[RFC v2 PATCH 8/8] btrfs: add support for vfs_shift_uids and vfs_shift_gids mount options

[Djalal Harouni <tixxdz@gmail.com>]

Make btrfs able to parse vfs_shift_uids and vfs_shift_gids options and
set the appropriate flags into the super_block structure.

vfs_shift_uids and vfs_shift_gids allow mounts that show up in a mount
namespace that supports VFS UID/GID shifts on inodes to perform translation
from in kernel virtual view into on-disk view and vice versa. This
allows user namespaces users to be able to access, read and write inodes
on these mounts.

Signed-off-by: Dongsu Park <dongsu@endocode.com>
Signed-off-by: Djalal Harouni <tixxdz@opendz.org>
---
 fs/btrfs/super.c | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index 00b8f37..20e7223 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -304,7 +304,8 @@ enum {
 	Opt_commit_interval, Opt_barrier, Opt_nodefrag, Opt_nodiscard,
 	Opt_noenospc_debug, Opt_noflushoncommit, Opt_acl, Opt_datacow,
 	Opt_datasum, Opt_treelog, Opt_noinode_cache, Opt_usebackuproot,
-	Opt_nologreplay, Opt_norecovery,
+	Opt_nologreplay, Opt_norecovery, Opt_vfs_shift_uids,
+	Opt_vfs_shift_gids,
 #ifdef CONFIG_BTRFS_DEBUG
 	Opt_fragment_data, Opt_fragment_metadata, Opt_fragment_all,
 #endif
@@ -364,6 +365,8 @@ static const match_table_t tokens = {
 	{Opt_rescan_uuid_tree, "rescan_uuid_tree"},
 	{Opt_fatal_errors, "fatal_errors=%s"},
 	{Opt_commit_interval, "commit=%d"},
+	{Opt_vfs_shift_uids, "vfs_shift_uids"},
+	{Opt_vfs_shift_gids, "vfs_shift_gids"},
 #ifdef CONFIG_BTRFS_DEBUG
 	{Opt_fragment_data, "fragment=data"},
 	{Opt_fragment_metadata, "fragment=metadata"},
@@ -786,6 +789,12 @@ int btrfs_parse_options(struct btrfs_root *root, char *options,
 				info->commit_interval = BTRFS_DEFAULT_COMMIT_INTERVAL;
 			}
 			break;
+		case Opt_vfs_shift_uids:
+			root->fs_info->sb->s_iflags |= SB_I_VFS_SHIFT_UIDS;
+			break;
+		case Opt_vfs_shift_gids:
+			root->fs_info->sb->s_iflags |= SB_I_VFS_SHIFT_GIDS;
+			break;
 #ifdef CONFIG_BTRFS_DEBUG
 		case Opt_fragment_all:
 			btrfs_info(root->fs_info, "fragmenting all space");
@@ -1279,6 +1288,10 @@ static int btrfs_show_options(struct seq_file *seq, struct dentry *dentry)
 	if (btrfs_test_opt(root, FRAGMENT_METADATA))
 		seq_puts(seq, ",fragment=metadata");
 #endif
+	if (root->fs_info->sb->s_iflags & SB_I_VFS_SHIFT_UIDS)
+		seq_puts(seq, ",vfs_shift_uids");
+	if (root->fs_info->sb->s_iflags & SB_I_VFS_SHIFT_GIDS)
+		seq_puts(seq, ",vfs_shift_gids");
 	seq_printf(seq, ",subvolid=%llu",
 		  BTRFS_I(d_inode(dentry))->root->root_key.objectid);
 	seq_puts(seq, ",subvol=");
-- 
2.5.5