Messages in this thread | | | Date | Fri, 6 Nov 2009 12:18:14 -0800 | From | Matt Helsley <> | Subject | Re: [v11][PATCH 9/9] Document clone_with_pids() syscall |
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On Fri, Nov 06, 2009 at 12:39:36PM -0600, Serge E. Hallyn wrote: > Quoting Sukadev Bhattiprolu (sukadev@us.ibm.com): > ... > > + If a pid in the @pids list is non-zero, the kernel tries to assign > > + the specified pid in that namespace. If that pid is already in use > > + by another process, the system call fails (see EBUSY below). > > + > > + The order of pids in @pids is oldest in pids[0] to youngest pid > > + namespace in pids[nr_pids-1]. If the number of pids specified in the > > In the sys_choosepid() discussion, Matt suggested it would be more > user-friendly to have the pid for the youngest pidns be pids[0]. > That way the user doesn't have to know their pidns depth.
As far as I could see, Suka's solution also does not require knowing the pidns depth (aka level). He made it so that copy_from_user() adjusts its destination using the discrepancy between the number of pids passed and the number of levels.
If userspace passes an array with n pids and there are k namespace levels then clone_with_pids() makes sure that the kernel sees a pid array like:
index 0 ... k - (n + 1) ... k - 1 +-----------------------+-------------------------+ pid_t | 0 ..................0 | <copied from userspace> | +-----------------------+-------------------------+
So even though the order is different from choosepid() the calling task still doesn't need to know its pidns level. Of course, just like choosepid(), n <= k or userspace will get EINVAL.
Cheers, -Matt Helsley
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