On Tue, 02 Jun 2009 10:40:31 +0800 Li Zefan <lizf@xxxxxxxxxxxxxx> wrote:
> The 'noprefix' option was introduced for backwards-compatibility of
> cpuset, but actually it can be used when mounting other subsystems.
>
> This results in possibility of name collision, and now the collision
> can really happen, because we have 'stat' file in both memory and
> cpuacct subsystem:
>
> # mount -t cgroup -o noprefix,memory,cpuacct xxx /mnt
>
> Cgroup will happily mount the 2 subsystems, but only 'stat' file of
> memory subsys can be seen.
>
> We don't want users to use nopreifx, and also want to avoid name
> collision, so we change to allow noprefix only if mounting just
> the cpuset subsystem.
>
> ...
>
> diff --git a/kernel/cgroup.c b/kernel/cgroup.c
> index a7267bf..ad17f9d 100644
> --- a/kernel/cgroup.c
> +++ b/kernel/cgroup.c
> @@ -842,6 +842,11 @@ static int parse_cgroupfs_options(char *data,
> struct cgroup_sb_opts *opts)
> {
> char *token, *o = data ?: "all";
> + unsigned long mask = (unsigned long)-1;
> +
> +#ifdef CONFIG_CPUSETS
> + mask = ~(1 << cpuset_subsys_id);
> +#endif
This will actually produce the wrong result if cpuset_subsys_id >= 32.
You want 1UL here.
> opts->subsys_bits = 0;
> opts->flags = 0;
> @@ -886,6 +891,11 @@ static int parse_cgroupfs_options(char *data,
> }
> }
>
> + /* We allow noprefix only if mounting just the cpuset subsystem */
> + if (test_bit(ROOT_NOPREFIX, &opts->flags) &&
> + (opts->subsys_bits & mask))
> + return -EINVAL;
> +
uh, OK. I hope that comment is clear enough for anyone who wants to
understand it. It doesn't explain _why_ this is done..
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