GFS2: Fix -o meta mounts for subsequent mounts (i.e. all but the first one)

We have a long term plan to use the "-o meta" flag to GFS2 mounts to
access the alternate root which is used to store metadata for a GFS2
filesystem. This will allow us to eventually remove support for the
gfs2meta filesystem type (which is in any case just a "front end" to
the gfs2 filesystem type with the meta/master root).

Currently the "-o meta" option is only taken into account on the
initial mount of the filesystem. Subsequent mounts of the same
filesystem (i.e. on the same device) result in basically the same
as bind mounting the root of the original mount.

This patch changes that by using what is more or less a copy
of get_sb_bdev() and extending it so that it will take into
account the alternate root in all cases. The main difference
is that we have to parse the mount options a bit earlier. We can
then use them to select the appropriate root towards the end of
the function.

In addition this also fixes a bug where it was possible (but certainly
not desirable) to set different ro/rw options for the meta root
when mounted via the gfs2meta fs compared with the original mount.

Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>
Cc: Alexander Viro <aviro@redhat.com>

3 files changed, 127 insertions, 26 deletions

diff --git a/fs/gfs2/ops_fstype.c b/fs/gfs2/ops_fstype.c
index 52fb6c048981..e5ee06231ae5 100644
--- a/fs/gfs2/ops_fstype.c
+++ b/fs/gfs2/ops_fstype.c
@@ -1114,7 +1114,7 @@ void gfs2_online_uevent(struct gfs2_sbd *sdp)
  * Returns: errno
  */
 
-static int fill_super(struct super_block *sb, void *data, int silent)
+static int fill_super(struct super_block *sb, struct gfs2_args *args, int silent)
 {
 	struct gfs2_sbd *sdp;
 	struct gfs2_holder mount_gh;
@@ -1125,17 +1125,7 @@ static int fill_super(struct super_block *sb, void *data, int silent)
 		printk(KERN_WARNING "GFS2: can't alloc struct gfs2_sbd\n");
 		return -ENOMEM;
 	}
-
-	sdp->sd_args.ar_quota = GFS2_QUOTA_DEFAULT;
-	sdp->sd_args.ar_data = GFS2_DATA_DEFAULT;
-	sdp->sd_args.ar_commit = 60;
-	sdp->sd_args.ar_errors = GFS2_ERRORS_DEFAULT;
-
-	error = gfs2_mount_args(sdp, &sdp->sd_args, data);
-	if (error) {
-		printk(KERN_WARNING "GFS2: can't parse mount arguments\n");
-		goto fail;
-	}
+	sdp->sd_args = *args;
 
 	if (sdp->sd_args.ar_spectator) {
                 sb->s_flags |= MS_RDONLY;
@@ -1243,18 +1233,125 @@ fail:
 	return error;
 }
 
-static int gfs2_get_sb(struct file_system_type *fs_type, int flags,
-		       const char *dev_name, void *data, struct vfsmount *mnt)
+static int set_gfs2_super(struct super_block *s, void *data)
 {
-	return get_sb_bdev(fs_type, flags, dev_name, data, fill_super, mnt);
+	s->s_bdev = data;
+	s->s_dev = s->s_bdev->bd_dev;
+
+	/*
+	 * We set the bdi here to the queue backing, file systems can
+	 * overwrite this in ->fill_super()
+	 */
+	s->s_bdi = &bdev_get_queue(s->s_bdev)->backing_dev_info;
+	return 0;
 }
 
-static int test_meta_super(struct super_block *s, void *ptr)
+static int test_gfs2_super(struct super_block *s, void *ptr)
 {
 	struct block_device *bdev = ptr;
 	return (bdev == s->s_bdev);
 }
 
