Messages in this thread | | | Date | Tue, 26 Feb 2008 18:02:14 +0100 | From | Jörn Engel <> | Subject | Re: Proposal for "proper" durable fsync() and fdatasync() |
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On Tue, 26 February 2008 15:28:10 +0000, Jamie Lokier wrote: > > > One interesting aspect of this comes with COW filesystems like btrfs or > > logfs. Writing out data pages is not sufficient, because those will get > > lost unless their referencing metadata is written as well. So either we > > have to call fsync for those filesystems or add another callback and let > > filesystems override the default implementation. > > Doesn't the ->fsync callback get called in the sys_fdatasync() case, > with appropriate arguments?
My paragraph above was aimed at the sync_file_range() case. fsync and fdatasync do the right thing within the limitations you brought up in this thread. sync_file_range() without further changes will only write data pages, not the metadata required to actually access those data pages. This works just fine for non-COW filesystems, which covers all currently merged ones.
With COW filesystems it is currently impossible to do sync_file_range() properly. The problem is orthogonal to your's, I just brought it up since you were already mentioning sync_file_range().
Jörn
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