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

[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?

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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