dentry)
>  {
> diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
> index db8a410..bf0f9e7 100644
> --- a/include/linux/pagemap.h
> +++ b/include/linux/pagemap.h
> @@ -17,8 +17,9 @@
>   * Bits in mapping->flags.  The lower __GFP_BITS_SHIFT bits are the page
>   * allocation mode flags.
>   */
> -#define	AS_EIO		(__GFP_BITS_SHIFT + 0)	/* IO error on async write */
> +#define AS_EIO		(__GFP_BITS_SHIFT + 0)	/* IO error on async write */
>  #define AS_ENOSPC	(__GFP_BITS_SHIFT + 1)	/* ENOSPC on async write */
> +#define AS_MCTIME	(__GFP_BITS_SHIFT + 2)	/* mtime and ctime to update */
>  
>  static inline void mapping_set_error(struct address_space *mapping, int error)
>  {
> diff --git a/mm/msync.c b/mm/msync.c
> index ff654c9..07dc8fc 100644
> --- a/mm/msync.c
> +++ b/mm/msync.c
> @@ -5,6 +5,7 @@
>   * Copyright (C) 1994-1999  Linus Torvalds
>   *
>   * Substantial code cleanup.
> + * Updating the ctime and mtime stamps for memory-mapped files.
>   * Copyright (C) 2008 Anton Salikhmetov <salikhmetov@gmail.com>
>   */
>  
> @@ -22,6 +23,10 @@
>   * Nor does it mark the relevant pages dirty (it used to up to 2.6.17).
>   * Now it doesn't do anything, since dirty pages are properly tracked.
>   *
> + * The msync() system call updates the ctime and mtime fields for
> + * the mapped file when called with the MS_SYNC or MS_ASYNC flags
> + * according to the POSIX standard.
> + *
>   * The application may now run fsync() to
>   * write out the dirty pages and wait on the writeout and check the result.
>   * Or the application may run fadvise(FADV_DONTNEED) against the fd to start
> @@ -76,14 +81,17 @@ asmlinkage long sys_msync(unsigned long start, size_t len, int flags)
>  			break;
>  		}
>  		file = vma->vm_file;
> -		if ((flags & MS_SYNC) && file && (vma->vm_flags & VM_SHARED)) {
> -			get_file(file);
> -			up_read(&mm->mmap_sem);
> -			error = do_fsync(file, 0);
> -			fput(file);
> -			if (error)
> -				return error;
> -			down_read(&mm->mmap_sem);
> +		if (file && (vma->vm_flags & VM_SHARED)) {
> +			mapping_update_time(file->f_mapping);
> +			if (flags & MS_SYNC) {
> +				get_file(file);
> +				up_read(&mm->mmap_sem);
> +				error = do_fsync(file, 0);
> +				fput(file);
> +				if (error)
> +					return error;
> +				down_read(&mm->mmap_sem);
> +			}
>  		}
>  
>  		start = vma->vm_end;
> diff --git a/mm/page-writeback.c b/mm/page-writeback.c
> index d55cfca..a85df0b 100644
> --- a/mm/page-writeback.c
> +++ b/mm/page-writeback.c
> @@ -1025,6 +1025,7 @@ int __set_page_dirty_nobuffers(struct page *page)
>  		if (mapping->host) {
>  			/* !PageAnon && !swapper_space */
>  			__mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
> +			set_bit(AS_MCTIME, &mapping->flags);
>  		}
>  		return 1;
>  	}
> -- 
> 1.4.4.4

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Re: [PATCH 2/2] updating ctime and mtime at syncing

[Miklos Szeredi]

> > http://bugzilla.kernel.org/show_bug.cgi?id=2645
> > 
> > Changes for updating the ctime and mtime fields for memory-mapped files:
> > 
> > 1) new flag triggering update of the inode data;
> > 2) new function to update ctime and mtime for block device files;
> > 3) new helper function to update ctime and mtime when needed;
> > 4) updating time stamps for mapped files in sys_msync() and do_fsync();
> > 5) implementing the feature of auto-updating ctime and mtime.
> 
> How exactly is this done?
> 
> Is this catering for this case:
> 
>  1 page is dirtied through mapping
>  2 app calls msync(MS_ASYNC)
>  3 page is written again through mapping
>  4 app calls msync(MS_ASYNC)
>  5 ...
>  6 page is written back
> 
> What happens at 4?  Do we care about this one at all?

Oh, and here's a test program I wrote, that can be used to check this
behavior.   It has two options:

 -s   use MS_SYNC instead of MS_ASYNC
 -f   fork and do the msync on a different mapping

Back then I haven't found a single OS, that fully conformed to all the
stupid POSIX rules regarding mmaps and ctime/mtime.

