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

[Vitaliy Gusev]

On 12 December 2007 20:31:15 Serge E. Hallyn wrote:
> Quoting Vitaliy Gusev (vgusev at openvz.org):
> > 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).
>
> Looks pretty simple though...  That whole set of code could even stay
> the same except for in __nlm_alloc_pid():
>
> 	option 1: compare struct pid* instead of uint32_t pid
> 	option 2: use the "global pid" out of the stored struct pid,
> 		something like pid->numbers[0].nr.

We can't use process pid. Process pid is circulated!  NFS (lockd)  needs 
unique process id between hosts which can't repeat oneself.

>
> > > 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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-- 
Thank,
Vitaliy Gusev
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