[RFC PATCH manpages] write.2, fsync.2, close.2: update description of error codes

NeilBrown
2017-09-13T23:50:35Z

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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 details about ENOSPC and EDQUOT
which can be delayed in a similar manner to EIO - for NFS in particular.

Signed-off-by: NeilBrown <neilb@suse.com>
---

This is my summary of recent changes, and details that have been made
clear during the exploration of those changes.

I haven't mentioned the fact that EPERM can be returned by
write/fsync/close on NFS if the permissions on the server are changed.
We probably should ... are there other errors that are worth mentioning
along with EPERM, ENOSPC, EDQUOT ??

Thanks,
NeilBronw

man2/close.2 | 9 +++++++++
man2/fsync.2 | 19 ++++++++++++++++++-
man2/write.2 | 20 +++++++++++++++++---
3 files changed, 44 insertions(+), 4 deletions(-)

diff --git a/man2/close.2 b/man2/close.2
index 751ec322b1f1..9776c839b8b6 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 f1a01301da0f..e706a08d360d 100644
--- a/man2/fsync.2
+++ b/man2/fsync.2
@@ -120,12 +120,29 @@ 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, and which are still open. 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 on the same
+file.
.TP
.BR EROFS ", " EINVAL
.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 6a39b5b5541d..1a9a86b03b04 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 +181,14 @@ 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 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.
+.\" commit 088737f44bbf6378745f5b57b035e57ee3dc4750
.TP
.B ENOSPC
The device containing the file referred to by
@@ -222,8 +230,14 @@ 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.
--
2.14.0.rc0.dirty

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