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    SubjectRe: [RFC][PATCH] taskstats: Fix CGROUPSTATS_TYPE_CGROUP_STATS having same value as TASKSTATS_TYPE_PID
    Date
    On Monday 13 July 2009 21:23:10 Balbir Singh wrote:
    > * Nikanth Karthikesan <knikanth@suse.de> [2009-07-13 21:07:37]:
    > > On Monday 13 July 2009 19:11:58 Balbir Singh wrote:
    > > > * Nikanth Karthikesan <knikanth@suse.de> [2009-07-13 18:31:12]:
    > > > > Hi
    > > > >
    > > > > Currently we never get message from kernel to userspace of type
    > > > > TASKSTATS_TYPE_PID. Otherwise this could have been spotted earlier.
    > > > >
    > > > > I was trying to add a new taskstat command that would return response
    > > > > of type TASKSTATS_TYPE_PID.
    > > > >
    > > > > Having the same values would restrict one not to use the same netlink
    > > > > socket for a command that would return response of type
    > > > > TASKSTATS_TYPE_PID and the CGROUPSTATS_CMD_GET command.
    > > > >
    > > > > Should we fix it by using values after __TASKSTATS_TYPE_MAX.
    > > > >
    > > > > Changing this now might break pre-built binaries. Or is this
    > > > > intended, and the application is not supposed to use CGROUPSTATS and
    > > > > TASKSTATS on the same socket?
    > > >
    > > > Ideally they are supposed to be on different sockets, but nothing
    > > > really is hard and fast in terms of rules.
    > >
    > > IMHO, If we are adding CGROUPSTATS_CMD_GET to the same netlink family of
    > > TASKSTATS, we should allow both the commands in the same socket.
    > >
    > > > > Thanks
    > > > > Nikanth
    > > > >
    > > > > Currently we never get message from kernel to userspace of type
    > > > > TASKSTATS_TYPE_PID. Otherwise this could have been spotted earlier.
    > > > > Having the values in the same range would restrict one not to use the
    > > > > same netlink socket for a command that would return response of type
    > > > > TASKSTATS_TYPE_PID and the CGROUPSTATS_CMD_GET command. Fix it by
    > > > > using values after
    > > > > __TASKSTATS_TYPE_MAX.
    > > > >
    > > > > Signed-off-by: Nikanth Karthikesan <knikanth@suse.de>
    > > > >
    > > > > ---
    > > > >
    > > > >
    > > > > diff --git a/include/linux/cgroupstats.h
    > > > > b/include/linux/cgroupstats.h index 3753c33..87b31f0 100644
    > > > > --- a/include/linux/cgroupstats.h
    > > > > +++ b/include/linux/cgroupstats.h
    > > > > @@ -53,7 +53,7 @@ enum {
    > > > > #define CGROUPSTATS_CMD_MAX (__CGROUPSTATS_CMD_MAX - 1)
    > > > >
    > > > > enum {
    > > > > - CGROUPSTATS_TYPE_UNSPEC = 0, /* Reserved */
    > > > > + CGROUPSTATS_TYPE_UNSPEC = __TASKSTATS_TYPE_MAX, /* Reserved */
    > > > > CGROUPSTATS_TYPE_CGROUP_STATS, /* contains name + stats */
    > > > > __CGROUPSTATS_TYPE_MAX,
    > > > > };
    > > >
    > > > This seems like the correct fix
    > > >
    > > > Reviewed-by: Balbir Singh <balbir@linux.vnet.ibm.com>
    > >
    > > But this would break applications every time a new item is added to the
    > > enums in taskstat.h
    >
    > Yes, correct and the expectation, we will bump the version number (see
    > version field) or ignore the fix and send a strong recommendation that
    > we should use different sockets for cgroupstats and taskstats.
    >
    > > The correct fix would be to add all the CGROUPSTATS_* enums, as part of
    > > the same enum in taskstat.h. So that when new members are added to enum's
    > > in taskstat.h, the cgroup stat enum's values won't change and
    > > applications need not be re-built. If you agree, I would send a patch to
    > > do that.
    >
    > I wanted to keep the separate to avoid #ifdef's around the code. One
    > other generic fix would be to use different starting bases. We could
    > for example use a bit (say bit 63) to indicate the type - taskstats or
    > cgroupstats, but we might be too late for that.
    >
    > Please remember to bump the version field, lets try your suggested
    > approach of integration and if that can be done cleanly, I have no
    > objection.

    I have posted[0] it with subject, "[PATCH] taskstats: Unify cgroupstats.h with
    taskstats.h and use a single nla_policy". Please do review it.

    Thanks
    Nikanth

    [0] http://lkml.org/lkml/2009/7/13/189



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