+/**
+ * gfs2_get_sb - Get the GFS2 superblock
+ * @fs_type: The GFS2 filesystem type
+ * @flags: Mount flags
+ * @dev_name: The name of the device
+ * @data: The mount arguments
+ * @mnt: The vfsmnt for this mount
+ *
+ * Q. Why not use get_sb_bdev() ?
+ * A. We need to select one of two root directories to mount, independent
+ *    of whether this is the initial, or subsequent, mount of this sb
+ *
+ * Returns: 0 or -ve on error
+ */
+
+static int gfs2_get_sb(struct file_system_type *fs_type, int flags,
+		       const char *dev_name, void *data, struct vfsmount *mnt)
+{
+	struct block_device *bdev;
+	struct super_block *s;
+	fmode_t mode = FMODE_READ;
+	int error;
+	struct gfs2_args args;
+	struct gfs2_sbd *sdp;
+
+	if (!(flags & MS_RDONLY))
+		mode |= FMODE_WRITE;
+
+	bdev = open_bdev_exclusive(dev_name, mode, fs_type);
+	if (IS_ERR(bdev))
+		return PTR_ERR(bdev);
+
+	/*
+	 * once the super is inserted into the list by sget, s_umount
+	 * will protect the lockfs code from trying to start a snapshot
+	 * while we are mounting
+	 */
+	mutex_lock(&bdev->bd_fsfreeze_mutex);
+	if (bdev->bd_fsfreeze_count > 0) {
+		mutex_unlock(&bdev->bd_fsfreeze_mutex);
+		error = -EBUSY;
+		goto error_bdev;
+	}
+	s = sget(fs_type, test_gfs2_super, set_gfs2_super, bdev);
+	mutex_unlock(&bdev->bd_fsfreeze_mutex);
+	error = PTR_ERR(s);
+	if (IS_ERR(s))
+		goto error_bdev;
+
+	memset(&args, 0, sizeof(args));
+	args.ar_quota = GFS2_QUOTA_DEFAULT;
+	args.ar_data = GFS2_DATA_DEFAULT;
+	args.ar_commit = 60;
+	args.ar_errors = GFS2_ERRORS_DEFAULT;
+
+	error = gfs2_mount_args(&args, data);
+	if (error) {
+		printk(KERN_WARNING "GFS2: can't parse mount arguments\n");
+		if (s->s_root)
+			goto error_super;
+		deactivate_locked_super(s);
+		return error;
+	}
+
+	if (s->s_root) {
+		error = -EBUSY;
+		if ((flags ^ s->s_flags) & MS_RDONLY)
+			goto error_super;
+		close_bdev_exclusive(bdev, mode);
+	} else {
+		char b[BDEVNAME_SIZE];
+
+		s->s_flags = flags;
+		s->s_mode = mode;
+		strlcpy(s->s_id, bdevname(bdev, b), sizeof(s->s_id));
+		sb_set_blocksize(s, block_size(bdev));
+		error = fill_super(s, &args, flags & MS_SILENT ? 1 : 0);
+		if (error) {
+			deactivate_locked_super(s);
+			return error;
+		}
+		s->s_flags |= MS_ACTIVE;
+		bdev->bd_super = s;
+	}
+
+	sdp = s->s_fs_info;
+	mnt->mnt_sb = s;
+	if (args.ar_meta)
+		mnt->mnt_root = dget(sdp->sd_master_dir);
+	else
+		mnt->mnt_root = dget(sdp->sd_root_dir);
+	return 0;
+
+error_super:
+	deactivate_locked_super(s);
+error_bdev:
+	close_bdev_exclusive(bdev, mode);
+	return error;
+}
+
 static int set_meta_super(struct super_block *s, void *ptr)
 {
 	return -EINVAL;
@@ -1274,13 +1371,17 @@ static int gfs2_get_sb_meta(struct file_system_type *fs_type, int flags,
 		       dev_name, error);
 		return error;
 	}
-	s = sget(&gfs2_fs_type, test_meta_super, set_meta_super,
+	s = sget(&gfs2_fs_type, test_gfs2_super, set_meta_super,
 		 path.dentry->d_inode->i_sb->s_bdev);
 	path_put(&path);
 	if (IS_ERR(s)) {
 		printk(KERN_WARNING "GFS2: gfs2 mount does not exist\n");
 		return PTR_ERR(s);
 	}
+	if ((flags ^ s->s_flags) & MS_RDONLY) {
+		deactivate_locked_super(s);
+		return -EBUSY;
+	}
 	sdp = s->s_fs_info;
 	mnt->mnt_sb = s;
 	mnt->mnt_root = dget(sdp->sd_master_dir);
diff --git a/fs/gfs2/super.c b/fs/gfs2/super.c
index 0ec3ec672de1..42e5458703f0 100644
--- a/fs/gfs2/super.c
+++ b/fs/gfs2/super.c
@@ -106,13 +106,13 @@ static const match_table_t tokens = {
 
