[PATCH 2/2][RFC][BUG] msync: updating ctime and mtime at syncing

[Anton Salikhmetov <salikhmetov@gmail.com>]

The patch contains changes for updating the ctime and mtime fields for memory mapped files:

1) adding a new flag triggering update of the inode data;
2) implementing a helper function for checking that flag and updating ctime and mtime;
3) updating time stamps for mapped files in sys_msync() and do_fsync().

Signed-off-by: Anton Salikhmetov <salikhmetov@gmail.com>

---

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/inode.c b/fs/inode.c
index ed35383..c5b954e 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -22,6 +22,7 @@
 #include <linux/bootmem.h>
 #include <linux/inotify.h>
 #include <linux/mount.h>
+#include <linux/file.h>
 
 /*
  * This is needed for the following functions:
@@ -1282,6 +1283,18 @@ void file_update_time(struct file *file)
 
 EXPORT_SYMBOL(file_update_time);
 
+/*
+ * Update the ctime and mtime stamps after checking if they are to be updated.
+ */
+void mapped_file_update_time(struct file *file)
+{
+	if (test_and_clear_bit(AS_MCTIME, &file->f_mapping->flags)) {
+		get_file(file);
+		file_update_time(file);
+		fput(file);
+	}
+}
+
 int inode_needs_sync(struct inode *inode)
 {
 	if (IS_SYNC(inode))
diff --git a/fs/sync.c b/fs/sync.c
index 7cd005e..df57507 100644
--- a/fs/sync.c
+++ b/fs/sync.c
@@ -87,6 +87,8 @@ long do_fsync(struct file *file, int datasync)
 		goto out;
 	}
 
+	mapped_file_update_time(file);
+
 	ret = filemap_fdatawrite(mapping);
 
 	/*
diff --git a/include/linux/fs.h b/include/linux/fs.h
index b3ec4a4..0b05118 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1978,6 +1978,7 @@ 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 mapped_file_update_time(struct file *file);
 
 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 e788f7b..9d0a8f9 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
@@ -74,14 +79,17 @@ 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)) {
+			mapped_file_update_time(file);
+			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;
 	}

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