Re: [PATCH] btrfs: allow processes with cap_sys_resource to exceed quota

[Sargun Dhillon <sargun@sargun.me>]

What do you think about putting this behaviour behind a sysctl? Seems
better than to start introducing a new mechanism of marking tasks?

On Fri, Apr 21, 2017 at 6:05 AM, Adam Borowski <kilobyte@angband.pl> wrote:
> On Fri, Apr 21, 2017 at 10:09:46AM +0000, Sargun Dhillon wrote:
>> This patch allows processes with CAP_SYS_RESOURCE to exceed the qgroup
>> limit. 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.
>
>>  static bool qgroup_check_limits(const struct btrfs_qgroup *qg, u64 num_bytes)
>>  {
>> +     if (capable(CAP_SYS_RESOURCE))
>> +             return true;
>> +
>
> I don't think it's a good idea to make random root-uid processes ignore
> qgroups completely.  Just because the daemon in question doesn't use a
> separate uid is no reason to not protect you from it consuming all the disk
> space.
>
> A temporary request "please let me exceed limits" would make sense, though.
>
> The problem with CAP_SYS_RESOURCE is that it's always on unless explicitly
> dropped.
>
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