 /**
  * gfs2_mount_args - Parse mount options
- * @sdp:
- * @data:
+ * @args: The structure into which the parsed options will be written
+ * @options: The options to parse
  *
  * Return: errno
  */
 
-int gfs2_mount_args(struct gfs2_sbd *sdp, struct gfs2_args *args, char *options)
+int gfs2_mount_args(struct gfs2_args *args, char *options)
 {
 	char *o;
 	int token;
@@ -157,7 +157,7 @@ int gfs2_mount_args(struct gfs2_sbd *sdp, struct gfs2_args *args, char *options)
 			break;
 		case Opt_debug:
 			if (args->ar_errors == GFS2_ERRORS_PANIC) {
-				fs_info(sdp, "-o debug and -o errors=panic "
+				printk(KERN_WARNING "GFS2: -o debug and -o errors=panic "
 				       "are mutually exclusive.\n");
 				return -EINVAL;
 			}
@@ -210,7 +210,7 @@ int gfs2_mount_args(struct gfs2_sbd *sdp, struct gfs2_args *args, char *options)
 		case Opt_commit:
 			rv = match_int(&tmp[0], &args->ar_commit);
 			if (rv || args->ar_commit <= 0) {
-				fs_info(sdp, "commit mount option requires a positive numeric argument\n");
+				printk(KERN_WARNING "GFS2: commit mount option requires a positive numeric argument\n");
 				return rv ? rv : -EINVAL;
 			}
 			break;
@@ -219,7 +219,7 @@ int gfs2_mount_args(struct gfs2_sbd *sdp, struct gfs2_args *args, char *options)
 			break;
 		case Opt_err_panic:
 			if (args->ar_debug) {
-				fs_info(sdp, "-o debug and -o errors=panic "
+				printk(KERN_WARNING "GFS2: -o debug and -o errors=panic "
 					"are mutually exclusive.\n");
 				return -EINVAL;
 			}
@@ -227,7 +227,7 @@ int gfs2_mount_args(struct gfs2_sbd *sdp, struct gfs2_args *args, char *options)
 			break;
 		case Opt_error:
 		default:
-			fs_info(sdp, "invalid mount option: %s\n", o);
+			printk(KERN_WARNING "GFS2: invalid mount option: %s\n", o);
 			return -EINVAL;
 		}
 	}
@@ -1062,7 +1062,7 @@ static int gfs2_remount_fs(struct super_block *sb, int *flags, char *data)
 	spin_lock(&gt->gt_spin);
 	args.ar_commit = gt->gt_log_flush_secs;
 	spin_unlock(&gt->gt_spin);
-	error = gfs2_mount_args(sdp, &args, data);
+	error = gfs2_mount_args(&args, data);
 	if (error)
 		return error;
 
diff --git a/fs/gfs2/super.h b/fs/gfs2/super.h
index 235db3682885..ed962ea68c3a 100644
--- a/fs/gfs2/super.h
+++ b/fs/gfs2/super.h
@@ -27,7 +27,7 @@ static inline unsigned int gfs2_jindex_size(struct gfs2_sbd *sdp)
 
 extern void gfs2_jindex_free(struct gfs2_sbd *sdp);
 
-extern int gfs2_mount_args(struct gfs2_sbd *sdp, struct gfs2_args *args, char *data);
+extern int gfs2_mount_args(struct gfs2_args *args, char *data);
 
 extern struct gfs2_jdesc *gfs2_jdesc_find(struct gfs2_sbd *sdp, unsigned int jid);
 extern int gfs2_jdesc_check(struct gfs2_jdesc *jd);