Re: [PATCH] loop.c: respect bio barrier and sync

[Jens Axboe]

On Thu, May 04 2006, Constantine Sapuntzakis wrote:
> I believe that the loop block device does not currently respect
> barriers or syncs issued by its clients. As a result, I have seen
> corrupted log errors when a loopback mounted ext3 file system is
> remounted after a hard stop.
> 
> The attached patch attempts to fix this problem by respecting the
> barrier and sync flags on the I/O request. The sync_file function was
> cut-and-paste from the implementation of fsync (I think there's no fd
> so I can't call fsync) to allow the patch to be deployed as an updated
> module. Is there another function that could be used?
> 
> Comments are welcome. I am not on the list so please cc: me on any 
> response..

Please inline your patches, so one can actually comment on them...

- You should handle sync_file() failure. If we don't have !f_op (will
  that ever hit, btw?) or ->fsync(), then fail the barrier with
  -EOPNOTSUPP. For fsync failure, well... You probably want to just
  error the bio with -EIO then.

- bio_sync() doesn't have the semantics you define it to, it is a hint
  to the block layer to start request processing instead of plugging. So
  don't treat it as a barrier, ignore it.

- Does this work for all loop_device types?

-- 
Jens Axboe

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