Quoting Pavel Emelianov (xemul@openvz.org):
> sukadev@us.ibm.com wrote:
> > Pavel Emelianov [xemul@openvz.org] wrote:
> > | sukadev@us.ibm.com wrote:
> > | > Subject: [PATCH 2/6] Rename pid_nr function 
> > | > 
> > | > From: Sukadev Bhattiprolu <sukadev@us.ibm.com>
> > | > 
> > | > Rename pid_nr() function to pid_to_nr() which is more descriptive
> > | > and will hopefully cause less confusion with new structure/functions
> > | > being added to support multiple pid namespaces.
> > | 
> > | Don't we need at least two convertors:
> > | pid_to_nr_as_it_seen_by_current()
> > | and
> > | pid_to_nr_as_it_seen_by_some_other_task()
> > 
> > Can you give me an example of where you would use this latter
> > (pid_to_nr_as_it_seen_by_some_other_task()) interface ?
> 
> Easy. Consider you're observing /proc/<pid>/status file for a task
> that lives in two namespaces - init and some created. When making 
> "cat" on this from init namespace you must get the task's pid as it
> is seen from init namespace, but when making "cat" from the created
> namespace you must see the pid as it is seen by this namespace. And 
> so on and so forth.

But 'current' in that case is the process reading the file, so you do in
fact want to use pid_to_nr_as_it_seen_by_current().

