[Devel] Re: [RFC][PATCH 4/4] PID: use the target ID specified in procfs
Pavel Emelyanov
xemul at openvz.org
Tue Mar 11 09:55:44 PDT 2008
Serge E. Hallyn wrote:
> Quoting Pavel Emelyanov (xemul at openvz.org):
>> Nadia Derbey wrote:
>>> Pavel Emelyanov wrote:
>>>> Nadia.Derbey at bull.net wrote:
>>>>
>>>>> @@ -122,14 +122,26 @@ static void free_pidmap(struct upid *upi
>>>>> atomic_inc(&map->nr_free);
>>>>> }
>>>>>
>>>>> -static int alloc_pidmap(struct pid_namespace *pid_ns)
>>>>> +static int alloc_pidmap(struct pid_namespace *pid_ns, struct pid_list *pid_l,
>>>>> + int level)
>>>>> {
>>>>> int i, offset, max_scan, pid, last = pid_ns->last_pid;
>>>>> struct pidmap *map;
>>>>>
>>>>> - pid = last + 1;
>>>>> - if (pid >= pid_max)
>>>>> - pid = RESERVED_PIDS;
>>>>> + if (!pid_l) {
>>>>> + pid = last + 1;
>>>>> + if (pid >= pid_max)
>>>>> + pid = RESERVED_PIDS;
>>>>> + } else {
>>>>> + /*
>>>>> + * There's a target pid, so use it instead
>>>>> + */
>>>>> + BUG_ON(level < 0);
>>>>> + pid = PID_AT(pid_l, level);
>>>>> + if (pid >= pid_max)
>>>>> + return -EINVAL;
>>>>> + }
>>>>> +
>>>>> offset = pid & BITS_PER_PAGE_MASK;
>>>>> map = &pid_ns->pidmap[pid/BITS_PER_PAGE];
>>>>> max_scan = (pid_max + BITS_PER_PAGE - 1)/BITS_PER_PAGE - !offset;
>>>>> @@ -153,9 +165,16 @@ static int alloc_pidmap(struct pid_names
>>>>> do {
>>>>> if (!test_and_set_bit(offset, map->page)) {
>>>>> atomic_dec(&map->nr_free);
>>>>> - pid_ns->last_pid = pid;
>>>>> + if (!pid_l)
>>>>> + pid_ns->last_pid = pid;
>>>>> + else
>>>>> + pid_ns->last_pid = max(last,
>>>>> + pid);
>>>>> return pid;
>>>>> }
>>>>> + if (pid_l)
>>>>> + /* Target pid is already in use */
>>>>> + return -EBUSY;
>>>>> offset = find_next_offset(map, offset);
>>>>> pid = mk_pid(pid_ns, map, offset);
>>>>> /*
>>>>> @@ -179,7 +198,7 @@ static int alloc_pidmap(struct pid_names
>>>>> }
>>>>> pid = mk_pid(pid_ns, map, offset);
>>>>> }
>>>>> - return -1;
>>>>> + return -ENOMEM;
>>>>> }
>>>>>
>>>>> int next_pidmap(struct pid_namespace *pid_ns, int last)
>>>> As fas as this particular piece of code is concerned this all can
>>>> be shrunk down to
>>>>
>>>> static int set_vpidmap(struct pid_namespace *ns, int pid)
>>>> {
>>>> int offset;
>>>> pidmap_t *map;
>>>>
>>>> offset = pid & BITS_PER_PAGE_MASK;
>>>> map = ns->pidmap + vpid / BITS_PER_PAGE;
>>>>
>>>> if (unlikely(alloc_pidmap_page(map)))
>>>> return -ENOMEM;
>>>>
>>>> if (test_and_set_bit(offset, map->page))
>>>> return -EEXIST;
>>>>
>>>> atomic_dec(&map->nr_free);
>>>> return pid;
>>>> }
>>>>
>>>> where the alloc_pidmap_page is a consolidated part of code from alloc_pidmap.
>>>>
>>>> And I'm scared of what the alloc_pid is going to become.
>>>>
>>>>
>>> It's true that I made alloc_pid() become uggly, but this patchset was
>>> more intended to continue a discussion.
