Allow '-o remount' for non-legacy datasets

This is done for compatibility with existing Linux infrastructure.

In particular, when using zfs as a root filesystem there are init
scripts which as part of shutdown remount root read-only.  Also,
the new systemd infrastructure being used by Fedora expects to be
able to remount a file system read-write.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Issue #847

diff --git a/cmd/mount_zfs/mount_zfs.c b/cmd/mount_zfs/mount_zfs.c
index 45c291e04ce000ab3d56d84d6da58d4c8d7b1a28..0a69d69d79e3dedff28a5cfd3432dcbe3e436816 100644 (file)
--- a/cmd/mount_zfs/mount_zfs.c
+++ b/cmd/mount_zfs/mount_zfs.c
@@ -312,7 +312,7 @@ main(int argc, char **argv)
        char badopt[MNT_LINE_MAX] = { '\0' };
        char mtabopt[MNT_LINE_MAX] = { '\0' };
        char *dataset, *mntpoint;
-       unsigned long mntflags = 0, zfsflags = 0, remount_ro = 0;
+       unsigned long mntflags = 0, zfsflags = 0, remount = 0;
        int sloppy = 0, fake = 0, verbose = 0, nomtab = 0, zfsutil = 0;
        int error, c;
 
@@ -417,11 +417,10 @@ main(int argc, char **argv)
                    "  mountopts:  \"%s\"\n  mtabopts:   \"%s\"\n"),
                    dataset, mntpoint, mntflags, zfsflags, mntopts, mtabopt);
 
-       if (mntflags & MS_REMOUNT)
+       if (mntflags & MS_REMOUNT) {
                nomtab = 1;
-
-       if ((mntflags & MS_REMOUNT) && (mntflags & MS_RDONLY))
-               remount_ro = 1;
+               remount = 1;
+       }
 
        if (zfsflags & ZS_ZFSUTIL)
                zfsutil = 1;
@@ -454,9 +453,10 @@ main(int argc, char **argv)
         * we differentiate the two cases using the 'zfsutil' mount option.
         * This mount option should only be supplied by the 'zfs mount' util.
         *
-        * The only exception to the above rule is '-o remount,ro'.  This is
-        * always allowed for non-legacy datasets for rc.sysinit/umountroot
-        * to safely remount the root filesystem and flush its cache.
+        * The only exception to the above rule is '-o remount' which is
+        * always allowed for non-legacy datasets.  This is done because when
+        * using zfs as your root file system both rc.sysinit/umountroot and
+        * systemd depend on 'mount -o remount <mountpoint>' to work.
         */
        if (zfsutil && !strcmp(legacy, ZFS_MOUNTPOINT_LEGACY)) {
                (void) fprintf(stderr, gettext(
@@ -467,7 +467,7 @@ main(int argc, char **argv)
                return (MOUNT_USAGE);
        }
 
-       if (!zfsutil && strcmp(legacy, ZFS_MOUNTPOINT_LEGACY) && !remount_ro) {
+       if (!zfsutil && strcmp(legacy, ZFS_MOUNTPOINT_LEGACY) && !remount) {
                (void) fprintf(stderr, gettext(
                    "filesystem '%s' cannot be mounted using 'mount'.\n"
                    "Use 'zfs set mountpoint=%s' or 'zfs mount %s'.\n"