Print mount/umount errors

Because we are dependent of the system mount/umount utilities to
ensure correct mtab locking, we should not suppress their error
output.  During a successful mount/umount they will be silent,
but during a failure the error message they print is the only sure
way to know why a mount failed.  This is because the (u)mount(8)
return code does not contain the result of the system call issued.
The only way to clearly idenify why thing failed is to rely on
the error message printed by the tool.

Longer term once libmount is available we can issue the mount/umount
system calls within the tool and still be ensured correct mtab locking.

Closed #107

3 files changed, 18 insertions, 9 deletions

diff --git a/include/libzfs.h b/include/libzfs.h
index 082b690e9..e0c695043 100644
--- a/include/libzfs.h
+++ b/include/libzfs.h
@@ -675,7 +675,10 @@ extern int zfs_nicestrtonum(libzfs_handle_t *, const char *, uint64_t *);
 /*
  * Utility functions to run an external process.
  */
-int libzfs_run_process(const char *, char **);
+#define	STDOUT_VERBOSE	0x01
+#define	STDERR_VERBOSE	0x02
+
+int libzfs_run_process(const char *, char **, int flags);
 int libzfs_load_module(const char *);
 
 /*
diff --git a/lib/libzfs/libzfs_mount.c b/lib/libzfs/libzfs_mount.c
index a1faf49d1..1dc58f924 100644
--- a/lib/libzfs/libzfs_mount.c
+++ b/lib/libzfs/libzfs_mount.c
@@ -269,7 +269,7 @@ do_mount(const char *src, const char *mntpt, char *opts)
 	int rc;
 
 	/* Return only the most critical mount error */
-	rc = libzfs_run_process(argv[0], argv);
+	rc = libzfs_run_process(argv[0], argv, STDOUT_VERBOSE|STDERR_VERBOSE);
 	if (rc) {
 		if (rc & MOUNT_FILEIO)
 			return EIO;
@@ -310,7 +310,7 @@ do_unmount(const char *mntpt, int flags)
 	}
 
 	argv[count] = (char *)mntpt;
-	rc = libzfs_run_process(argv[0], argv);
+	rc = libzfs_run_process(argv[0], argv, STDOUT_VERBOSE|STDERR_VERBOSE);
 
 	return (rc ? EINVAL : 0);
 }
@@ -414,8 +414,10 @@ zfs_mount(zfs_handle_t *zhp, const char *options, int flags)
 static int
 unmount_one(libzfs_handle_t *hdl, const char *mountpoint, int flags)
 {
-	if (do_unmount(mountpoint, flags) != 0) {
-		zfs_error_aux(hdl, strerror(errno));
+	int error;
+
+	error = do_unmount(mountpoint, flags);
+	if (error != 0) {
 		return (zfs_error_fmt(hdl, EZFS_UMOUNTFAILED,
 		    dgettext(TEXT_DOMAIN, "cannot unmount '%s'"),
 		    mountpoint));
diff --git a/lib/libzfs/libzfs_util.c b/lib/libzfs/libzfs_util.c
index 163cd1671..da1b9bcdd 100644
--- a/lib/libzfs/libzfs_util.c
+++ b/lib/libzfs/libzfs_util.c
@@ -632,15 +632,19 @@ libzfs_module_loaded(const char *module)
 }
 
 int
-libzfs_run_process(const char *path, char *argv[])
+libzfs_run_process(const char *path, char *argv[], int flags)
 {
 	pid_t pid;
 	int rc;
 
 	pid = vfork();
 	if (pid == 0) {
-		close(1);
-		close(2);
+		if (!(flags & STDOUT_VERBOSE))
+			close(STDOUT_FILENO);
+
+		if (!(flags & STDERR_VERBOSE))
+			close(STDERR_FILENO);
+
 		(void) execvp(path, argv);
 		_exit(-1);
 	} else if (pid > 0) {
@@ -665,7 +669,7 @@ libzfs_load_module(const char *module)
 	if (libzfs_module_loaded(module))
 		return 0;
 
-	return libzfs_run_process("/sbin/modprobe", argv);
+	return libzfs_run_process("/sbin/modprobe", argv, 0);
 }
 
 libzfs_handle_t *