>>>
>>> What we could do is the following (not compiled, not tested...):
>>>
>>> struct pid *alloc_pid(struct pid_namespace *ns)
>>> {
>>> struct pid *pid;
>>> enum pid_type type;
>>> int i, nr;
>>> struct pid_namespace *tmp;
>>> struct upid *upid;
>>>
>>> pid = kmem_cache_alloc(ns->pid_cachep, GFP_KERNEL);
>>> if (!pid) {
>>> pid = ERR_PTR(-ENOMEM);
>>> goto out;
>>> }
>>>
>>> tmp = ns;
>>> i = ns->level;
>>>
>>> if (current->next_id && (current->next_id->flag & SYS_ID_PID)) {
>>> tmp = set_predefined_pids(ns,
>>> current->next_id->pid_ids);
>>> if (IS_ERR(tmp)) {
>>> nr = PTR_ERR(tmp);
>>> goto out_free;
>>> }
>>> }
>>>
>>> /*
>>> * Let the lower levels upid nrs be automatically allocated
>>> */
>>> for ( ; i >= 0; i--) {
>>> nr = alloc_pidmap(tmp, NULL, -1);
>>> if (nr < 0)
>>> goto out_free;
>>> ....
>>>
>>> which would only add a test and a function call to alloc_pid() ==> more
>>> readable.
>>> with set_predefined_pids defined as follows (still not compiled, not
>>> tested, ...):
>>>
>>> struct pid_namespace *set_predefined_pids(struct pid_namespace *ns,
>>> struct pid_list *pid_l)
>>> {
>>> int rel_level;
>>>
>>> BUG_ON(!pid_l);
>>>
>>> rel_level = pid_l->npids - 1;
>>> if (rel_level > ns->level)
>>> return ERR_PTR(-EINVAL);
>>>
>>> /*
>>> * Use the predefined upid nrs for levels ns->level down to
>>> * ns->level - rel_level
>>> */
>>> for ( ; rel_level >= 0; i--, rel_level--) {
>>> nr = alloc_pidmap(tmp, pid_l, rel_level);
>>> if (nr < 0)
>>> return ERR_PTR(nr);
>>>
>>> pid->numbers[i].nr = nr;
>>> pid->numbers[i].ns = tmp;
>>> tmp = tmp->parent;
>>> }
>>>
>>> current->next_id->flag &= ~SYS_ID_PID;
>>> pids_free(pid_l);
>>> current->next_id->pid_ids = NULL;
>>>
>>> return tmp;
>>> }
>>>
>>>
>>> Don't you think that mixing this with your 1st proposal (the
>>> set_vpidmap() one), would make things look better?
>> I'd prefer seeing
>>
>> --- a/kernel/pid.c
>> +++ b/kernel/pid.c
>> @@ -247,7 +247,7 @@ struct pid *alloc_pid(struct pid_namespace *ns)
>> {
>> struct pid *pid;
>> enum pid_type type;
>> - int i, nr;
>> + int i, nr, req_nr;
>> struct pid_namespace *tmp;
>> struct upid *upid;
>>
>> @@ -257,7 +257,11 @@ struct pid *alloc_pid(struct pid_namespace *ns)
>>
>> tmp = ns;
>> for (i = ns->level; i >= 0; i--) {
>> - nr = alloc_pidmap(tmp);
>> + req_nr = get_required_pidnr(ns, i);
>> + if (req_nr > 0)
>> + nr = set_pidmap(tmp, req_nr);
>
> I assume you mean set_vpidmap(tmp, req_nr); here?
:) or however this one is called.
>> + else
>> + nr = alloc_pidmap(tmp);
>> if (nr < 0)
>> goto out_free;
>>
>>
>> in alloc_pid() and not much than that.
>
> So get_required_pidnr(ns, i) would do something like
>
> int get_required_pidnr(struct pid_namespace *ns, int i)
> {
> if (current->next_id && (current->next_id->flag & SYS_ID_PID)) {
> pid_l = current->next_id->pid_ids;
> if (!pid_l) return 0;
> rel_level = pid_l->npids - 1;
> if (rel_level <= i)
> return PID_AT(pid_l, i);
> }
> return 0;
> }
>
> ?
Well, yes, sort of. I haven't looked close to this part of patch,
but looks correct.
>>> Regards,
>>> Nadia
>>>
>> _______________________________________________
>> Containers mailing list
>> Containers at lists.linux-foundation.org
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>
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