[nfs-utils PATCH] mountd: fix checking for errors when exporting filesystems.

[NeilBrown <neilb@suse.de>]

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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.

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

diff --git a/support/nfs/cacheio.c b/support/nfs/cacheio.c
index e641c45..61e07a8 100644
--- 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

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