Miklos
----

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <fcntl.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <sys/wait.h>

static const char *filename;
static int msync_flag = MS_ASYNC;
static int msync_fork = 0;

static void print_times(const char *msg)
{
    struct stat stbuf;
    stat(filename, &stbuf);
    printf("%s\t%li\t%li\t%li\n", msg, stbuf.st_ctime, stbuf.st_mtime,
           stbuf.st_atime);
}

static void do_msync(void *addr, int len)
{
    int res;
    if (!msync_fork) {
        res = msync(addr, len, msync_flag);
        if (res == -1) {
            perror("msync");
            exit(1);
        }
    } else {
        int pid = fork();
        if (pid == -1) {
            perror("fork");
            exit(1);
        }
        if (!pid) {
            int fd = open(filename, O_RDWR);
            if (fd == -1) {
                perror("open");
                exit(1);
            }
            addr = mmap(NULL, 4096, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
            if (addr == MAP_FAILED) {
                perror("mmap");
                exit(1);
            }
            res = msync(addr, len, msync_flag);
            if (res == -1) {
                perror("msync");
                exit(1);
            }
            exit(0);
        }
        wait(NULL);
    }
}

static void usage(const char *progname)
{
    fprintf(stderr, "usage: %s filename [-sf]\n", progname);
    exit(1);
}

int main(int argc, char *argv[])
{
    int res;
    char *addr;
    int fd;

    if (argc < 2)
        usage(argv[0]);

    filename = argv[1];
    if (argc > 2) {
        if (argc > 3)
            usage(argv[0]);
        if (strcmp(argv[2], "-s") == 0)
            msync_flag = MS_SYNC;
        else if (strcmp(argv[2], "-f") == 0)
            msync_fork = 1;
        else if (strcmp(argv[2], "-sf") == 0 || strcmp(argv[2], "-fs") == 0) {
            msync_flag = MS_SYNC;
            msync_fork = 1;
        } else
            usage(argv[0]);
    }

    fd = open(filename, O_RDWR | O_TRUNC | O_CREAT, 0666);
    if (fd == -1) {
        perror(filename);
        return 1;
    }
    print_times("begin");
    sleep(1);
    write(fd, "aaaa\n", 4);
    print_times("write");
    sleep(1);
    addr = mmap(NULL, 4096, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
    if (addr == MAP_FAILED) {
        perror("mmap");
        return 1;
    }
    print_times("mmap");
    sleep(1);

    addr[1] = 'b';
    print_times("b");
    sleep(1);
    do_msync(addr, 4);
    print_times("msync b");
    sleep(1);

    addr[2] = 'c';
    print_times("c");
    sleep(1);
    do_msync(addr, 4);
    print_times("msync c");
    sleep(1);

    addr[3] = 'd';
    print_times("d");
    sleep(1);
    res = munmap(addr, 4);
    if (res == -1) {
        perror("munmap");
        return 1;
    }
    print_times("munmap");
    sleep(1);

    res = close(fd);
    if (res == -1) {
        perror("close");
        return 1;
    }
    print_times("close");
    sleep(1);
    sync();
    print_times("sync");

    return 0;
}


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Re: [PATCH 2/2] updating ctime and mtime at syncing

[Anton Salikhmetov]

2008/1/14, Miklos Szeredi <miklos@szeredi.hu>:
> > > http://bugzilla.kernel.org/show_bug.cgi?id=2645
> > >
> > > Changes for updating the ctime and mtime fields for memory-mapped files:
> > >
> > > 1) new flag triggering update of the inode data;
> > > 2) new function to update ctime and mtime for block device files;
> > > 3) new helper function to update ctime and mtime when needed;
> > > 4) updating time stamps for mapped files in sys_msync() and do_fsync();
> > > 5) implementing the feature of auto-updating ctime and mtime.
> >
> > How exactly is this done?
> >
> > Is this catering for this case:
> >
> >  1 page is dirtied through mapping
> >  2 app calls msync(MS_ASYNC)
> >  3 page is written again through mapping
> >  4 app calls msync(MS_ASYNC)
> >  5 ...
> >  6 page is written back
> >
> > What happens at 4?  Do we care about this one at all?
>
> Oh, and here's a test program I wrote, that can be used to check this
> behavior.   It has two options:
>
>  -s   use MS_SYNC instead of MS_ASYNC
>  -f   fork and do the msync on a different mapping
>
> Back then I haven't found a single OS, that fully conformed to all the
> stupid POSIX rules regarding mmaps and ctime/mtime.

Thank you very much for sharing your code.

I'll integrate the MS_ASYNC and fork() test cases into my own unit test.

