[PATCH] [nfs-utils] fix issue: mount -osharecache failure but return 'true'

[jiyin@redhat.com]

From: "Jianhong.Yin" <yin-jianhong@163.com>

see: https://bugzilla.redhat.com/show_bug.cgi?id=1629705
mount.nfs4 -o context=system_u:object_r:user_home_dir_t:s0,sharecache $serv:$expdir $nfsmp
mount.nfs4 -o context=system_u:object_r:xferlog_t:s0,sharecache $serv:$expdir $nfsmp2
^^^ here mount fail, but return true. it confuse user!

according: https://patchwork.kernel.org/patch/10602607/#22234047
add function is_mounted_already()
-		if (errno == EBUSY)
+		if (errno == EBUSY && is_mounted_already(mi->spec, mi->node))
			return EX_SUCCESS;

Signed-off-by: Jianhong Yin <yin-jianhong@163.com>
---
 utils/mount/stropts.c | 31 ++++++++++++++++++++++++-------
 1 file changed, 24 insertions(+), 7 deletions(-)

diff --git a/utils/mount/stropts.c b/utils/mount/stropts.c
index 4d2e37e..4be7e61 100644
--- a/utils/mount/stropts.c
+++ b/utils/mount/stropts.c
@@ -48,6 +48,7 @@
 #include "version.h"
 #include "parse_dev.h"
 #include "conffile.h"
+#include <mntent.h>
 
 #ifndef NFS_PROGRAM
 #define NFS_PROGRAM	(100003)
@@ -1056,6 +1057,27 @@ static int nfs_is_permanent_error(int error)
 	}
 }
 
+static int is_mounted_already(const char *fsname, const char *dir)
+{
+	struct mntent *ent;
+	FILE *fp;
+	int ret = 0;
+
+	fp = setmntent("/proc/mounts", "r");
+	if (fp == NULL) {
+		perror("[unlikely] setmntent(3) fail");
+		exit(1);
+	}
+	while (NULL != (ent = getmntent(fp))) {
+		if (!strcmp(ent->mnt_fsname, fsname) && !strcmp(ent->mnt_dir, dir)) {
+			ret = 1;
+			break;
+		}
+	}
+	endmntent(fp);
+	return ret;
+}
+
 /*
  * Handle "foreground" NFS mounts.
  *
@@ -1078,13 +1100,8 @@ static int nfsmount_fg(struct nfsmount_info *mi)
 		if (nfs_try_mount(mi))
 			return EX_SUCCESS;
 
-		if (errno == EBUSY)
-			/* The only cause of EBUSY is if exactly the desired
-			 * filesystem is already mounted.  That can arguably
-			 * be seen as success.  "mount -a" tries to optimise
-			 * out this case but sometimes fails.  Help it out
-			 * by pretending everything is rosy
-			 */
+		/* if EBUSY is caused by re-mount, ignore the error */
+		if (errno == EBUSY && is_mounted_already(mi->spec, mi->node))
 			return EX_SUCCESS;
 
 		if (nfs_is_permanent_error(errno))
-- 
2.17.1