-serge

> On the other hand sys_getpid() should simply return the virtual pid
> without messing with namespaces.
> 
> > I have a similar confusion with following two sets of interfaces
> > in your patchset and have been meaning to discuss it further.
> > 
> > 	pid_nr() and pid_vnr()
> > 	find_pid() and find_vpid()
> > 
> > I can understand the use of pid_vnr() and find_vpid().
> > 
> > Where do you see us using pid_nr() and find_pid() - i.e the values
> > as seen in init_pid_ns ? 
> 
> find_pid() may be used in keventd_create_thread() as eventd thread
> lives in init namespace only. Any other place in kernel that is
> somehow "global" to all the namespaces and has no user interface
> must use global pids not to confuse the kernel.
> 
> Of course, if we plan to replace the notion of global numerical pid
> with struct pid this is not an option. However, the issues with the
> pid_to_nr_as_it_... are still valid.
> 
> > Like I pointed out in another thread, sunos_killpg() for instance
> > needs to used find_vpid(). Similarly, kill_proc_info(),
> > __set_special_pids() etc need find_vpid().
> 
> Sure. These places are to be patched as well.
> 
> > Thanks,
> > 
> > Suka
> > 
> > 
> > | 
> > | The first one is essentially the second one with "some other
> > | task" being current, but it can be optimized...
> > | 
> > | > Signed-off-by: Sukadev Bhattiprolu <sukadev@us.ibm.com>
> > | > ---
> > | >  drivers/char/n_r3964.c |    7 ++++---
> > | >  drivers/char/tty_io.c  |    4 ++--
> > | >  fs/autofs/root.c       |    2 +-
> > | >  fs/fcntl.c             |    2 +-
> > | >  fs/proc/array.c        |    2 +-
> > | >  fs/smbfs/proc.c        |    2 +-
> > | >  include/linux/pid.h    |    2 +-
> > | >  ipc/mqueue.c           |    2 +-
> > | >  kernel/container.c     |    2 +-
> > | >  kernel/fork.c          |    2 +-
> > | >  kernel/sysctl.c        |    2 +-
> > | >  11 files changed, 15 insertions(+), 14 deletions(-)
> > | > 
> > | > Index: lx26-22-rc6-mm1/include/linux/pid.h
> > | > ===================================================================
> > | > --- lx26-22-rc6-mm1.orig/include/linux/pid.h	2007-07-05 18:53:43.000000000 -0700
> > | > +++ lx26-22-rc6-mm1/include/linux/pid.h	2007-07-05 18:54:29.000000000 -0700
> > | > @@ -98,7 +98,7 @@ extern struct pid *find_ge_pid(int nr);
> > | >  extern struct pid *alloc_pid(void);
> > | >  extern void FASTCALL(free_pid(struct pid *pid));
> > | >  
> > | > -static inline pid_t pid_nr(struct pid *pid)
> > | > +static inline pid_t pid_to_nr(struct pid *pid)
> > | >  {
> > | >  	pid_t nr = 0;
> > | >  	if (pid)
> > | > Index: lx26-22-rc6-mm1/drivers/char/n_r3964.c
> > | > ===================================================================
> > | > --- lx26-22-rc6-mm1.orig/drivers/char/n_r3964.c	2007-07-05 18:53:43.000000000 -0700
> > | > +++ lx26-22-rc6-mm1/drivers/char/n_r3964.c	2007-07-05 18:54:29.000000000 -0700
> > | > @@ -771,7 +771,7 @@ static int enable_signals(struct r3964_i
> > | >  
> > | >  			if (pClient->pid == pid) {
> > | >  				TRACE_PS("removing client %d from client list",
> > | > -					 pid_nr(pid));
> > | > +					 pid_to_nr(pid));
> > | >  				*ppClient = pClient->next;
> > | >  				while (pClient->msg_count) {
> > | >  					pMsg = remove_msg(pInfo, pClient);
> > | > @@ -801,7 +801,8 @@ static int enable_signals(struct r3964_i
> > | >  			if (pClient == NULL)
> > | >  				return -ENOMEM;
> > | >  
> > | > -			TRACE_PS("add client %d to client list", pid_nr(pid));
> > | > +			TRACE_PS("add client %d to client list",
> > | > +					pid_to_nr(pid));
> > | >  			spin_lock_init(&pClient->lock);
> > | >  			pClient->sig_flags = arg;
> > | >  			pClient->pid = get_pid(pid);
> > | > @@ -933,7 +934,7 @@ static void remove_client_block(struct r
> > | >  {
> > | >  	struct r3964_block_header *block;
> > | >  
> > | > -	TRACE_PS("remove_client_block PID %d", pid_nr(pClient->pid));
> > | > +	TRACE_PS("remove_client_block PID %d", pid_to_nr(pClient->pid));
> > | >  
> > | >  	block = pClient->next_block_to_read;
> > | >  	if (block) {
> > | > Index: lx26-22-rc6-mm1/drivers/char/tty_io.c
> > | > ===================================================================
> > | > --- lx26-22-rc6-mm1.orig/drivers/char/tty_io.c	2007-07-05 18:53:43.000000000 -0700
> > | > +++ lx26-22-rc6-mm1/drivers/char/tty_io.c	2007-07-05 18:54:29.000000000 -0700
> > | > @@ -3080,7 +3080,7 @@ static int tiocgpgrp(struct tty_struct *
> > | >  	 */
> > | >  	if (tty == real_tty && current->signal->tty != real_tty)
> > | >  		return -ENOTTY;
> > | > -	return put_user(pid_nr(real_tty->pgrp), p);
> > | > +	return put_user(pid_to_nr(real_tty->pgrp), p);
> > | >  }
> > | >  
> > | >  /**
> > | > @@ -3151,7 +3151,7 @@ static int tiocgsid(struct tty_struct *t
> > | >  		return -ENOTTY;
> > | >  	if (!real_tty->session)
> > | >  		return -ENOTTY;
> > | > -	return put_user(pid_nr(real_tty->session), p);
> > | > +	return put_user(pid_to_nr(real_tty->session), p);
> > | >  }
> > | >  
> > | >  /**
> > | > Index: lx26-22-rc6-mm1/fs/autofs/root.c
> > | > ===================================================================
> > | > --- lx26-22-rc6-mm1.orig/fs/autofs/root.c	2007-07-05 18:53:43.000000000 -0700
> > | > +++ lx26-22-rc6-mm1/fs/autofs/root.c	2007-07-05 18:54:29.000000000 -0700
> > | > @@ -214,7 +214,7 @@ static struct dentry *autofs_root_lookup
> > | >  
> > | >  	oz_mode = autofs_oz_mode(sbi);
> > | >  	DPRINTK(("autofs_lookup: pid = %u, pgrp = %u, catatonic = %d, "
> > | > -				"oz_mode = %d\n", pid_nr(task_pid(current)),
> > | > +				"oz_mode = %d\n", pid_to_nr(task_pid(current)),
> > | >  				process_group(current), sbi->catatonic,
> > | >  				oz_mode));
> > | >  
> > | > Index: lx26-22-rc6-mm1/fs/fcntl.c
> > | > ===================================================================
> > | > --- lx26-22-rc6-mm1.orig/fs/fcntl.c	2007-07-05 18:53:43.000000000 -0700
> > | > +++ lx26-22-rc6-mm1/fs/fcntl.c	2007-07-05 18:54:29.000000000 -0700
> > | > @@ -305,7 +305,7 @@ pid_t f_getown(struct file *filp)
> > | >  {
> > | >  	pid_t pid;
> > | >  	read_lock(&filp->f_owner.lock);
> > | > -	pid = pid_nr(filp->f_owner.pid);
> > | > +	pid = pid_to_nr(filp->f_owner.pid);
> > | >  	if (filp->f_owner.pid_type == PIDTYPE_PGID)
> > | >  		pid = -pid;
> > | >  	read_unlock(&filp->f_owner.lock);
> > | > Index: lx26-22-rc6-mm1/fs/proc/array.c
> > | > ===================================================================
> > | > --- lx26-22-rc6-mm1.orig/fs/proc/array.c	2007-07-05 18:53:43.000000000 -0700
> > | > +++ lx26-22-rc6-mm1/fs/proc/array.c	2007-07-05 18:54:29.000000000 -0700
> > | > @@ -398,7 +398,7 @@ static int do_task_stat(struct task_stru
> > | >  		struct signal_struct *sig = task->signal;
> > | >  
> > | >  		if (sig->tty) {
> > | > -			tty_pgrp = pid_nr(sig->tty->pgrp);
> > | > +			tty_pgrp = pid_to_nr(sig->tty->pgrp);
> > | >  			tty_nr = new_encode_dev(tty_devnum(sig->tty));
> > | >  		}
> > | >  
> > | > Index: lx26-22-rc6-mm1/fs/smbfs/proc.c
> > | > ===================================================================
> > | >