sync.2: syncfs() now returns errors if writeback fails

A patch has been merged for v5.8 that changes how syncfs() reports
errors. Change the sync() manpage accordingly.

Signed-off-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>

man2/sync.2

@@ -86,11 +86,26 @@ to indicate the error.
 is always successful.
 .PP
 .BR syncfs ()
-can fail for at least the following reason:
+can fail for at least the following reasons:
 .TP
 .B EBADF
 .I fd
 is not a valid file descriptor.
+.TP
+.B EIO
+An error occurred during synchronization.
+This error may relate to data written to any file on the filesystem, or on
+metadata related to the filesytem itself.
+.TP
+.B ENOSPC
+Disk space was exhausted while synchronizing.
+.TP
+.BR ENOSPC ", " EDQUOT
+Data was written to a files 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 VERSIONS
 .BR syncfs ()
 first appeared in Linux 2.6.39;
@@ -121,6 +136,13 @@ or
 .BR syncfs ()
 provide the same guarantees as fsync called on every file in
 the system or filesystem respectively.
+.PP
+In mainline kernel versions prior to 5.8,
+.\" commit 735e4ae5ba28c886d249ad04d3c8cc097dad6336
+.BR syncfs ()
+will only fail when passed a bad file descriptor (EBADF). In 5.8
+and later kernels, it will also report an error if one or more inodes failed
+to be written back since the last syncfs call.
 .SH BUGS
 Before version 1.3.20 Linux did not wait for I/O to complete
 before returning.