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SubjectRe: [PATCH v7 1/2] fork: extend clone3() to support setting a PID
On 11/11, Adrian Reber wrote:
>
> v7:
> - changed set_tid to be an array to set the PID of a process
> in multiple nested PID namespaces at the same time as discussed
> at LPC 2019 (container MC)

cough... iirc you convinced me this is not needed when we discussed
the previous version ;) Nevermind, probably my memory fools me.

So far I only have some cosmetic nits,

> @@ -175,6 +187,18 @@ struct pid *alloc_pid(struct pid_namespace *ns)
>
> for (i = ns->level; i >= 0; i--) {
> int pid_min = 1;
> + int t_pos = 0;
^^^^^

I won't insist, but I'd suggest to cache set_tid[t_pos] instead to make
the code a bit more simple.

> @@ -186,12 +210,24 @@ struct pid *alloc_pid(struct pid_namespace *ns)
> if (idr_get_cursor(&tmp->idr) > RESERVED_PIDS)
> pid_min = RESERVED_PIDS;

You can probably move this code into the "else" branch below.

IOW, something like


for (i = ns->level; i >= 0; i--) {
int xxx = 0;

if (set_tid_size) {
int pos = ns->level - i;

xxx = set_tid[pos];
if (xxx < 1 || xxx >= pid_max)
return ERR_PTR(-EINVAL);
/* Also fail if a PID != 1 is requested and no PID 1 exists */
if (xxx != 1 && !tmp->child_reaper)
return ERR_PTR(-EINVAL);
if (!ns_capable(tmp->user_ns, CAP_SYS_ADMIN))
return ERR_PTR(-EPERM);
set_tid_size--;
}

idr_preload(GFP_KERNEL);
spin_lock_irq(&pidmap_lock);

if (xxx) {
nr = idr_alloc(&tmp->idr, NULL, xxx, xxx + 1,
GFP_ATOMIC);
/*
* If ENOSPC is returned it means that the PID is
* alreay in use. Return EEXIST in that case.
*/
if (nr == -ENOSPC)
nr = -EEXIST;
} else {
int pid_min = 1;
/*
* init really needs pid 1, but after reaching the
* maximum wrap back to RESERVED_PIDS
*/
if (idr_get_cursor(&tmp->idr) > RESERVED_PIDS)
pid_min = RESERVED_PIDS;
/*
* Store a null pointer so find_pid_ns does not find
* a partially initialized PID (see below).
*/
nr = idr_alloc_cyclic(&tmp->idr, NULL, pid_min,
pid_max, GFP_ATOMIC);
}

...

This way only the "if (set_tid_size)" block has to play with set_tid_size/set_tid.

note also that this way we can easily allow set_tid[some_level] == 0, we can
simply do

- if (xxx < 1 || xxx >= pid_max)
+ if (xxx < 0 || xxx >= pid_max)

although I don't think this is really useful.

Oleg.

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