[Devel] Re: [RFC][PATCH] Pid namespaces vs locks interaction

[Vitaliy Gusev]

Hello

On 6 December 2007 18:51:30 Serge E. Hallyn wrote:
> > fl_pid is used by nfs, fuse and gfs2. For instance nfs  keeps in fl_pid
> > some unique id to identify locking process between hosts - it is not a
> > process pid.
>
> Ok, but so the struct user_flock->fl_pid is being set to the task's
> virtual pid, while the struct kernel_flock->fl_pid is being set to
> task->tgid for nfsd use.
>
> Why can't nfs just generate a uniqueid from the struct pid when it
> needs it?

I think it is hard. lockd uses struct nlm_host to get process unique id (see 
__nlm_alloc_pid() function).

>
> Fuse just seems to copy the pid to report it to userspace, so it would
> just copy pid_vnr(kernel_flock->pid) into user_flock->fl_pid.
>
> Anyway I haven't looked at all the uses of struct fl_pid, but you
> can always get the pidnr back from the struct pid if needed so there
> should be no problem.
>
> The split definately seems worthwhile to me, so that
> user_flock->fl_pidnr can always be said to be the pid in the acting
> process' namespace, and flock->fl_pid can always be a struct pid,
> rather than having fl_pid sometimes be current->tgid, or sometimes
> pid_vnr(flock->fl_nspid)...
>
> -serge
> -
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-- 
Thank,
Vitaliy Gusev
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