Messages in this thread | | | From | (Eric W. Biederman) | Subject | Re: [Containers] [PATCH 5/7] pid: Implement pid_nr | Date | Wed, 16 Aug 2006 00:29:18 -0600 |
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Dave Hansen <haveblue@us.ibm.com> writes:
> On Tue, 2006-08-15 at 13:00 -0600, Eric W. Biederman wrote: >> Dave Hansen <haveblue@us.ibm.com> writes: >> >> > On Tue, 2006-08-15 at 12:23 -0600, Eric W. Biederman wrote: >> >> +static inline pid_t pid_nr(struct pid *pid) >> >> +{ >> >> + pid_t nr = 0; >> >> + if (pid) >> >> + nr = pid->nr; >> >> + return nr; >> >> +} >> > >> > When is it valid to be passing around a NULL 'struct pid *'? >> >> When you don't have one at all. Look at the fcntl case a few >> patches later, or even the spawnpid case. > > Does the fcntl() one originate from anywhere other than find_pid() in > f_setown()? It seems like, perhaps, the error checking is being done at > the wrong level.
Yes. It is normally NULL as file handles don't usually have a process to send a signal to.
>> Then of course there is the later chaos when we get to pid spaces >> where depending on the pid namespace you are in when you call this >> on a given struct pid sometimes you will get a pid value and sometimes >> you won't. > > OK, I think it is makes sense to me to say 'get_pid(tsk, pidspace)' and > get back a NULL 'struct pid' if that task isn't visible in that > namespace. However, I don't get how it is handy to be able to defer the > fact that the pid wasn't found until you go do a pid_nr() on that NULL.
If having a pid to signal is optional, which it almost always is, being able to handle that case easily and return a 0 to user space is helpful.
So far it is my assumption that everything that looks up a pid and converts a pid to a number will do it with respect to the current processes pidspace. A very reasonable assumption and only with siginfo have I found a case where it looks like I might not be able to implement it that way.
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