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[dm-devel] Re: [RFC PATCH 1/3] Implement generic freeze feature



Hi,

On Mon, Apr 28, 2008 at 07:31:23PM +0900, Takashi Sato wrote:
+ /* Initialize semaphore for freeze. */
+ sema_init(&bdev->bd_freeze_sem, 1);

The freezing process is already protected by bd_mount_sem, so I don't
think there's need for another one.

[...]
 down(&bdev->bd_mount_sem);
 sb = get_super(bdev);

I think the protection against double freezes would be better done by
using a trylock on bd_mount_sem.

bd_mount_sem can protect against only freezes and cannot protect against
unfreezes.  If multiple unfreezes run in parallel,  the multiple up() for
bd_mount_sem might occur incorrectly.

In fact after that it could be changed
from a semaphore to a simple test_and_set_bit.

I will consider using test_and_set_bit.

 error = -ENOTTY;
 break;
+
+ case FIFREEZE: {

This would be better to split intot a small helper ala ioctl_fibmap()

+ case FITHAW: {

Same here.

OK.  I will split small helper functions.

Cheers, Takashi
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