[Devel] Re: [PATCH 8/15] Helpers to find the task by its numerical ids

[Pavel Emelyanov]

Dave Hansen wrote:
> On Thu, 2007-07-26 at 18:51 +0400, Pavel Emelyanov wrote:
>> +extern struct task_struct *find_task_by_pid_type_ns(int type, int pid,
>> +		struct pid_namespace *ns);
>> +
>> +#define find_task_by_pid_ns(nr, ns)	\
>> +		find_task_by_pid_type_ns(PIDTYPE_PID, nr, ns)
>> +#define find_task_by_pid_type(type, nr)	\
>> +		find_task_by_pid_type_ns(type, nr, &init_pid_ns)
>> +#define find_task_by_pid(nr)		\
>> +		find_task_by_pid_type(PIDTYPE_PID, nr)
>> +
>>  extern void __set_special_pids(pid_t session, pid_t pgrp);
> 
> Do these _have_ to be macros?

No, but why not?
I can make them static inline functions, but why are macros that bad?

>>  /* per-UID process charging. */
>> diff -upr linux-2.6.23-rc1-mm1.orig/kernel/pid.c linux-2.6.23-rc1-mm1-7/kernel/pid.c
>> --- linux-2.6.23-rc1-mm1.orig/kernel/pid.c	2007-07-26 16:34:45.000000000 +0400
>> +++ linux-2.6.23-rc1-mm1-7/kernel/pid.c	2007-07-26 16:36:37.000000000 +0400
>> @@ -204,19 +221,20 @@ static void delayed_put_pid(struct rcu_h
>>  	goto out;
>>  }
>>
>> -struct pid * fastcall find_pid(int nr)
>> +struct pid * fastcall find_pid_ns(int nr, struct pid_namespace *ns)
>>  {
>>  	struct hlist_node *elem;
>> -	struct pid *pid;
>> +	struct upid *pnr;
>> +
>> +	hlist_for_each_entry_rcu(pnr, elem,
>> +			&pid_hash[pid_hashfn(nr, ns)], pid_chain)
>> +		if (pnr->nr == nr && pnr->ns == ns)
>> +			return container_of(pnr, struct pid,
>> +					numbers[ns->level]);
> 
> Do we do this loop anywhere else?  Should we have a for_each_pid() that
> makes this a little less messy?

No. Iteration over the hash chain happens here only.

>> -	hlist_for_each_entry_rcu(pid, elem,
>> -			&pid_hash[pid_hashfn(nr)], pid_chain) {
>> -		if (pid->nr == nr)
>> -			return pid;
>> -	}
>>  	return NULL;
>>  }
>> -EXPORT_SYMBOL_GPL(find_pid);
>> +EXPORT_SYMBOL_GPL(find_pid_ns);
>>
>>  /*
>>   * attach_pid() must be called with the tasklist_lock write-held.
>> @@ -318,12 +355,13 @@ struct task_struct * fastcall pid_task(s
>>  /*
>>   * Must be called under rcu_read_lock() or with tasklist_lock read-held.
>>   */
>> -struct task_struct *find_task_by_pid_type(int type, int nr)
>> +struct task_struct *find_task_by_pid_type_ns(int type, int nr,
>> +		struct pid_namespace *ns)
>>  {
>> -	return pid_task(find_pid(nr), type);
>> +	return pid_task(find_pid_ns(nr, ns), type);
>>  }
>>
>> -EXPORT_SYMBOL(find_task_by_pid_type);
>> +EXPORT_SYMBOL(find_task_by_pid_type_ns);
>>
>>  struct pid *get_task_pid(struct task_struct *task, enum pid_type type)
>>  {
>> @@ -342,7 +426,7 @@ struct pid *find_get_pid(pid_t nr)
>>  	struct pid *pid;
>>
>>  	rcu_read_lock();
>> -	pid = get_pid(find_pid(nr));
>> +	pid = get_pid(find_vpid(nr));
>>  	rcu_read_unlock();
> 
> OK, I think this is really confusing.  If find_get_pid() finds vpids,
> should we not call it find_get_vpid()?

I'd better make it find_get_pid_ns() with two arguments and made a couple
of macros (or static inlines) for global search and local search.

> -- Dave
> 
> 

Thanks,
Pavel