On Thu, May 9, 2019 at 4:43 AM Dave Chinner <david@xxxxxxxxxxxxx> wrote: > > On Thu, May 02, 2019 at 10:30:43PM -0400, Theodore Ts'o wrote: > > On Thu, May 02, 2019 at 01:39:47PM -0400, Amir Goldstein wrote: > > > I am not saying there is no room for a document that elaborates on those > > > guaranties. I personally think that could be useful and certainly think that > > > your group's work for adding xfstest coverage for API guaranties is useful. > > > > Again, here is my concern. If we promise that ext4 will always obey > > Dave Chinner's SOMC model, it would forever rule out Daejun Park and > > Dongkun Shin's "iJournaling: Fine-grained journaling for improving the > > latency of fsync system call"[1] published in Usenix ATC 2017. > > No, it doesn't rule that out at all. > Dave and all the good people, Please go back to read the first email in this thread before it diverged yet again into interpretations of SOMC. The novelty in my proposal (which I attribute to Jan's idea) is to reduce the concerns around documenting "expected behavior of the world" to documenting "expected behavior of linking an O_TMPFILE". It boils down to documenting AT_LINK_ATOMIC (or whatever flag name): ""The filesystem provided the guaranty that after a crash, if the linked O_TMPFILE is observed in the target directory, than all the data and metadata modifications made to the file before being linked are also observed." No more, no less. I intentionally reduced the scope to the point that I could get ext4,btrfs to sign the treaty. I think this is a good starting point, from which we can make forward progress. I'd appreciate if xfs camp, Dave in particular, would address the proposal regardless of the broader SOMC documentation discussion. Thanks, Amir.
