Change /etc/mtab to /proc/self/mounts

Fix misleading error message:

 "The /dev/zfs device is missing and must be created.", if /etc/mtab is missing.

Reviewed-by: Richard Laager <rlaager@wiktel.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Eric Desrochers <eric.desrochers@canonical.com>
Closes #4680 
Closes #5029

cmd/mount_zfs/mount_zfs.c

@@ -294,11 +294,11 @@ mtab_is_writeable(void)
 	struct stat st;
 	int error, fd;
 
-	error = lstat(MNTTAB, &st);
+	error = lstat("/etc/mtab", &st);
 	if (error || S_ISLNK(st.st_mode))
 		return (0);
 
-	fd = open(MNTTAB, O_RDWR | O_CREAT, 0644);
+	fd = open("/etc/mtab", O_RDWR | O_CREAT, 0644);
 	if (fd < 0)
 		return (0);
 
@@ -320,21 +320,21 @@ mtab_update(char *dataset, char *mntpoint, char *type, char *mntopts)
 	mnt.mnt_freq = 0;
 	mnt.mnt_passno = 0;
 
-	fp = setmntent(MNTTAB, "a+");
+	fp = setmntent("/etc/mtab", "a+");
 	if (!fp) {
 		(void) fprintf(stderr, gettext(
-		    "filesystem '%s' was mounted, but %s "
+		    "filesystem '%s' was mounted, but /etc/mtab "
 		    "could not be opened due to error %d\n"),
-		    dataset, MNTTAB, errno);
+		    dataset, errno);
 		return (MOUNT_FILEIO);
 	}
 
 	error = addmntent(fp, &mnt);
 	if (error) {
 		(void) fprintf(stderr, gettext(
-		    "filesystem '%s' was mounted, but %s "
+		    "filesystem '%s' was mounted, but /etc/mtab "
 		    "could not be updated due to error %d\n"),
-		    dataset, MNTTAB, errno);
+		    dataset, errno);
 		return (MOUNT_FILEIO);
 	}
 

cmd/zfs/zfs_main.c

@@ -6146,9 +6146,10 @@ share_mount(int op, int argc, char **argv)
 		}
 
 		/*
-		 * When mount is given no arguments, go through /etc/mtab and
-		 * display any active ZFS mounts.  We hide any snapshots, since
-		 * they are controlled automatically.
+		 * When mount is given no arguments, go through
+		 * /proc/self/mounts and display any active ZFS mounts.
+		 * We hide any snapshots, since they are controlled
+		 * automatically.
 		 */
 
 		/* Reopen MNTTAB to prevent reading stale data from open file */
@@ -6228,8 +6229,8 @@ unshare_unmount_compare(const void *larg, const void *rarg, void *unused)
 
 /*
  * Convenience routine used by zfs_do_umount() and manual_unmount().  Given an
- * absolute path, find the entry /etc/mtab, verify that its a ZFS filesystem,
- * and unmount it appropriately.
+ * absolute path, find the entry /proc/self/mounts, verify that its a
+ * ZFS filesystems, and unmount it appropriately.
  */
 static int
 unshare_unmount_path(int op, char *path, int flags, boolean_t is_manual)
@@ -6242,7 +6243,7 @@ unshare_unmount_path(int op, char *path, int flags, boolean_t is_manual)
 	ino_t path_inode;
 
 	/*
-	 * Search for the path in /etc/mtab.  Rather than looking for the
+	 * Search for the path in /proc/self/mounts. Rather than looking for the
 	 * specific path, which can be fooled by non-standard paths (i.e. ".."
 	 * or "//"), we stat() the path and search for the corresponding
 	 * (major,minor) device pair.
@@ -6273,8 +6274,8 @@ unshare_unmount_path(int op, char *path, int flags, boolean_t is_manual)
 			    "currently mounted\n"), cmdname, path);
 			return (1);
 		}
-		(void) fprintf(stderr, gettext("warning: %s not in mtab\n"),
-		    path);
+		(void) fprintf(stderr, gettext("warning: %s not in"
+		    "/proc/self/mounts\n"), path);
 		if ((ret = umount2(path, flags)) != 0)
 			(void) fprintf(stderr, gettext("%s: %s\n"), path,
 			    strerror(errno));
@@ -6385,9 +6386,9 @@ unshare_unmount(int op, int argc, char **argv)
 		/*
 		 * We could make use of zfs_for_each() to walk all datasets in
 		 * the system, but this would be very inefficient, especially
-		 * since we would have to linearly search /etc/mtab for each
-		 * one.  Instead, do one pass through /etc/mtab looking for
-		 * zfs entries and call zfs_unmount() for each one.
+		 * since we would have to linearly search /proc/self/mounts for
+		 * each one. Instead, do one pass through /proc/self/mounts
+		 * looking for zfs entries and call zfs_unmount() for each one.
 		 *
 		 * Things get a little tricky if the administrator has created
 		 * mountpoints beneath other ZFS filesystems.  In this case, we

cmd/zinject/translate.c

@@ -120,7 +120,7 @@ parse_pathname(const char *inpath, char *dataset, char *relpath,
 #else
 	if ((fp = fopen(MNTTAB, "r")) == NULL) {
 #endif
-		(void) fprintf(stderr, "cannot open /etc/mtab\n");
+		(void) fprintf(stderr, "cannot open %s\n", MNTTAB);
 		return (-1);
 	}