>
> Miklos
> ----
>
> #include <stdio.h>
> #include <stdlib.h>
> #include <unistd.h>
> #include <string.h>
> #include <fcntl.h>
> #include <sys/mman.h>
> #include <sys/stat.h>
> #include <sys/wait.h>
>
> static const char *filename;
> static int msync_flag = MS_ASYNC;
> static int msync_fork = 0;
>
> static void print_times(const char *msg)
> {
>     struct stat stbuf;
>     stat(filename, &stbuf);
>     printf("%s\t%li\t%li\t%li\n", msg, stbuf.st_ctime, stbuf.st_mtime,
>            stbuf.st_atime);
> }
>
> static void do_msync(void *addr, int len)
> {
>     int res;
>     if (!msync_fork) {
>         res = msync(addr, len, msync_flag);
>         if (res == -1) {
>             perror("msync");
>             exit(1);
>         }
>     } else {
>         int pid = fork();
>         if (pid == -1) {
>             perror("fork");
>             exit(1);
>         }
>         if (!pid) {
>             int fd = open(filename, O_RDWR);
>             if (fd == -1) {
>                 perror("open");
>                 exit(1);
>             }
>             addr = mmap(NULL, 4096, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
>             if (addr == MAP_FAILED) {
>                 perror("mmap");
>                 exit(1);
>             }
>             res = msync(addr, len, msync_flag);
>             if (res == -1) {
>                 perror("msync");
>                 exit(1);
>             }
>             exit(0);
>         }
>         wait(NULL);
>     }
> }
>
> static void usage(const char *progname)
> {
>     fprintf(stderr, "usage: %s filename [-sf]\n", progname);
>     exit(1);
> }
>
> int main(int argc, char *argv[])
> {
>     int res;
>     char *addr;
>     int fd;
>
>     if (argc < 2)
>         usage(argv[0]);
>
>     filename = argv[1];
>     if (argc > 2) {
>         if (argc > 3)
>             usage(argv[0]);
>         if (strcmp(argv[2], "-s") == 0)
>             msync_flag = MS_SYNC;
>         else if (strcmp(argv[2], "-f") == 0)
>             msync_fork = 1;
>         else if (strcmp(argv[2], "-sf") == 0 || strcmp(argv[2], "-fs") == 0) {
>             msync_flag = MS_SYNC;
>             msync_fork = 1;
>         } else
>             usage(argv[0]);
>     }
>
>     fd = open(filename, O_RDWR | O_TRUNC | O_CREAT, 0666);
>     if (fd == -1) {
>         perror(filename);
>         return 1;
>     }
>     print_times("begin");
>     sleep(1);
>     write(fd, "aaaa\n", 4);
>     print_times("write");
>     sleep(1);
>     addr = mmap(NULL, 4096, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
>     if (addr == MAP_FAILED) {
>         perror("mmap");
>         return 1;
>     }
>     print_times("mmap");
>     sleep(1);
>
>     addr[1] = 'b';
>     print_times("b");
>     sleep(1);
>     do_msync(addr, 4);
>     print_times("msync b");
>     sleep(1);
>
>     addr[2] = 'c';
>     print_times("c");
>     sleep(1);
>     do_msync(addr, 4);
>     print_times("msync c");
>     sleep(1);
>
>     addr[3] = 'd';
>     print_times("d");
>     sleep(1);
>     res = munmap(addr, 4);
>     if (res == -1) {
>         perror("munmap");
>         return 1;
>     }
>     print_times("munmap");
>     sleep(1);
>
>     res = close(fd);
>     if (res == -1) {
>         perror("close");
>         return 1;
>     }
>     print_times("close");
>     sleep(1);
>     sync();
>     print_times("sync");
>
>     return 0;
> }
>
>
>

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Re: [PATCH 2/2] updating ctime and mtime at syncing

[Anton Salikhmetov]

2008/1/14, Miklos Szeredi <miklos@szeredi.hu>:
> > http://bugzilla.kernel.org/show_bug.cgi?id=2645
> >
> > Changes for updating the ctime and mtime fields for memory-mapped files:
> >
> > 1) new flag triggering update of the inode data;
> > 2) new function to update ctime and mtime for block device files;
> > 3) new helper function to update ctime and mtime when needed;
> > 4) updating time stamps for mapped files in sys_msync() and do_fsync();
> > 5) implementing the feature of auto-updating ctime and mtime.
>
> How exactly is this done?
>
> Is this catering for this case:
>
>  1 page is dirtied through mapping
>  2 app calls msync(MS_ASYNC)
>  3 page is written again through mapping
>  4 app calls msync(MS_ASYNC)
>  5 ...
>  6 page is written back
>
> What happens at 4?  Do we care about this one at all?

The POSIX standard requires updating the file times every time when msync()
is called with MS_ASYNC. I.e. the time stamps should be updated even
when no physical synchronization is being done immediately.

At least, this is how I undestand the standard. Please tell me if I am wrong.

>
> More comments inline.
>
> > Signed-off-by: Anton Salikhmetov <salikhmetov@gmail.com>
> > ---
> >  fs/buffer.c             |    1 +
> >  fs/fs-writeback.c       |    2 ++
> >  fs/inode.c              |   42 +++++++++++++++++++++++++++++++++++-------
> >  fs/sync.c               |    2 ++
> >  include/linux/fs.h      |    9 ++++++++-
> >  include/linux/pagemap.h |    3 ++-
> >  mm/msync.c              |   24 ++++++++++++++++--------
> >  mm/page-writeback.c     |    1 +
> >  8 files changed, 67 insertions(+), 17 deletions(-)
> >
> > diff --git a/fs/buffer.c b/fs/buffer.c
> > index 7249e01..09adf7e 100644
> > --- a/fs/buffer.c
> > +++ b/fs/buffer.c
> > @@ -719,6 +719,7 @@ static int __set_page_dirty(struct page *page,
> >       }
> >       write_unlock_irq(&mapping->tree_lock);
> >       __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
> > +     set_bit(AS_MCTIME, &mapping->flags);
> >
> >       return 1;
> >  }
> > diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
> > index 0fca820..c25ebd5 100644
> > --- a/fs/fs-writeback.c
> > +++ b/fs/fs-writeback.c
> > @@ -243,6 +243,8 @@ __sync_single_inode(struct inode *inode, struct writeback_control *wbc)
> >
> >       spin_unlock(&inode_lock);
> >
> > +     mapping_update_time(mapping);
> > +
> >       ret = do_writepages(mapping, wbc);
> >
> >       /* Don't write the inode if only I_DIRTY_PAGES was set */
> > diff --git a/fs/inode.c b/fs/inode.c
> > index ed35383..c02bfab 100644
> > --- a/fs/inode.c
> > +++ b/fs/inode.c
> > @@ -1243,8 +1243,8 @@ void touch_atime(struct vfsmount *mnt, struct dentry *dentry)
> >  EXPORT_SYMBOL(touch_atime);
> >
> >  /**
> > - *   file_update_time        -       update mtime and ctime time
> > - *   @file: file accessed
> > + *   inode_update_time       -       update mtime and ctime time
> > + *   @inode: inode accessed
> >   *
> >   *   Update the mtime and ctime members of an inode and mark the inode
> >   *   for writeback.  Note that this function is meant exclusively for
> > @@ -1253,10 +1253,8 @@ EXPORT_SYMBOL(touch_atime);
> >   *   S_NOCTIME inode flag, e.g. for network filesystem where these
> >   *   timestamps are handled by the server.
> >   */
> > -
> > -void file_update_time(struct file *file)
> > +void inode_update_time(struct inode *inode)
> >  {
> > -     struct inode *inode = file->f_path.dentry->d_inode;
> >       struct timespec now;
> >       int sync_it = 0;
> >
> > @@ -1279,8 +1277,39 @@ void file_update_time(struct file *file)
> >       if (sync_it)
> >               mark_inode_dirty_sync(inode);
> >  }
> > +EXPORT_SYMBOL(inode_update_time);
> > +
> > +/*
> > + * Update the ctime and mtime stamps for memory-mapped block device files.
> > + */
> > +static void bd_inode_update_time(struct inode *inode)
> > +{
> > +     struct block_device *bdev = inode->i_bdev;
> > +     struct list_head *p;
> > +
> > +     if (bdev == NULL)
> > +             return;
> > +
> > +     mutex_lock(&bdev->bd_mutex);
> > +     list_for_each(p, &bdev->bd_inodes) {
> > +             inode = list_entry(p, struct inode, i_devices);
> > +             inode_update_time(inode);
> > +     }
> > +     mutex_unlock(&bdev->bd_mutex);
> > +}
>
> Umm, why not just call with file->f_dentry->d_inode, so that you don't
> need to do this ugly search for the physical inode?  The file pointer
> is available in both msync and fsync.

