linux-kernel - Re: [PATCH 1/4] Support named cgroups hierarchies

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Date:	Wed, 22 Jul 2009 23:27:23 -0700
From:	Paul Menage <menage@...gle.com>
To:	Li Zefan <lizf@...fujitsu.com>
Cc:	akpm@...ux-foundation.org, containers@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/4] Support named cgroups hierarchies

On Wed, Jul 22, 2009 at 11:20 PM, Li Zefan<lizf@...fujitsu.com> wrote:
>> +The name should match [\w.-]+
>> +
>
> "[\w._-]+" ?
>
> But I double we need to check this.

\w includes '_'

>>  static int cgroup_set_super(struct super_block *sb, void *data)
>>  {
>>       int ret;
>> -     struct cgroupfs_root *root = data;
>> +     struct cgroup_sb_opts *opts = data;
>> +
>> +     /* If we don't have a new root, we can't set up a new sb */
>> +     if (!opts->new_root)
>> +             return -EINVAL;
>> +
>
> I think this should be BUG_ON(). If set_super() is called,
> we are allocating a new root, so opts->new_root won't be NULL.

Not true - if you try to mount a hierarchy by name, but with no
subsystem options, then we don't construct a new root, but we still
call sget(). If we find a superblock with the right name then we use
it, else sget() will allocate a new superblock and call
cgroup_set_super(), at which point we need to fail.

>
>> +             struct cgroupfs_root *new_root = cgroup_root_from_opts(&opts);
>
> Why not just declare new_root in the beginning of cgroup_get_sb()?

Because it's not needed for the entire scope of the function. Keeping
its scope as small as possible makes it clearer what it's being used
for.

Paul
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