From mboxrd@z Thu Jan 1 00:00:00 1970 From: Sukadev Bhattiprolu Subject: Re: [RFC][v8][PATCH 10/10]: Document clone3() syscall Date: Wed, 21 Oct 2009 11:27:15 -0700 Message-ID: <20091021182714.GA12955@us.ibm.com> References: <20091013044925.GA28181@us.ibm.com> <20091013045556.GJ28435@us.ibm.com> <20091019213636.GB1482@ucw.cz> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20091019213636.GB1482-+ZI9xUNit7I@public.gmane.org> Sender: linux-api-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Pavel Machek Cc: linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Oren Laadan , serue-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org, "Eric W. Biederman" , Alexey Dobriyan , Pavel Emelyanov , Andrew Morton , torvalds-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org, mikew-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org, mingo-X9Un+BFzKDI@public.gmane.org, hpa-YMNOUZJC4hwAvxtiuMwx3w@public.gmane.org, Nathan Lynch , arnd-r2nGTMty4D4@public.gmane.org, peterz-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org, Louis.Rilling-aw0BnHfMbSpBDgjK7y7TUQ@public.gmane.org, roland-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org, kosaki.motohiro-+CUm20s59erQFUHtdCDX3A@public.gmane.org, randy.dunlap-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org, linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Containers , sukadev-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org List-Id: linux-api@vger.kernel.org Pavel Machek [pavel-+ZI9xUNit7I@public.gmane.org] wrote: | Hi! | | > This gives a brief overview of the clone3() system call. We should | | Thanks! | | > eventually describe more details in existing clone(2) man page or in | > a new man page. | | M. Kerrisk (see MAINTAINERS) maintains man pages... Ok. I copied linux-api and M. Kerrisk is looking at this patchset. | | > Changelog[v8]: | > - clone2() is already in use in IA64. Rename syscall to clone3() | ... | > Index: linux-2.6/Documentation/clone2 | > =================================================================== | > --- /dev/null 1970-01-01 00:00:00.000000000 +0000 | > +++ linux-2.6/Documentation/clone2 2009-10-12 19:54:38.000000000 -0700 | | clone3? Ah, yes, will fix. | | > +struct clone_struct { | > + u64 flags; | > + u64 child_stack; | | u64 seems wrong on 32 bit platforms. ulong? | | > + u32 nr_pids; | | So nr_pids is either 1 or 2? No. With pid namespaces, which can be nested to arbitrary levels, each process has several pid numbers - one in its own namespace and one in each ancestor pid namespaces. nr_pids specifies the number of pids the user cares about. IOW, if you checkpoint a process that is 3 levels below the init-pid-ns, and you care about the pids for those three levels, you would pass in an array of 4 pid_ts and nr_pids would be 4. | | > + u32 reserved1; | > + u64 parent_tid; | > + u64 child_tid; | > + u64 reserved2; | > +}; | > + | | | > + See CLONE_NEWPID section of clone(2) man page for details about pid | > + namespaces. | > + | > + The order pids in @pids corresponds to the nesting order of pid- | > + namespaces, with @pids[0] corresponding to the init_pid_ns. | | Ok, so I'm confused. Hope the above note on pid-namespaces helps, if not let me know. | | > + If a pid in the @pids list is 0, the kernel will assign the next | > + available pid in the pid namespace, for the process. | > + | > + 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 with -EBUSY. | ... | > + On failure, clone3() returns -1 and sets 'errno' to one of following | > + values (the child process is not created). | | Inconsistent with above. Syscalls really return -ERRCODE, errno is | glibc magic. Ok. Will make it consistent to say that it returns one of the error codes.