I'm not sure if I undestood your question. I see two possible
interpretations for this
question, and I'm answering both.

The intention was to make the data changes in the block device data visible to
all device files associated with the block device. Hence the search,
because the time
stamps for all such device files should be updated as well.

Not only the sys_msync() and do_fsync() routines call the helper function
mapping_update_time(). Not all call sites of the helper function have the file
pointer available. Therefore, I pass the mapping pointer to the helper function
in order to make this function adequate for all situations.

>
> > -EXPORT_SYMBOL(file_update_time);
> > +/*
> > + * Update the ctime and mtime stamps after checking if they are to be updated.
> > + */
> > +void mapping_update_time(struct address_space *mapping)
> > +{
> > +     if (test_and_clear_bit(AS_MCTIME, &mapping->flags)) {
> > +             if (S_ISBLK(mapping->host->i_mode))
> > +                     bd_inode_update_time(mapping->host);
> > +             else
> > +                     inode_update_time(mapping->host);
> > +     }
> > +}
> >
> >  int inode_needs_sync(struct inode *inode)
> >  {
> > @@ -1290,7 +1319,6 @@ int inode_needs_sync(struct inode *inode)
> >               return 1;
> >       return 0;
> >  }
> > -
> >  EXPORT_SYMBOL(inode_needs_sync);
> >
> >  int inode_wait(void *word)
> > diff --git a/fs/sync.c b/fs/sync.c
> > index 7cd005e..5561464 100644
> > --- a/fs/sync.c
> > +++ b/fs/sync.c
> > @@ -87,6 +87,8 @@ long do_fsync(struct file *file, int datasync)
> >               goto out;
> >       }
> >
> > +     mapping_update_time(mapping);
> > +
> >       ret = filemap_fdatawrite(mapping);
> >
> >       /*
> > diff --git a/include/linux/fs.h b/include/linux/fs.h
> > index b3ec4a4..1dccd4b 100644
> > --- a/include/linux/fs.h
> > +++ b/include/linux/fs.h
> > @@ -1977,7 +1977,14 @@ extern int buffer_migrate_page(struct address_space *,
> >  extern int inode_change_ok(struct inode *, struct iattr *);
> >  extern int __must_check inode_setattr(struct inode *, struct iattr *);
> >
> > -extern void file_update_time(struct file *file);
> > +extern void inode_update_time(struct inode *);
> > +
> > +static inline void file_update_time(struct file *file)
> > +{
> > +     inode_update_time(file->f_path.dentry->d_inode);
> > +}
> > +
> > +extern void mapping_update_time(struct address_space *);
> >
> >  static inline ino_t parent_ino(struct dentry *dentry)
> >  {
> > diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
> > index db8a410..bf0f9e7 100644
> > --- a/include/linux/pagemap.h
> > +++ b/include/linux/pagemap.h
> > @@ -17,8 +17,9 @@
> >   * Bits in mapping->flags.  The lower __GFP_BITS_SHIFT bits are the page
> >   * allocation mode flags.
> >   */
> > -#define      AS_EIO          (__GFP_BITS_SHIFT + 0)  /* IO error on async write */
> > +#define AS_EIO               (__GFP_BITS_SHIFT + 0)  /* IO error on async write */
> >  #define AS_ENOSPC    (__GFP_BITS_SHIFT + 1)  /* ENOSPC on async write */
> > +#define AS_MCTIME    (__GFP_BITS_SHIFT + 2)  /* mtime and ctime to update */
> >
> >  static inline void mapping_set_error(struct address_space *mapping, int error)
> >  {
> > diff --git a/mm/msync.c b/mm/msync.c
> > index ff654c9..07dc8fc 100644
> > --- a/mm/msync.c
> > +++ b/mm/msync.c
> > @@ -5,6 +5,7 @@
> >   * Copyright (C) 1994-1999  Linus Torvalds
> >   *
> >   * Substantial code cleanup.
> > + * Updating the ctime and mtime stamps for memory-mapped files.
> >   * Copyright (C) 2008 Anton Salikhmetov <salikhmetov@gmail.com>
> >   */
> >
> > @@ -22,6 +23,10 @@
> >   * Nor does it mark the relevant pages dirty (it used to up to 2.6.17).
> >   * Now it doesn't do anything, since dirty pages are properly tracked.
> >   *
> > + * The msync() system call updates the ctime and mtime fields for
> > + * the mapped file when called with the MS_SYNC or MS_ASYNC flags
> > + * according to the POSIX standard.
> > + *
> >   * The application may now run fsync() to
> >   * write out the dirty pages and wait on the writeout and check the result.
> >   * Or the application may run fadvise(FADV_DONTNEED) against the fd to start
> > @@ -76,14 +81,17 @@ asmlinkage long sys_msync(unsigned long start, size_t len, int flags)
> >                       break;
> >               }
> >               file = vma->vm_file;
> > -             if ((flags & MS_SYNC) && file && (vma->vm_flags & VM_SHARED)) {
> > -                     get_file(file);
> > -                     up_read(&mm->mmap_sem);
> > -                     error = do_fsync(file, 0);
> > -                     fput(file);
> > -                     if (error)
> > -                             return error;
> > -                     down_read(&mm->mmap_sem);
> > +             if (file && (vma->vm_flags & VM_SHARED)) {
> > +                     mapping_update_time(file->f_mapping);
> > +                     if (flags & MS_SYNC) {
> > +                             get_file(file);
> > +                             up_read(&mm->mmap_sem);
> > +                             error = do_fsync(file, 0);
> > +                             fput(file);
> > +                             if (error)
> > +                                     return error;
> > +                             down_read(&mm->mmap_sem);
> > +                     }
> >               }
> >
> >               start = vma->vm_end;
> > diff --git a/mm/page-writeback.c b/mm/page-writeback.c
> > index d55cfca..a85df0b 100644
> > --- a/mm/page-writeback.c
> > +++ b/mm/page-writeback.c
> > @@ -1025,6 +1025,7 @@ int __set_page_dirty_nobuffers(struct page *page)
> >               if (mapping->host) {
> >                       /* !PageAnon && !swapper_space */
> >                       __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
> > +                     set_bit(AS_MCTIME, &mapping->flags);
> >               }
> >               return 1;
> >       }
> > --
> > 1.4.4.4
>

