于 2013/4/26 3:39, David Shwatrz 写道:
> Hello,
>
> I have a question about cgroup implementation:
>
> The /sys/fs/cgroup entry is created in kernel/cgroup.c:
>
> static struct kobject *cgroup_kobj;
>
> cgroup_init(void) {
> ...
> cgroup_kobj = kobject_create_and_add("cgroup", fs_kobj);
> if (!cgroup_kobj) {
> err = -ENOMEM;
> goto out;
> }
>
> }
>
> I wondered about this two points:
> 1) why is the /sys/fs/cgroup entry created at all?
> 2) why is this done as a sysfs entry.
>
> The cgroup_kobj is not used anywhere in this module apart from
> its creation above (and destroying if we later fail with
> register_filesystem() in this same method). I don't see anywhere usage
> of syfs API to create files underneath
> it. In fact, the entries beneath it are created by mkdir of admin or
> systemd code. so what's the point of it being a sysfs entry ? wouldn't
> simply mkdir be ok ? and why under /sys/fs?
>
> Since cgroups can be mounted by definition on every path, why this is needed?
>
It's supposed to be the standard place to mount cgroupfs.
commit 676db4af043014e852f67ba0349dae0071bd11f3
Author: Greg KH <gregkh@xxxxxxx>
Date: Thu Aug 5 13:53:35 2010 -0700
cgroupfs: create /sys/fs/cgroup to mount cgroupfs on
We really shouldn't be asking userspace to create new root filesystems.
So follow along with all of the other in-kernel filesystems, and provide
a mount point in sysfs.
For cgroupfs, this should be in /sys/fs/cgroup/ This change provides
that mount point when the cgroup filesystem is registered in the kernel.
Acked-by: Paul Menage <menage@xxxxxxxxxx>
Acked-by: Dhaval Giani <dhaval.giani@xxxxxxxxx>
Cc: Li Zefan <lizf@xxxxxxxxxxxxxx>
Cc: Lennart Poettering <lennart@xxxxxxxxxxxxxx>
Cc: Kay Sievers <kay.sievers@xxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>
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