On Tue, 2017-04-04 at 09:12 -0700, Matthew Wilcox wrote: > On Tue, Apr 04, 2017 at 08:17:48AM -0400, Jeff Layton wrote: > > Agreed that we should focus on POSIX compliance. I'll also note that > > POSIX states: > > > > "If more than one error occurs in processing a function call, any one > > of the possible errors may be returned, as the order of > > detection is undefined." > > > > http://pubs.opengroup.org/onlinepubs/9699919799/functions/V2_chap02.html#tag_15_03 > > > > So, I'd like to push back on this idea that we need to prefer reporting > > -EIO over other errors. POSIX certainly doesn't mandate that. > > I honestly wonder if we need to support ENOSPC from writeback at all. > Looking at our history, the AS_EIO / AS_ENOSPC came from this patch > in 2003: > > https://git.kernel.org/pub/scm/linux/kernel/git/tglx/history.git/commit/?id=fcad2b42fc2e15a94ba1a1ba8535681a735bfd16 > > That seems to come from here: > http://lkml.iu.edu/hypermail/linux/kernel/0308.0/0205.html > which is marked as a resend, but I can't find the original. > > It's a little misleading because the immediately preceding patch > introduced mapping->error, so there's no precedent here to speak of. > It looks like we used to just silently lose writeback errors (*cough*). > > I'd like to suggest that maybe we don't need to support multiple errors > at all. That all errors, including ENOSPC, get collapsed into EIO. > POSIX already tells us to do that for close() and permits us to do that > for fsync(). > That is certainly allowed under POSIX as I interpret the spec. At a minimum we just need a single flag and can collapse all errors under that. That said, I think giving more specific errors where we can is useful. When your program is erroring out and writing 'I/O error' to the logs, then how much time will your admins burn before they figure out that it really failed because the filesystem was full? -- Jeff Layton <jlayton@xxxxxxxxxx>