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Re: [PATCH 2/2] updating ctime and mtime at syncing

[Miklos Szeredi]

> 2008/1/14, Miklos Szeredi <miklos@szeredi.hu>:
> > > http://bugzilla.kernel.org/show_bug.cgi?id=2645
> > >
> > > Changes for updating the ctime and mtime fields for memory-mapped files:
> > >
> > > 1) new flag triggering update of the inode data;
> > > 2) new function to update ctime and mtime for block device files;
> > > 3) new helper function to update ctime and mtime when needed;
> > > 4) updating time stamps for mapped files in sys_msync() and do_fsync();
> > > 5) implementing the feature of auto-updating ctime and mtime.
> >
> > How exactly is this done?
> >
> > Is this catering for this case:
> >
> >  1 page is dirtied through mapping
> >  2 app calls msync(MS_ASYNC)
> >  3 page is written again through mapping
> >  4 app calls msync(MS_ASYNC)
> >  5 ...
> >  6 page is written back
> >
> > What happens at 4?  Do we care about this one at all?
> 
> The POSIX standard requires updating the file times every time when msync()
> is called with MS_ASYNC. I.e. the time stamps should be updated even
> when no physical synchronization is being done immediately.

Yes.  However, on linux MS_ASYNC is basically a no-op, and without
doing _something_ with the dirty pages (which afaics your patch
doesn't do), it's impossible to observe later writes to the same page.

I don't advocate full POSIX conformance anymore, because it's probably
too expensive to do (I've tried).  Rather than that, we should
probably find some sane compromise, that just fixes the real life
issue.  Here's a pointer to the thread about this:

http://lkml.org/lkml/2007/3/27/55

Your patch may be a good soultion, but you should describe in detail
what it does when pages are dirtied, and when msync/fsync are called,
and what happens with multiple msync calls that I've asked about.

I suspect your patch is ignoring writes after the first msync, but
then why care about msync at all?  What's so special about the _first_
msync?  Is it just that most test programs only check this, and not
what happens if msync is called more than once?  That would be a bug
in the test cases.

> > > +/*
> > > + * Update the ctime and mtime stamps for memory-mapped block device files.
> > > + */
> > > +static void bd_inode_update_time(struct inode *inode)
> > > +{
> > > +     struct block_device *bdev = inode->i_bdev;
> > > +     struct list_head *p;
> > > +
> > > +     if (bdev == NULL)
> > > +             return;
> > > +
> > > +     mutex_lock(&bdev->bd_mutex);
> > > +     list_for_each(p, &bdev->bd_inodes) {
> > > +             inode = list_entry(p, struct inode, i_devices);
> > > +             inode_update_time(inode);
> > > +     }
> > > +     mutex_unlock(&bdev->bd_mutex);
> > > +}
> >
> > Umm, why not just call with file->f_dentry->d_inode, so that you don't
> > need to do this ugly search for the physical inode?  The file pointer
> > is available in both msync and fsync.
> 
> I'm not sure if I undestood your question. I see two possible
> interpretations for this question, and I'm answering both.
> 
> The intention was to make the data changes in the block device data
> visible to all device files associated with the block device. Hence
> the search, because the time stamps for all such device files should
> be updated as well.

