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    SubjectRe: [PATCH 2/2] devscgroup: relax task to dev_cgroup conversion
    On Wed, Jun 4, 2008 at 12:39 AM, Pavel Emelyanov <xemul@openvz.org> wrote:
    > Two functions, that need to get a device_cgroup from a task (they
    > are devcgroup_inode_permission and devcgroup_inode_mknod) make it
    > in a strange way:
    >
    > They get a css_set from task, then a subsys_state from css_set,
    > then a cgroup from the state and then a subsys_state again from
    > the cgroup. Besides, the devices_subsys_id is read from memory,
    > whilst there's a enum-ed constant for it.
    >
    > Optimize this part a bit:
    > 1. Get the subsys_stats form the task and be done - no 2 extra
    > dereferences,
    > 2. Use the device_subsys_id constant, not the value from memory
    > (i.e. one less dereference).
    >
    > Found while preparing 2.6.26 OpenVZ port.
    >
    > Signed-off-by: Pavel Emelyanov <xemul@openvz.org>

    Acked-by: Paul Menage <menage@google.com>

    Yes, that's more how the css_set pointers are meant to be used. Maybe
    improve it further by extracting a task_to_devcgroup() inline
    function?

    Paul

    >
    > ---
    > security/device_cgroup.c | 10 ++++------
    > 1 files changed, 4 insertions(+), 6 deletions(-)
    >
    > diff --git a/security/device_cgroup.c b/security/device_cgroup.c
    > index 15f2f80..f9941a7 100644
    > --- a/security/device_cgroup.c
    > +++ b/security/device_cgroup.c
    > @@ -506,7 +506,6 @@ struct cgroup_subsys devices_subsys = {
    >
    > int devcgroup_inode_permission(struct inode *inode, int mask)
    > {
    > - struct cgroup *cgroup;
    > struct dev_cgroup *dev_cgroup;
    > struct dev_whitelist_item *wh;
    >
    > @@ -515,8 +514,8 @@ int devcgroup_inode_permission(struct inode *inode, int mask)
    > return 0;
    > if (!S_ISBLK(inode->i_mode) && !S_ISCHR(inode->i_mode))
    > return 0;
    > - cgroup = task_cgroup(current, devices_subsys.subsys_id);
    > - dev_cgroup = cgroup_to_devcgroup(cgroup);
    > + dev_cgroup = css_to_devcgroup(task_subsys_state(current,
    > + devices_subsys_id));
    > if (!dev_cgroup)
    > return 0;
    >
    > @@ -547,12 +546,11 @@ acc_check:
    >
    > int devcgroup_inode_mknod(int mode, dev_t dev)
    > {
    > - struct cgroup *cgroup;
    > struct dev_cgroup *dev_cgroup;
    > struct dev_whitelist_item *wh;
    >
    > - cgroup = task_cgroup(current, devices_subsys.subsys_id);
    > - dev_cgroup = cgroup_to_devcgroup(cgroup);
    > + dev_cgroup = css_to_devcgroup(task_subsys_state(current,
    > + devices_subsys_id));
    > if (!dev_cgroup)
    > return 0;
    >
    > --
    > 1.5.3.4
    >
    >


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