Subject: [PATCH] block_dev.c: fsync() on close() considered harmful
From: Miquel van Smoorenburg <[email-masked]>
To: Andrea Arcangeli <[email-masked]>
Cc: [email-masked]
Date: Thu, 22 Nov 2001 14:34:50 +0100

I'm running an INN usenet news server that uses raw partitions for
storage. I.e. it opens /dev/sda7 etc. and mmap()s [which finally
works in 2.4, hurray]

Even though the server is keeping those devices open, when a utility
program (sm) opens that file/device and closes() it the close() causes
a fsync() on the device, something that is not wanted.

I applied the following patch which fixes it for me, it prevents
the sync-after-close if it was close() calling blkdev_put()
and we're not the last one to call blkdev_put().

That means fsync() will still be done on unmounts or when the
last user of the device closes it, but not otherwise.

Is this correct or am I overlooking something?

--- linux-2.4.15-pre8/fs/block_dev.c.orig	Thu Oct 25 22:58:35 2001
+++ linux-2.4.15-pre8/fs/block_dev.c	Wed Nov 21 13:32:16 2001
@@ -603,7 +603,7 @@
 
	down(&bdev->bd_sem);
	lock_kernel();
-	if (kind == BDEV_FILE)
+	if (kind == BDEV_FILE && bdev->bd_openers == 1)
		__block_fsync(bd_inode);
	else if (kind == BDEV_FS)
		fsync_no_super(rdev);

Mike.
-- 
"Only two things are infinite, the universe and human stupidity,
 and I'm not sure about the former" -- Albert Einstein.