Ahh, but it will only update "active" devices, which are currently
open, no?  Is that what we want?

> Not only the sys_msync() and do_fsync() routines call the helper
> function mapping_update_time().

Ah yes, __sync_single_inode() calls it as well.  Why?

Miklos

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Re: [PATCH 2/2] updating ctime and mtime at syncing

[Peter Zijlstra]

On Mon, 2008-01-14 at 14:14 +0100, Miklos Szeredi wrote:
> > 2008/1/14, Miklos Szeredi <miklos@szeredi.hu>:
> > > > http://bugzilla.kernel.org/show_bug.cgi?id=2645
> > > >
> > > > Changes for updating the ctime and mtime fields for memory-mapped files:
> > > >
> > > > 1) new flag triggering update of the inode data;
> > > > 2) new function to update ctime and mtime for block device files;
> > > > 3) new helper function to update ctime and mtime when needed;
> > > > 4) updating time stamps for mapped files in sys_msync() and do_fsync();
> > > > 5) implementing the feature of auto-updating ctime and mtime.
> > >
> > > How exactly is this done?
> > >
> > > Is this catering for this case:
> > >
> > >  1 page is dirtied through mapping
> > >  2 app calls msync(MS_ASYNC)
> > >  3 page is written again through mapping
> > >  4 app calls msync(MS_ASYNC)
> > >  5 ...
> > >  6 page is written back
> > >
> > > What happens at 4?  Do we care about this one at all?
> > 
> > The POSIX standard requires updating the file times every time when msync()
> > is called with MS_ASYNC. I.e. the time stamps should be updated even
> > when no physical synchronization is being done immediately.
> 
> Yes.  However, on linux MS_ASYNC is basically a no-op, and without
> doing _something_ with the dirty pages (which afaics your patch
> doesn't do), it's impossible to observe later writes to the same page.
> 
> I don't advocate full POSIX conformance anymore, because it's probably
> too expensive to do (I've tried).  Rather than that, we should
> probably find some sane compromise, that just fixes the real life
> issue.  Here's a pointer to the thread about this:
> 
> http://lkml.org/lkml/2007/3/27/55
> 
> Your patch may be a good soultion, but you should describe in detail
> what it does when pages are dirtied, and when msync/fsync are called,
> and what happens with multiple msync calls that I've asked about.
> 
> I suspect your patch is ignoring writes after the first msync, but
> then why care about msync at all?  What's so special about the _first_
> msync?  Is it just that most test programs only check this, and not
> what happens if msync is called more than once?  That would be a bug
> in the test cases.

I must agree, doing the mmap dirty, MS_ASYNC, mmap retouch, MS_ASYNC
case correctly would need a lot more code which I doubt is worth the
effort.

It would require scanning the PTEs and marking them read-only again on
MS_ASYNC, and some more logic in set_page_dirty() because that currently
bails out early if the page in question is already dirty.



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Re: [PATCH 2/2] updating ctime and mtime at syncing

[Peter Zijlstra]

On Mon, 2008-01-14 at 14:35 +0100, Peter Zijlstra wrote:
> On Mon, 2008-01-14 at 14:14 +0100, Miklos Szeredi wrote:
> > > 2008/1/14, Miklos Szeredi <miklos@szeredi.hu>:
> > > > > http://bugzilla.kernel.org/show_bug.cgi?id=2645
> > > > >
> > > > > Changes for updating the ctime and mtime fields for memory-mapped files:
> > > > >
> > > > > 1) new flag triggering update of the inode data;
> > > > > 2) new function to update ctime and mtime for block device files;
> > > > > 3) new helper function to update ctime and mtime when needed;
> > > > > 4) updating time stamps for mapped files in sys_msync() and do_fsync();
> > > > > 5) implementing the feature of auto-updating ctime and mtime.
> > > >
> > > > How exactly is this done?
> > > >
> > > > Is this catering for this case:
> > > >
> > > >  1 page is dirtied through mapping
> > > >  2 app calls msync(MS_ASYNC)
> > > >  3 page is written again through mapping
> > > >  4 app calls msync(MS_ASYNC)
> > > >  5 ...
> > > >  6 page is written back
> > > >
> > > > What happens at 4?  Do we care about this one at all?
> > > 
> > > The POSIX standard requires updating the file times every time when msync()
> > > is called with MS_ASYNC. I.e. the time stamps should be updated even
> > > when no physical synchronization is being done immediately.
> > 
> > Yes.  However, on linux MS_ASYNC is basically a no-op, and without
> > doing _something_ with the dirty pages (which afaics your patch
> > doesn't do), it's impossible to observe later writes to the same page.
> > 
> > I don't advocate full POSIX conformance anymore, because it's probably
> > too expensive to do (I've tried).  Rather than that, we should
> > probably find some sane compromise, that just fixes the real life
> > issue.  Here's a pointer to the thread about this:
> > 
> > http://lkml.org/lkml/2007/3/27/55
> > 
> > Your patch may be a good soultion, but you should describe in detail
> > what it does when pages are dirtied, and when msync/fsync are called,
> > and what happens with multiple msync calls that I've asked about.
> > 
> > I suspect your patch is ignoring writes after the first msync, but
> > then why care about msync at all?  What's so special about the _first_
> > msync?  Is it just that most test programs only check this, and not
> > what happens if msync is called more than once?  That would be a bug
> > in the test cases.
> 
> I must agree, doing the mmap dirty, MS_ASYNC, mmap retouch, MS_ASYNC
> case correctly would need a lot more code which I doubt is worth the
> effort.
> 
> It would require scanning the PTEs and marking them read-only again on
> MS_ASYNC, and some more logic in set_page_dirty() because that currently
> bails out early if the page in question is already dirty.

