Btrfs: Add readonly snapshots support

Usage:

Set BTRFS_SUBVOL_RDONLY of btrfs_ioctl_vol_arg_v2->flags, and call
ioctl(BTRFS_I0CTL_SNAP_CREATE_V2).

Implementation:

- Set readonly bit of btrfs_root_item->flags.
- Add readonly checks in btrfs_permission (inode_permission),
btrfs_setattr, btrfs_set/remove_xattr and some ioctls.

Changelog for v3:

- Eliminate btrfs_root->readonly, but check btrfs_root->root_item.flags.
- Rename BTRFS_ROOT_SNAP_RDONLY to BTRFS_ROOT_SUBVOL_RDONLY.

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>

1 files changed, 8 insertions, 0 deletions

diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index f50e931fc217..29e30d832ec9 100644
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -910,6 +910,7 @@ static noinline int create_pending_snapshot(struct btrfs_trans_handle *trans,
         u64 to_reserve = 0;
         u64 index = 0;
         u64 objectid;
+        u64 root_flags;
 
         new_root_item = kmalloc(sizeof(*new_root_item), GFP_NOFS);
         if (!new_root_item) {
@@ -967,6 +968,13 @@ static noinline int create_pending_snapshot(struct btrfs_trans_handle *trans,
         btrfs_set_root_last_snapshot(&root->root_item, trans->transid);
         memcpy(new_root_item, &root->root_item, sizeof(*new_root_item));
 
+        root_flags = btrfs_root_flags(new_root_item);
+        if (pending->readonly)
+                root_flags |= BTRFS_ROOT_SUBVOL_RDONLY;
+        else
+                root_flags &= ~BTRFS_ROOT_SUBVOL_RDONLY;
+        btrfs_set_root_flags(new_root_item, root_flags);
+
         old = btrfs_lock_root_node(root);
         btrfs_cow_block(trans, root, old, NULL, 0, &old);
         btrfs_set_lock_blocking(old);