From mboxrd@z Thu Jan  1 00:00:00 1970
From: ebiederm@xmission.com (Eric W. Biederman)
Date: Tue, 08 May 2018 20:23:19 -0500
Subject: [PATCH 2/4] pid: Export find_task_by_vpid for use in external
 modules
In-Reply-To: <20180508140640.0e312dba025df75cbf205cdb@arm.com> (Kim Phillips's
 message of "Tue, 8 May 2018 14:06:40 -0500")
References: <20180508140640.0e312dba025df75cbf205cdb@arm.com>
Message-ID: <87k1sdvczc.fsf@xmission.com>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

Kim Phillips <kim.phillips@arm.com> writes:

> This patch is in the context of allowing the Coresight h/w
> trace driver suite to be loaded as modules.  Coresight uses
> find_task_by_vpid when running in direct capture mode (via sysfs)
> when getting/setting the context ID comparator to trigger on
> (/sys/bus/coresight/devices/<x>.etm/ctxid_pid).

Nacked-by: "Eric W. Biederman" <ebiederm@xmission.com>

There is no way to implement a sysfs file that takes a pid correctly.
Don't do it.

Pids are tied to pid namespaces and sysfs deliberately does not do
anything remotely resembly a pid namespace.

Eric


> Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Oleg Nesterov <oleg@redhat.com>
> Cc: Gargi Sharma <gs051095@gmail.com>
> Cc: Rik van Riel <riel@redhat.com>
> Cc: Pavel Tatashin <pasha.tatashin@oracle.com>
> Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
> Cc: Kirill Tkhai <ktkhai@virtuozzo.com>
> Cc: Mike Rapoport <rppt@linux.vnet.ibm.com>
> Cc: David Howells <dhowells@redhat.com>
> Cc: "Eric W. Biederman" <ebiederm@xmission.com>
> Signed-off-by: Kim Phillips <kim.phillips@arm.com>
> ---
> Current CoreSight callsite:
>
> https://lxr.missinglinkelectronics.com/linux/include/linux/coresight.h#L285
>
> A quick look didn't find anything, but if Coresight needs to do
> something differently, please comment.
>
>  kernel/pid.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/kernel/pid.c b/kernel/pid.c
> index 157fe4b19971..92b1b623f3e0 100644
> --- a/kernel/pid.c
> +++ b/kernel/pid.c
> @@ -342,6 +342,7 @@ struct task_struct *find_task_by_vpid(pid_t vnr)
>  {
>  	return find_task_by_pid_ns(vnr, task_active_pid_ns(current));
>  }
> +EXPORT_SYMBOL_GPL(find_task_by_vpid);
>  
>  struct task_struct *find_get_task_by_vpid(pid_t nr)
>  {