On Fri, Apr 21, 2017 at 11:12:47PM +0000, Sargun Dhillon wrote:
> This patch introduces the quota override flag to btrfs_fs_info, and
> a change to quota limit checking code to temporarily allow for quota
> to be overridden for processes with cap_sys_resource.
>
> It's useful for administrative programs, such as log rotation,
> that may need to temporarily use more disk space in order to free up
> a greater amount of overall disk space without yielding more disk
> space to the rest of userland.
>
> Eventually, we may want to add the idea of an operator-specific
> quota, operator reserved space, or something else to allow for
> administrative override, but this is perhaps the simplest
> solution.
>
> Signed-off-by: Sargun Dhillon <sar...@sargun.me>
> ---
> fs/btrfs/ctree.h | 3 +++
> fs/btrfs/qgroup.c | 9 +++++++--
> 2 files changed, 10 insertions(+), 2 deletions(-)
>
> diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
> index c411590..01a095b 100644
> --- a/fs/btrfs/ctree.h
> +++ b/fs/btrfs/ctree.h
> @@ -1098,6 +1098,9 @@ struct btrfs_fs_info {
> u32 nodesize;
> u32 sectorsize;
> u32 stripesize;
> +
> + /* Allow tasks with cap_sys_resource to override the quota */
> + bool quota_override;
As mentioned, please define bitmask for the existing on-disk flags,
add a new one
#define BTRFS_QGROUP_OVERRIDE_LIMITS (1ULL << 32)
and modify update_qgroup_status_item to use the bitmask.
> };
>
> static inline struct btrfs_fs_info *btrfs_sb(struct super_block *sb)
> diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c
> index a59801d..0328492 100644
> --- a/fs/btrfs/qgroup.c
> +++ b/fs/btrfs/qgroup.c
> @@ -2347,8 +2347,12 @@ int btrfs_qgroup_inherit(struct btrfs_trans_handle
> *trans,
> return ret;
> }
>
> -static bool qgroup_check_limits(const struct btrfs_qgroup *qg, u64 num_bytes)
> +static bool qgroup_check_limits(const struct btrfs_qgroup *qg,
> + u64 num_bytes, bool quota_override)
> {
> + if (quota_override && capable(CAP_SYS_RESOURCE))
> + return true;
> +
> if ((qg->lim_flags & BTRFS_QGROUP_LIMIT_MAX_RFER) &&
> qg->reserved + (s64)qg->rfer + num_bytes > qg->max_rfer)
> return false;
> @@ -2366,6 +2370,7 @@ static int qgroup_reserve(struct btrfs_root *root, u64
> num_bytes, bool enforce)
> struct btrfs_qgroup *qgroup;
> struct btrfs_fs_info *fs_info = root->fs_info;
> u64 ref_root = root->root_key.objectid;
> + bool qo = fs_info->quota_override;
> int ret = 0;
> struct ulist_node *unode;
> struct ulist_iterator uiter;
> @@ -2401,7 +2406,7 @@ static int qgroup_reserve(struct btrfs_root *root, u64
> num_bytes, bool enforce)
>
> qg = unode_aux_to_qgroup(unode);
>
> - if (enforce && !qgroup_check_limits(qg, num_bytes)) {
> + if (enforce && !qgroup_check_limits(qg, num_bytes, qo)) {
I suggest to put the override check as a separate condition, no need to
pass it down to qgroup_check_limits.
> ret = -EDQUOT;
> goto out;
> }
> --
> 2.9.3
>
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