From b83cc9693f39689490970c19f6c5b866f6719a70 Mon Sep 17 00:00:00 2001
From: Li Zefan <lizf@cn.fujitsu.com>
Date: Mon, 20 Dec 2010 16:04:08 +0800
Subject: [PATCH] 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>
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