On 19.12.2017 12:45, Qu Wenruo wrote:
> btrfs_qgroup_inherit structure has two members, num_ref_copies and
> num_excl_copies, to info btrfs kernel modules to inherit (copy)
> rfer/excl numbers at snapshot/subvolume creation time.
>
> Since qgroup number is already hard to maintain for multi-level qgroup
> scenario, allowing user to manually manipulate qgroup inherit is quite
> easy to screw up qgroup numbers.
>
> Although btrfs-progs supports such inheritance specification, the
> options are hidden from user and not documented.
> So there is no need to allow user to manually specify inheritance in
> kernel.
>
> Reported-by: Nikolay Borisov <nbori...@suse.com>
> Signed-off-by: Qu Wenruo <w...@suse.com>
> ---
> The only concern is, currently we don't have good tool to handle
> inheritance of multi-level qgroups.
> The only method to get qgroup numbers correct is to run a quota rescan.
>
> So there may be some case where experienced (well, mostly a developer)
> user can use the hidden btrfs-progs options or manually craft an ioctl
> to handle multi-level qgroups without costly rescan.
> ---
> fs/btrfs/qgroup.c | 56
> ++++++++++++++--------------------------------
> include/uapi/linux/btrfs.h | 4 ++--
> 2 files changed, 19 insertions(+), 41 deletions(-)
>
> diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c
> index 168fd03ca3ac..d8a2413272f9 100644
> --- a/fs/btrfs/qgroup.c
> +++ b/fs/btrfs/qgroup.c
> @@ -2158,9 +2158,24 @@ int btrfs_qgroup_inherit(struct btrfs_trans_handle
> *trans,
> }
>
> if (inherit) {
> + /*
> + * num_excl/rfer_copies indicate how many qgroup pairs needs
> + * to be manually inherited (copy rfer or excl from src
> + * qgroup to dst)
> + *
> + * Allowing user to manipulate inheritance can easily cause
> + * problem in multi-level qgroup scenario.
> + * And the ioctl interface is hidden in btrfs-progs for a long
> + * time, deprecate them should not be a big problem.
> + */
> + if (inherit->__num_excl_copies || inherit->__num_ref_copies) {
> + ret = -ENOTTY;
> + btrfs_warn(fs_info,
> + "manually inherit excl/rfer is no longer supported");
> + goto out;
> + }
> i_qgroups = (u64 *)(inherit + 1);
> - nums = inherit->num_qgroups + 2 * inherit->num_ref_copies +
> - 2 * inherit->num_excl_copies;
> + nums = inherit->num_qgroups;
> for (i = 0; i < nums; ++i) {
> srcgroup = find_qgroup_rb(fs_info, *i_qgroups);
>
> @@ -2286,43 +2301,6 @@ int btrfs_qgroup_inherit(struct btrfs_trans_handle
> *trans,
> ++i_qgroups;
> }
>
> - for (i = 0; i < inherit->num_ref_copies; ++i, i_qgroups += 2) {
> - struct btrfs_qgroup *src;
> - struct btrfs_qgroup *dst;
> -
> - if (!i_qgroups[0] || !i_qgroups[1])
> - continue;
> -
> - src = find_qgroup_rb(fs_info, i_qgroups[0]);
> - dst = find_qgroup_rb(fs_info, i_qgroups[1]);
> -
> - if (!src || !dst) {
> - ret = -EINVAL;
> - goto unlock;
> - }
> -
> - dst->rfer = src->rfer - level_size;
> - dst->rfer_cmpr = src->rfer_cmpr - level_size;
> - }
> - for (i = 0; i < inherit->num_excl_copies; ++i, i_qgroups += 2) {
> - struct btrfs_qgroup *src;
> - struct btrfs_qgroup *dst;
> -
> - if (!i_qgroups[0] || !i_qgroups[1])
> - continue;
> -
> - src = find_qgroup_rb(fs_info, i_qgroups[0]);
> - dst = find_qgroup_rb(fs_info, i_qgroups[1]);
> -
> - if (!src || !dst) {
> - ret = -EINVAL;
> - goto unlock;
> - }
> -
> - dst->excl = src->excl + level_size;
> - dst->excl_cmpr = src->excl_cmpr + level_size;
> - }
> -
> unlock:
> spin_unlock(&fs_info->qgroup_lock);
> out:
> diff --git a/include/uapi/linux/btrfs.h b/include/uapi/linux/btrfs.h
> index ce615b75e855..099e088414d6 100644
> --- a/include/uapi/linux/btrfs.h
> +++ b/include/uapi/linux/btrfs.h
> @@ -80,8 +80,8 @@ struct btrfs_qgroup_limit {
> struct btrfs_qgroup_inherit {
> __u64 flags;
> __u64 num_qgroups;
> - __u64 num_ref_copies;
> - __u64 num_excl_copies;
> + __u64 __num_ref_copies; /* DEPRECATED */
> + __u64 __num_excl_copies; /* DEPRECATED */
I'd prefer we name them something even more generic i.e. :
pad1, pad2 or unused1, unused2 to really deter any efforts to use them.
I guess this could shouldn't have been merged in the first place ...
> struct btrfs_qgroup_limit lim;
> __u64 qgroups[0];
> };
>
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