Return-Path: Received: from mail-wm0-f67.google.com ([74.125.82.67]:36022 "EHLO mail-wm0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751689AbdI1QTL (ORCPT ); Thu, 28 Sep 2017 12:19:11 -0400 Cc: mtk.manpages@gmail.com, linux-man@vger.kernel.org, "linux-nfs@vger.kernel.org" , "linux-fsdevel@vger.kernel.org" Subject: Re: [RFC PATCH manpages] write.2, fsync.2, close.2: update description of error codes To: NeilBrown , Jeff Layton , Trond Myklebust , "anna.schumaker@netapp.com" , "jlayton@kernel.org" References: <20170720194227.7830-1-jlayton@kernel.org> <1503683981.22608.0.camel@redhat.com> <87h8wsiog4.fsf@notabene.neil.brown.name> <1503920855.4563.12.camel@redhat.com> <87pobfgo9q.fsf@notabene.neil.brown.name> <1504004058.4679.7.camel@redhat.com> <87efrjb2mn.fsf@notabene.neil.brown.name> <1504784132.4954.12.camel@redhat.com> <1504796087.3561.7.camel@primarydata.com> <874ls9diij.fsf@notabene.neil.brown.name> <1505126785.4916.7.camel@redhat.com> <87poawc390.fsf@notabene.neil.brown.name> <1505229616.28831.26.camel@redhat.com> <87efrbbne1.fsf@notabene.neil.brown.name> <1505305391.4822.13.camel@redhat.com> <87ingm9n04.fsf@notabene.neil.brown.name> <1505386139.4870.10.camel@redhat.com> <87fub75xxr.fsf@notabene.neil.brown.name> From: "Michael Kerrisk (man-opages)" Message-ID: <97a7dd08-d736-cf83-052e-af4fb6596a02@gmail.com> Date: Thu, 28 Sep 2017 18:19:06 +0200 MIME-Version: 1.0 In-Reply-To: <87fub75xxr.fsf@notabene.neil.brown.name> Content-Type: text/plain; charset=utf-8; format=flowed Sender: linux-nfs-owner@vger.kernel.org List-ID: Hi Neil, On 09/28/2017 05:01 AM, NeilBrown wrote: > On Thu, Sep 14 2017, Jeff Layton wrote: > >>> .TP >>> .B EIO >>> -An error occurred during synchronization. >>> +An error occurred during synchronization. This error may relate >>> +to data written to some other file descriptor on the same file. >>> +.\" commit 088737f44bbf6378745f5b57b035e57ee3dc4750 >>> +Since Linux 4.13 errors from write-back will be reported to >>> +all file descriptors that might have written the data which triggered >>> +the error, and which are still open. >> >> This is a little awkward. How could we report to a fd that was no longer >> open? How about: >> >> "Since Linux 4.13, errors from write-back will be reported to all file >> descriptors that were open at the time that the error was recorded." > > That might be simpler, but it is less correct. As I go on to say, NFS > *doesn't* report on all file descriptors that were open at that time. > > I've changed it to > > ------------------- > Since Linux 4.13, errors from write-back will be reported to > all file descriptors that might have written the data which triggered > the error. Some filesystems (e.g. NFS) keep close track of which data > came through which file descriptor, and give precise reporting. > Other filesystems (e.g. most local filesystems) will report errors to > all file descriptors that where open on the file when the error was recorded. > ------------------ > > which includes some of your text, and removes the "that are still open" > which probably doesn't help. > >>> .TP >>> .B EIO >>> A low-level I/O error occurred while modifying the inode. >>> +This error may relate to data written by an earlier >>> +.BR write (2), >>> +which may have been issued to a different file descriptor on >>> +the same file. Since Linux 4.13 errors from write-back will >>> +be reported to all file descriptors that might have >>> +written the data which triggered the error, and which are still >>> +open. >> >> >> This is where things get a little more vague. >> >> Some filesystems will return errors on a subsequent write(2) when >> previous writeback has failed -- some don't. In either case though, >> write(2) should never advance your errseq_t cursor, so only an fsync >> will "clear" an earlier error. >> >> I'm not sure how best to convey that in the manpages though. > > How about: > > ------------- > This error may relate to the write-back of data written by an > earlier > .BR write (2), > which may have been issued to a different file descriptor on > the same file. Since Linux 4.13, errors from write-back come > with a promise that they > .I may > be reported by subsequent. > .BR write (2) > requests, and > .I will > be reported by a subsequent > .BR fsync (2) > (whether or not they were also reported by > .BR write (2)). > ------------ > ?? > > Those changes are included in the following. > > Thanks, > NeilBrown > > From: NeilBrown > Date: Thu, 14 Sep 2017 09:44:43 +1000 > Subject: [PATCH] write.2, fsync.2, close.2: update description of error codes > > Since 4.13, errors from writeback are more reliably reported > to all file descriptors that might be relevant. > > Add notes to this effect, and also add detail about ENOSPC and EDQUOT > which can be delayed in a similar many to EIO - for NFS in particular. > > Signed-off-by: NeilBrown Thanks! I've applied, and added Jeff's Reviewed-by. Cheers, Michael > --- > man2/close.2 | 9 +++++++++ > man2/fsync.2 | 18 +++++++++++++++++- > man2/write.2 | 28 +++++++++++++++++++++++++--- > 3 files changed, 51 insertions(+), 4 deletions(-) > > diff --git a/man2/close.2 b/man2/close.2 > index 55d89ed3dbc7..136bd0be3f67 100644 > --- a/man2/close.2 > +++ b/man2/close.2 > @@ -82,6 +82,15 @@ call was interrupted by a signal; see > .TP > .B EIO > An I/O error occurred. > +.TP > +.BR ENOSPC ", " EDQUOT > +On NFS, these errors are not normally reported against the first write > +which exceeds the available storage space, but instead against a > +subsequent > +.BR write (2), > +.BR fsync (2), > +or > +.BR close (2). > .PP > See NOTES for a discussion of why > .BR close () > diff --git a/man2/fsync.2 b/man2/fsync.2 > index eed3c460bea9..c7878bf3496f 100644 > --- a/man2/fsync.2 > +++ b/man2/fsync.2 > @@ -121,7 +121,15 @@ is set appropriately. > is not a valid open file descriptor. > .TP > .B EIO > -An error occurred during synchronization. > +An error occurred during synchronization. This error may relate > +to data written to some other file descriptor on the same file. > +.\" commit 088737f44bbf6378745f5b57b035e57ee3dc4750 > +Since Linux 4.13, errors from write-back will be reported to > +all file descriptors that might have written the data which triggered > +the error. Some filesystems (e.g. NFS) keep close track of which data > +came through which file descriptor, and give more precise reporting. > +Other filesystems (e.g. most local filesystems) will report errors to > +all file descriptors that where open on the file when the error was recorded. > .TP > .B ENOSPC > Disk space was exhausted while synchronizing. > @@ -130,6 +138,14 @@ Disk space was exhausted while synchronizing. > .I fd > is bound to a special file (e.g., a pipe, FIFO, or socket) > which does not support synchronization. > +.TP > +.BR ENOSPC ", " EDQUOT > +.I fd > +is bound to a file on NFS or another filesystem which does not allocate > +space at the time of a > +.BR write (2) > +system call, and some previous write failed due to insufficient > +storage space. > .SH CONFORMING TO > POSIX.1-2001, POSIX.1-2008, 4.3BSD. > .SH AVAILABILITY > diff --git a/man2/write.2 b/man2/write.2 > index 061aa70cf590..b1cc3a2cfb17 100644 > --- a/man2/write.2 > +++ b/man2/write.2 > @@ -47,7 +47,7 @@ write \- write to a file descriptor > .BR write () > writes up to > .I count > -bytes from the buffer pointed > +bytes from the buffer starting at > .I buf > to the file referred to by the file descriptor > .IR fd . > @@ -181,6 +181,22 @@ or the file offset is not suitably aligned. > .TP > .B EIO > A low-level I/O error occurred while modifying the inode. > +This error may relate to the write-back of data written by an > +earlier > +.BR write (2), > +which may have been issued to a different file descriptor on > +the same file. Since Linux 4.13, errors from write-back come > +with a promise that they > +.I may > +be reported by subsequent. > +.BR write (2) > +requests, and > +.I will > +be reported by a subsequent > +.BR fsync (2) > +(whether or not they were also reported by > +.BR write (2)). > +.\" commit 088737f44bbf6378745f5b57b035e57ee3dc4750 > .TP > .B ENOSPC > The device containing the file referred to by > @@ -222,8 +238,14 @@ unsigned and signed integer data types specified by POSIX.1. > A successful return from > .BR write () > does not make any guarantee that data has been committed to disk. > -In fact, on some buggy implementations, it does not even guarantee > -that space has successfully been reserved for the data. > +On some filesystems, including NFS, it does not even guarantee > +that space has successfully been reserved for the data. In the case, > +some errors might be delayed to a future > +.BR write (2) > +or to > +.BR fsync (2) > +or even > +.BR close (2). > The only way to be sure is to call > .BR fsync (2) > after you are done writing all your data. >