More fun, it would require marking them RO but leaving the dirty bit
set, because this ext3 fudge where we confuse the page dirty state - or
did that get fixed?

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Re: [PATCH 2/2] updating ctime and mtime at syncing

[Miklos Szeredi]

> More fun, it would require marking them RO but leaving the dirty bit
> set, because this ext3 fudge where we confuse the page dirty state - or
> did that get fixed?

That got fixed by Nick, I think.

The alternative to marking pages RO, is to walk the PTEs in MS_ASYNC,
note the dirty bit and mark pages clean.  But it's possibly even more
complicated.

Miklos

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Re: [PATCH 2/2] updating ctime and mtime at syncing

[Miklos Szeredi]

> > More fun, it would require marking them RO but leaving the dirty bit
> > set, because this ext3 fudge where we confuse the page dirty state - or
> > did that get fixed?
> 
> That got fixed by Nick, I think.
> 
> The alternative to marking pages RO, is to walk the PTEs in MS_ASYNC,
> note the dirty bit and mark pages clean.  But it's possibly even more
                              ^^^^
			         ptes, I mean

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Re: [PATCH 2/2] updating ctime and mtime at syncing

[Anton Salikhmetov]

2008/1/14, Peter Zijlstra <a.p.zijlstra@chello.nl>:
>
> On Mon, 2008-01-14 at 14:14 +0100, Miklos Szeredi wrote:
> > > 2008/1/14, Miklos Szeredi <miklos@szeredi.hu>:
> > > > > http://bugzilla.kernel.org/show_bug.cgi?id=2645
> > > > >
> > > > > Changes for updating the ctime and mtime fields for memory-mapped files:
> > > > >
> > > > > 1) new flag triggering update of the inode data;
> > > > > 2) new function to update ctime and mtime for block device files;
> > > > > 3) new helper function to update ctime and mtime when needed;
> > > > > 4) updating time stamps for mapped files in sys_msync() and do_fsync();
> > > > > 5) implementing the feature of auto-updating ctime and mtime.
> > > >
> > > > How exactly is this done?
> > > >
> > > > Is this catering for this case:
> > > >
> > > >  1 page is dirtied through mapping
> > > >  2 app calls msync(MS_ASYNC)
> > > >  3 page is written again through mapping
> > > >  4 app calls msync(MS_ASYNC)
> > > >  5 ...
> > > >  6 page is written back
> > > >
> > > > What happens at 4?  Do we care about this one at all?
> > >
> > > The POSIX standard requires updating the file times every time when msync()
> > > is called with MS_ASYNC. I.e. the time stamps should be updated even
> > > when no physical synchronization is being done immediately.
> >
> > Yes.  However, on linux MS_ASYNC is basically a no-op, and without
> > doing _something_ with the dirty pages (which afaics your patch
> > doesn't do), it's impossible to observe later writes to the same page.
> >
> > I don't advocate full POSIX conformance anymore, because it's probably
> > too expensive to do (I've tried).  Rather than that, we should
> > probably find some sane compromise, that just fixes the real life
> > issue.  Here's a pointer to the thread about this:
> >
> > http://lkml.org/lkml/2007/3/27/55
> >
> > Your patch may be a good soultion, but you should describe in detail
> > what it does when pages are dirtied, and when msync/fsync are called,
> > and what happens with multiple msync calls that I've asked about.
> >
> > I suspect your patch is ignoring writes after the first msync, but
> > then why care about msync at all?  What's so special about the _first_
> > msync?  Is it just that most test programs only check this, and not
> > what happens if msync is called more than once?  That would be a bug
> > in the test cases.
>
> I must agree, doing the mmap dirty, MS_ASYNC, mmap retouch, MS_ASYNC
> case correctly would need a lot more code which I doubt is worth the
> effort.
>
> It would require scanning the PTEs and marking them read-only again on
> MS_ASYNC, and some more logic in set_page_dirty() because that currently
> bails out early if the page in question is already dirty.

Thanks for your review, Peter and Miklos!

I overlooked this case when AS_MCTIME flag has been turned off and the
page is still dirty.

On the other hand, the words "shall be marked for update" may be
considered as just setting the AS_MCTIME flag, not updating the time
stamps.

What do you think about calling mapping_update_time() inside of "if
(MS_SYNC & flags)"? I suggest such change because the code for
analysis of the case you've mentioned above seems impossible to me.

>
>
>
>

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Re: [PATCH 2/2] updating ctime and mtime at syncing

[Miklos Szeredi]

> Thanks for your review, Peter and Miklos!
> 
> I overlooked this case when AS_MCTIME flag has been turned off and the
> page is still dirty.
> 
> On the other hand, the words "shall be marked for update" may be
> considered as just setting the AS_MCTIME flag, not updating the time
> stamps.
> 
> What do you think about calling mapping_update_time() inside of "if
> (MS_SYNC & flags)"? I suggest such change because the code for
> analysis of the case you've mentioned above seems impossible to me.

