On Wednesday, 8 November 2006 00:49, Alasdair G Kergon wrote:
> On Wed, Nov 08, 2006 at 12:05:49AM +0100, Rafael J. Wysocki wrote:
> > But freeze_bdev() is supposed to return the result of get_super(bdev)
> > _unconditionally_. Moreover, in its current form freeze_bdev() _cannot_
> > _fail_, so I don't see how this change doesn't break any existing code.
> > For example freeze_filesystems() (recently added to -mm) will be broken
> > if the down_trylock() is unsuccessful.
>
> I hadn't noticed that -mm patch. I'll take a look. Up to now, device-mapper
> (via dmsetup) and xfs (via xfs_freeze, which dates from before device-mapper
> handled this automatically) were the only users. Only one freeze should be
> issued at once. A freeze is a temporary thing, normally used while creating a
> snapshot. (One problem we still have is lots of old documentation on the web
> advising people to run xfs_freeze before creating device-mapper snapshots.)
>
> You're right that the down_trylock idea is more trouble than it's worth and
> should be scrapped.
Well, having looked at it once again I think I was wrong that this change would
break freeze_filesystems(), because it only calls freeze_bdev() after checking
if sb->s_frozen is not set to SB_FREEZE_TRANS (freeze_filesystems() is only
called after all of the userspace processes have been frozen).
However, XFS_IOC_FREEZE happily returns 0 after calling freeze_bdev(),
apparetnly assuming that it won't fail.
Greetings,
Rafael
--
You never change things by fighting the existing reality.
R. Buckminster Fuller
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