linux-kernel - Re: [RFC] Per-thread getrusage

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Date:	Mon, 28 Jan 2008 10:48:23 +0300
From:	Pavel Emelyanov <xemul@...nvz.org>
To:	Andrew Morton <akpm@...ux-foundation.org>,
	Vinay Sridhar <vinay@...ux.vnet.ibm.com>
CC:	linux-kernel@...r.kernel.org, libc-alpha@...rceware.org,
	drepper@...hat.com, wli@...omorphy.com, sripathik@...ibm.com,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Pavel Emelyanov <xemul@...nvz.org>
Subject: Re: [RFC] Per-thread getrusage

Andrew Morton wrote:
> 	On Thu, 17 Jan 2008 13:57:05 +0530 Vinay Sridhar <vinay@...ux.vnet.ibm.com> wrote:
> 
>> Hi All,
>>
>> Last year, there was discussion about per-thread getrusage by adding
>> RUSAGE_THREAD flag to getrusage(). Please refer to the thread
>> http://lkml.org/lkml/2007/4/4/308. Ulrich had suggested that we should
>> design a better user-space API. Specifically, we need a
>> pthread_getrusage interface in the thread library, which accepts
>> pthread_t, converts pthread_t into the corresponding tid and passes it
>> down to the syscall.
>>
>> There are two ways to implement this in the kernel:
>> 1) Introduce an additional parameter 'tid' to sys_getrusage() and put
>> code in glibc to handle getrusage() and pthread_getrusage() calls
>> correctly.
>> 2) Introduce a new system call to handle pthread_getrusage() and leave
>> sys_getrusage() untouched.
>>
>> We implemented the second idea above, simply because it avoids touching
>> any existing code. We have implemented a new syscall, thread_getrusage()
>> and we have exposed pthread_getrusage() API to applications.
>>
>> Could you please share your thoughts on this? Does the approach look
>> alright? The code is hardly complete. It is just a prototype that works
>> on IA32 at the moment.
>>
>> ...
>>
>> +asmlinkage long sys_thread_getrusage(int tid, struct rusage __user *ru);
> 
> What happens if `tid' refers to a thread in a different pid namespace?
> 

That's impossible. I explicitly deny namespace creation in case the
CLONE_THREAD is specified. So all threads of a single process always
live in one pid namespace.

Thanks,
Pavel
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