I think that's a good idea.  As a first iteration, just updating the
mtime/ctime in msync(MS_SYNC) and remove_vma() (called at munmap time)
would be a big improvement over what we currently have.

I would also recommend, that you drop mapping_update_time() and the
related functions from the patch, and just use file_update_time()
instead.

Miklos

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Re: [PATCH 2/2] updating ctime and mtime at syncing

[Anton Salikhmetov]

2008/1/15, Miklos Szeredi <miklos@szeredi.hu>:
> > Thanks for your review, Peter and Miklos!
> >
> > I overlooked this case when AS_MCTIME flag has been turned off and the
> > page is still dirty.
> >
> > On the other hand, the words "shall be marked for update" may be
> > considered as just setting the AS_MCTIME flag, not updating the time
> > stamps.
> >
> > What do you think about calling mapping_update_time() inside of "if
> > (MS_SYNC & flags)"? I suggest such change because the code for
> > analysis of the case you've mentioned above seems impossible to me.
>
> I think that's a good idea.  As a first iteration, just updating the
> mtime/ctime in msync(MS_SYNC) and remove_vma() (called at munmap time)
> would be a big improvement over what we currently have.
>
> I would also recommend, that you drop mapping_update_time() and the
> related functions from the patch, and just use file_update_time()
> instead.

Thank you for your recommendations. I will submit my new solution shortly.

By the way, I've already changed the unlink_file_vma() function.

>
> Miklos
>

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Re: [PATCH 2/2] updating ctime and mtime at syncing

[Anton Salikhmetov]

2008/1/14, Miklos Szeredi <miklos@szeredi.hu>:
> > 2008/1/14, Miklos Szeredi <miklos@szeredi.hu>:
> > > > http://bugzilla.kernel.org/show_bug.cgi?id=2645
> > > >
> > > > Changes for updating the ctime and mtime fields for memory-mapped files:
> > > >
> > > > 1) new flag triggering update of the inode data;
> > > > 2) new function to update ctime and mtime for block device files;
> > > > 3) new helper function to update ctime and mtime when needed;
> > > > 4) updating time stamps for mapped files in sys_msync() and do_fsync();
> > > > 5) implementing the feature of auto-updating ctime and mtime.
> > >
> > > How exactly is this done?
> > >
> > > Is this catering for this case:
> > >
> > >  1 page is dirtied through mapping
> > >  2 app calls msync(MS_ASYNC)
> > >  3 page is written again through mapping
> > >  4 app calls msync(MS_ASYNC)
> > >  5 ...
> > >  6 page is written back
> > >
> > > What happens at 4?  Do we care about this one at all?
> >
> > The POSIX standard requires updating the file times every time when msync()
> > is called with MS_ASYNC. I.e. the time stamps should be updated even
> > when no physical synchronization is being done immediately.
>
> Yes.  However, on linux MS_ASYNC is basically a no-op, and without
> doing _something_ with the dirty pages (which afaics your patch
> doesn't do), it's impossible to observe later writes to the same page.
>
> I don't advocate full POSIX conformance anymore, because it's probably
> too expensive to do (I've tried).  Rather than that, we should
> probably find some sane compromise, that just fixes the real life
> issue.  Here's a pointer to the thread about this:
>
> http://lkml.org/lkml/2007/3/27/55
>
> Your patch may be a good soultion, but you should describe in detail
> what it does when pages are dirtied, and when msync/fsync are called,
> and what happens with multiple msync calls that I've asked about.
>
> I suspect your patch is ignoring writes after the first msync, but
> then why care about msync at all?  What's so special about the _first_
> msync?  Is it just that most test programs only check this, and not
> what happens if msync is called more than once?  That would be a bug
> in the test cases.
>
> > > > +/*
> > > > + * Update the ctime and mtime stamps for memory-mapped block device files.
> > > > + */
> > > > +static void bd_inode_update_time(struct inode *inode)
> > > > +{
> > > > +     struct block_device *bdev = inode->i_bdev;
> > > > +     struct list_head *p;
> > > > +
> > > > +     if (bdev == NULL)
> > > > +             return;
> > > > +
> > > > +     mutex_lock(&bdev->bd_mutex);
> > > > +     list_for_each(p, &bdev->bd_inodes) {
> > > > +             inode = list_entry(p, struct inode, i_devices);
> > > > +             inode_update_time(inode);
> > > > +     }
> > > > +     mutex_unlock(&bdev->bd_mutex);
> > > > +}
> > >
> > > Umm, why not just call with file->f_dentry->d_inode, so that you don't
> > > need to do this ugly search for the physical inode?  The file pointer
> > > is available in both msync and fsync.
> >
> > I'm not sure if I undestood your question. I see two possible
> > interpretations for this question, and I'm answering both.
> >
> > The intention was to make the data changes in the block device data
> > visible to all device files associated with the block device. Hence
> > the search, because the time stamps for all such device files should
> > be updated as well.
>
> Ahh, but it will only update "active" devices, which are currently
> open, no?  Is that what we want?
>
> > Not only the sys_msync() and do_fsync() routines call the helper
> > function mapping_update_time().
>
> Ah yes, __sync_single_inode() calls it as well.  Why?

The __sync_single_inode() function calls mapping_update_time()
to enable the "auto-updating" feature discussed earlier.

>
> Miklos
>

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