Btrfs: Add mount into directory support

Modified form of original patch from Christoph Hellwig to make btrfs
mount into the default subvolume by default.

mount /dev/somedevice:subvolumename to get other subvolumes or
mount /dev/somedevice:. to get the root

Signed-off-by: Chris Mason <chris.mason@oracle.com>

diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index a68101ae1a3b600f10b9286b5e867f30f00227e8..8a94be1a773b08ce1f2cd9a970f2a973d3bd91ec 100644 (file)
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -16,6 +16,7 @@
  * Boston, MA 021110-1307, USA.
  */
 
+#include <linux/blkdev.h>
 #include <linux/module.h>
 #include <linux/buffer_head.h>
 #include <linux/fs.h>
@@ -26,6 +27,7 @@
 #include <linux/string.h>
 #include <linux/smp_lock.h>
 #include <linux/backing-dev.h>
+#include <linux/mount.h>
 #include <linux/mpage.h>
 #include <linux/swap.h>
 #include <linux/writeback.h>
@@ -145,11 +147,126 @@ static void btrfs_write_super(struct super_block *sb)
        sb->s_dirt = 0;
 }
 
+/*
+ * This is almost a copy of get_sb_bdev in fs/super.c.
+ * We need the local copy to allow direct mounting of
+ * subvolumes, but this could be easily integrated back
+ * into the generic version.  --hch
+ */
+
+/* start copy & paste */
+static int set_bdev_super(struct super_block *s, void *data)
+{
+       s->s_bdev = data;
+       s->s_dev = s->s_bdev->bd_dev;
+       return 0;
+}
+
+static int test_bdev_super(struct super_block *s, void *data)
+{
+       return (void *)s->s_bdev == data;
+}
+
+int btrfs_get_sb_bdev(struct file_system_type *fs_type,
+       int flags, const char *dev_name, void *data,
+       int (*fill_super)(struct super_block *, void *, int),
+       struct vfsmount *mnt, const char *subvol)
+{
+       struct block_device *bdev = NULL;
+       struct super_block *s;
+       struct dentry *root;
+       int error = 0;
+
+       bdev = open_bdev_excl(dev_name, flags, 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
+        */
+       down(&bdev->bd_mount_sem);
+       s = sget(fs_type, test_bdev_super, set_bdev_super, bdev);
+       up(&bdev->bd_mount_sem);
+       if (IS_ERR(s))
+               goto error_s;
+
+       if (s->s_root) {
+               if ((flags ^ s->s_flags) & MS_RDONLY) {
+                       up_write(&s->s_umount);
+                       deactivate_super(s);
+                       error = -EBUSY;
+                       goto error_bdev;
+               }
+
+               close_bdev_excl(bdev);
+       } else {
+               char b[BDEVNAME_SIZE];
+
+               s->s_flags = flags;
+               strlcpy(s->s_id, bdevname(bdev, b), sizeof(s->s_id));
+               sb_set_blocksize(s, block_size(bdev));
+               error = fill_super(s, data, flags & MS_SILENT ? 1 : 0);
+               if (error) {
+                       up_write(&s->s_umount);
+                       deactivate_super(s);
+                       goto error;
+               }
+
+               s->s_flags |= MS_ACTIVE;
+       }
+
+       if (subvol) {
+               root = lookup_one_len(subvol, s->s_root, strlen(subvol));
+               if (IS_ERR(root)) {
+                       up_write(&s->s_umount);
+                       deactivate_super(s);
+                       error = PTR_ERR(root);
+                       goto error;
+               }
+               if (!root->d_inode) {
+                       dput(root);
+                       up_write(&s->s_umount);
+                       deactivate_super(s);
+                       error = -ENXIO;
+                       goto error;
+               }
+       } else {
+               root = dget(s->s_root);
+       }
+
+       mnt->mnt_sb = s;
+       mnt->mnt_root = root;
+       return 0;
+
+error_s:
+       error = PTR_ERR(s);
+error_bdev:
+       close_bdev_excl(bdev);
+error:
+       return error;
+}
+/* end copy & paste */
+
 static int btrfs_get_sb(struct file_system_type *fs_type,
-       int flags, const char *dev_name, void *data, struct vfsmount *mnt)
+       int flags, const char *identifier, void *data, struct vfsmount *mnt)
 {
-       return get_sb_bdev(fs_type, flags, dev_name, data,
-                          btrfs_fill_super, mnt);
+       int ret;
+       char *_identifier = kstrdup(identifier, GFP_KERNEL);
+       char *subvol_name;
+       const char *dev_name;
+
+       subvol_name = _identifier;
+       dev_name = strsep(&subvol_name, ":");
+       if (!dev_name)
+               return -ENOMEM;
+
+       ret = btrfs_get_sb_bdev(fs_type, flags, dev_name, data,
+                       btrfs_fill_super, mnt,
+                       subvol_name ? subvol_name : "default");
+       kfree(_identifier);
+       return ret;
 }
 
 static int btrfs_statfs(struct dentry *dentry, struct kstatfs *buf)