mountd: fix checking for errors when exporting filesystems

commit 5604b35a61e22930873ffc4e9971002f578e7978
  nfs-utils: Increase the stdio file buffer size for procfs files

changed writes to some sysfs files to be line buffered (_IOLBF) where
they weren't before.  While this probably makes sense, it introduced a
bug.

With fully buffered streams, you don't expect to get an error until you
call fflush(). With line buffered streams you can get the error
from fprintf() et al.

qword_eol() only tests the return from fflush(), not from fprintf().
Consequently errors were not noticed.

One result of this is that if you export, with crossmnt, a filesystem
underneath which are mounted non-exportable filesystems (e.g. /proc)
then an 'ls -l' on the client will block indefinitely waiting for a
meaningful 'yes' or 'no' from the server, but will never get one.

This patch changes qword_eol to test both fprintf and fflush.

Acked-by: J. Bruce Fields <bfields@fieldses.org>
Signed-off-by: NeilBrown <neilb@suse.de>
Signed-off-by: Steve Dickson <steved@redhat.com>

diff --git a/support/nfs/cacheio.c b/support/nfs/cacheio.c
index e641c4535c652c803dc067e4cfe3f4633bc28b12..61e07a8257c961a7815ac0ae3816352cf14cfba5 100644 (file)
--- a/support/nfs/cacheio.c
+++ b/support/nfs/cacheio.c
@@ -162,11 +162,16 @@ int qword_eol(FILE *f)
 {
        int err;
 
-       fprintf(f,"\n");
-       err = fflush(f);
-       if (err) {
-               xlog_warn("qword_eol: fflush failed: errno %d (%s)",
+       err = fprintf(f,"\n");
+       if (err < 0) {
+               xlog_warn("qword_eol: fprintf failed: errno %d (%s)",
                            errno, strerror(errno));
+       } else {
+               err = fflush(f);
+               if (err) {
+                       xlog_warn("qword_eol: fflush failed: errno %d (%s)",
+                                 errno, strerror(errno));
+               }
        }
        /*
         * We must send one line (and one line only) in a single write