Jörn Engel wrote: > 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(). You're right. Though, doesn't normal page writeback enqueue the COW metadata changes? If not, how do they get written in a timely fashion? -- Jamie - To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
