Re: [PATCH 001/001] btrfs: Mechanism to modify the permission of a subvolume

[Filipe David Manana]

On Wed, Apr 23, 2014 at 2:28 PM, J S, Ajesh <ajesh.js@xxxxxx> wrote:
> From: Ajesh JS <ajesh.js@xxxxxx>
>
> This patch provides a mechanism to modify the permission of a subvolume in a btrfs file system
> This helps to apply a policy of having read-write subvolume inside a read-only subvolume.
> One use case is to have the whole root file system as a read-only subvolume and have /etc as a read-write subvolume inside.

Hi,

Why doesn't the existing properties feature (3.14) work for you?

Example:

$ mkfs.btrfs -f /dev/sdd
$ mount /dev/sdd /mnt/sdd

$ btrfs subvolume create /mnt/sdd/topsubvol
$ btrfs subvolume create /mnt/sdd/topsubvol/child

$ btrfs property set /mnt/sdd/topsubvol ro true

$ touch /mnt/sdd/topsubvol/file
$ touch: cannot touch â/mnt/sdd/topsubvol/fileâ: Read-only file system

$ touch /mnt/sdd/topsubvol/child/file

The property set/get just uses the ioctls BTRFS_IOC_SUBVOL_SETFLAGS
and BTRFS_IOC_SUBVOL_GETFLAGS.

thanks


>
> Signed-off-by: Ajesh JS <ajesh.js@xxxxxx>
> Reviewed-by: Liverance Fletcher <fletch@xxxxxx>; Clemenceau, <Matthieu matthieu.clemenceau@xxxxxx>
> "-------------------------------------------------------------------------"
> diff -rup linux-3.13.6/fs/btrfs/ioctl.c linux-3.13.6_btrfs/fs/btrfs/ioctl.c
> --- linux-3.13.6/fs/btrfs/ioctl.c       2014-03-07 11:37:02.000000000 +0530
> +++ linux-3.13.6_btrfs/fs/btrfs/ioctl.c 2014-03-19 14:25:28.375139699 +0530
> @@ -1636,6 +1636,68 @@ out:
>         return ret;
>  }
>
> +static noinline int btrfs_ioctl_subvol_modify(struct file *file,
> +                                               void __user *arg)
> +{
> +       struct btrfs_ioctl_vol_args_v2 *vol_args;
> +       struct inode *inode = file_inode(file);
> +       struct btrfs_root *root = BTRFS_I(inode)->root;
> +       struct btrfs_trans_handle *trans;
> +       u64 root_flags;
> +       u64 flags;
> +       int ret = 0;
> +
> +       ret = mnt_want_write_file(file);
> +       if (ret)
> +               goto out;
> +
> +       if (btrfs_ino(inode) != BTRFS_FIRST_FREE_OBJECTID) {
> +               ret = -EINVAL;
> +               goto out_drop_write;
> +       }
> +       vol_args = memdup_user(arg, sizeof(*vol_args));
> +       if (IS_ERR(vol_args))
> +               goto out_drop_write;
> +       vol_args->name[BTRFS_SUBVOL_NAME_MAX] = '\0';
> +       flags = vol_args->flags;
> +       if (!inode_owner_or_capable(inode)) {
> +               ret = -EACCES;
> +               goto out_drop_write;
> +       }
> +
> +       down_write(&root->fs_info->subvol_sem);
> +       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);
> +               printk(KERN_INFO "Setting %s to ro\n", vol_args->name);
> +       } else {
> +               btrfs_set_root_flags(&root->root_item,
> +                                       root_flags & ~BTRFS_ROOT_SUBVOL_RDONLY);
> +               printk(KERN_INFO "Setting %s to rw\n", vol_args->name);
> +       }
> +
> +       trans = btrfs_start_transaction(root, 1);
> +       if (IS_ERR(trans)) {
> +               ret = PTR_ERR(trans);
> +               goto out_reset;
> +       }
> +
> +       ret = btrfs_update_root(trans, root->fs_info->tree_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);
> +       up_write(&root->fs_info->subvol_sem);
> +out_drop_write:
> +       mnt_drop_write_file(file);
> +out:
> +       return ret;
> +}
> +
>  static noinline int btrfs_ioctl_subvol_getflags(struct file *file,
>                                                 void __user *arg)
>  {
> @@ -4509,6 +4571,8 @@ long btrfs_ioctl(struct file *file, unsi
>                 return btrfs_ioctl_snap_create(file, argp, 1);
>         case BTRFS_IOC_SUBVOL_CREATE_V2:
>                 return btrfs_ioctl_snap_create_v2(file, argp, 1);
> +       case BTRFS_IOC_SUBVOL_MODIFY:
> +               return btrfs_ioctl_subvol_modify(file, argp);
>         case BTRFS_IOC_SNAP_DESTROY:
>                 return btrfs_ioctl_snap_destroy(file, argp);
>         case BTRFS_IOC_SUBVOL_GETFLAGS:
> diff -rup linux-3.13.6/include/uapi/linux/btrfs.h linux-3.13.6_btrfs/include/uapi/linux/btrfs.h
> --- linux-3.13.6/include/uapi/linux/btrfs.h     2014-03-07 11:37:02.000000000 +0530
> +++ linux-3.13.6_btrfs/include/uapi/linux/btrfs.h       2014-03-19 15:34:30.648255239 +0530
> @@ -606,5 +606,7 @@ static inline char *btrfs_err_str(enum b
>                                     struct btrfs_ioctl_dev_replace_args)
>  #define BTRFS_IOC_FILE_EXTENT_SAME _IOWR(BTRFS_IOCTL_MAGIC, 54, \
>                                          struct btrfs_ioctl_same_args)
> +#define BTRFS_IOC_SUBVOL_MODIFY _IOW(BTRFS_IOCTL_MAGIC, 55, \
> +                                  struct btrfs_ioctl_vol_args_v2)
>
>  #endif /* _UAPI_LINUX_BTRFS_H */
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-- 
Filipe David Manana,

"Reasonable men adapt themselves to the world.
 Unreasonable men adapt the world to themselves.
 That's why all progress depends on unreasonable men."
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