Btrfs: Add BTRFS_IOC_SUBVOL_GETFLAGS/SETFLAGS ioctls

This allows us to set a snapshot or a subvolume readonly or writable
on the fly.

Usage:

Set BTRFS_SUBVOL_RDONLY of btrfs_ioctl_vol_arg_v2->flags, and then
call ioctl(BTRFS_IOCTL_SUBVOL_SETFLAGS);

Changelog for v3:

- Change to pass __u64 as ioctl parameter.

Changelog for v2:

- Add _GETFLAGS ioctl.
- Check if the passed fd is the root of a subvolume.
- Change the name from _SNAP_SETFLAGS to _SUBVOL_SETFLAGS.

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

2 files changed, 85 insertions, 0 deletions

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index f066ccb5dddf..ad1983524f97 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -1009,6 +1009,85 @@ out:
         return ret;
 }
 
+static noinline int btrfs_ioctl_subvol_getflags(struct file *file,
+                                                void __user *arg)
+{
+        struct inode *inode = fdentry(file)->d_inode;
+        struct btrfs_root *root = BTRFS_I(inode)->root;
+        int ret = 0;
+        u64 flags = 0;
+
+        if (inode->i_ino != BTRFS_FIRST_FREE_OBJECTID)
+                return -EINVAL;
+
+        down_read(&root->fs_info->subvol_sem);
+        if (btrfs_root_readonly(root))
+                flags |= BTRFS_SUBVOL_RDONLY;
+        up_read(&root->fs_info->subvol_sem);
+
+        if (copy_to_user(arg, &flags, sizeof(flags)))
+                ret = -EFAULT;
+
+        return ret;
+}
+
+static noinline int btrfs_ioctl_subvol_setflags(struct file *file,
+                                              void __user *arg)
+{
+        struct inode *inode = fdentry(file)->d_inode;
+        struct btrfs_root *root = BTRFS_I(inode)->root;
+        struct btrfs_trans_handle *trans;
+        u64 root_flags;
+        u64 flags;
+        int ret = 0;
+
+        if (root->fs_info->sb->s_flags & MS_RDONLY)
+                return -EROFS;
+
+        if (inode->i_ino != BTRFS_FIRST_FREE_OBJECTID)
+                return -EINVAL;
+
+        if (copy_from_user(&flags, arg, sizeof(flags)))
+                return -EFAULT;
+
+        if (flags & ~BTRFS_SUBVOL_CREATE_ASYNC)
+                return -EINVAL;
+
+        if (flags & ~BTRFS_SUBVOL_RDONLY)
+                return -EOPNOTSUPP;
+
+        down_write(&root->fs_info->subvol_sem);
+
+        /* nothing to do */
+        if (!!(flags & BTRFS_SUBVOL_RDONLY) == btrfs_root_readonly(root))
+                goto out;
+
+        root_flags = btrfs_root_flags(&root->root_item);
+        if (flags & BTRFS_SUBVOL_RDONLY)
+                btrfs_set_root_flags(&root->root_item,
+                                     root_flags | BTRFS_ROOT_SUBVOL_RDONLY);
+        else
+                btrfs_set_root_flags(&root->root_item,
+                                     root_flags & ~BTRFS_ROOT_SUBVOL_RDONLY);
+
+        trans = btrfs_start_transaction(root, 1);
+        if (IS_ERR(trans)) {
+                ret = PTR_ERR(trans);
+                goto out_reset;
+        }
+
+        ret = btrfs_update_root(trans, root,
+                                &root->root_key, &root->root_item);
+
+        btrfs_commit_transaction(trans, root);
+out_reset:
+        if (ret)
+                btrfs_set_root_flags(&root->root_item, root_flags);
+out:
+        up_write(&root->fs_info->subvol_sem);
+        return ret;
+}
+
 /*
  * helper to check if the subvolume references other subvolumes
  */
@@ -2282,6 +2361,10 @@ long btrfs_ioctl(struct file *file, unsigned int
                 return btrfs_ioctl_snap_create(file, argp, 1);
         case BTRFS_IOC_SNAP_DESTROY:
                 return btrfs_ioctl_snap_destroy(file, argp);
+        case BTRFS_IOC_SUBVOL_GETFLAGS:
+                return btrfs_ioctl_subvol_getflags(file, argp);
+        case BTRFS_IOC_SUBVOL_SETFLAGS:
+                return btrfs_ioctl_subvol_setflags(file, argp);
         case BTRFS_IOC_DEFAULT_SUBVOL:
                 return btrfs_ioctl_default_subvol(file, argp);
         case BTRFS_IOC_DEFRAG:
diff --git a/fs/btrfs/ioctl.h b/fs/btrfs/ioctl.h
index 52ae489974be..1223223351fa 100644
--- a/fs/btrfs/ioctl.h
+++ b/fs/btrfs/ioctl.h
@@ -194,4 +194,6 @@ struct btrfs_ioctl_space_args {
 #define BTRFS_IOC_WAIT_SYNC  _IOW(BTRFS_IOCTL_MAGIC, 22, __u64)
 #define BTRFS_IOC_SNAP_CREATE_V2 _IOW(BTRFS_IOCTL_MAGIC, 23, \
                                    struct btrfs_ioctl_vol_args_v2)
+#define BTRFS_IOC_SUBVOL_GETFLAGS _IOW(BTRFS_IOCTL_MAGIC, 25, __u64)
+#define BTRFS_IOC_SUBVOL_SETFLAGS _IOW(BTRFS_IOCTL_MAGIC, 26, __u64)
 #endif