From mboxrd@z Thu Jan 1 00:00:00 1970 From: Nadia Derbey Subject: Re: [RFC PATCH 0/5] Resend - Use procfs to change a syscall behavior Date: Thu, 10 Jul 2008 09:58:48 +0200 Message-ID: <4875C138.5060506@bull.net> References: <20080703144013.737951000@bull.net> <20080704102702.GB4531@elf.ucw.cz> <20080707190119.GB25934@us.ibm.com> <20080708105228.GB15311@elf.ucw.cz> <20080708215034.GB2179@us.ibm.com> <20080708215821.GE17083@elf.ucw.cz> <20080709022035.GA21249@us.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20080709022035.GA21249-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: containers-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org Errors-To: containers-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org To: "Serge E. Hallyn" Cc: containers-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org, Pavel Machek List-Id: containers.vger.kernel.org Serge E. Hallyn wrote: > Quoting Pavel Machek (pavel-+ZI9xUNit7I@public.gmane.org): > >>>>>>>An alternative to this solution consists in defining a new field in the >>>>>>>task structure (let's call it next_syscall_data) that, if set, would change >>>>>>>the behavior of next syscall to be called. The sys_fork_with_id() previously >>>>>>>cited can be replaced by >>>>>>> 1) set next_syscall_data to a target upid nr >>>>>>> 2) call fork(). >>>>>> >>>>>>...bloat task struct and >>>>>> >>>>>> >>>>>>>A new file is created in procfs: /proc/self/task//next_syscall_data. >>>>>>>This makes it possible to avoid races between several threads belonging to >>>>>>>the same process. >>>>>> >>>>>>...introducing this kind of uglyness. >>>>>> >>>>>>Actually, there were proposals for sys_indirect(), which is slightly >>>>>>less ugly, but IIRC we ended up with adding syscalls, too. >>>>> >>>>>Silly question... >>>>> >>>>>Oren, would you object to defining sys_fork_with_id(), >>>>>sys_msgget_with_id(), and sys_semget_with_id()? >>>>> >>>>>Eric, Pavel (Emelyanov), Dave, do you have preferences? >>>>> >>>>>For the cases Nadia has implemented here I'd be tempted to side with >>>>>Pavel Machek, but once we get to things like open() and socket(), (a) >>>>>the # new syscalls starts to jump, and (b) the per-syscall api starts to >>>>>seem a lot more cumbersome. >>>> >>>>You should not need to modify open/socket. You can already select fd >>>>by creatively using open/dup/close... >>> >>>That's what we do right now in cryo. And if we end up patching up every >>>API with separate syscalls, then we wouldn't create open_with_id(). But >>>so long as the next_id were to exist, exploiting it in open is nigh on >>>trivial and much nicer. >> >>Ok, so ignore previous email. You know how unix works. >> >>I believe you should just introduce syscalls you need. Yes, >>introducing new syscalls is hard/expensive, but changing existing >>syscalls is simply bad idea. > > > Ok, thanks, Pavel. I'm really far more inclined to agree with you than > it probably sounds like. I'll go ahead and implement a clone_with_id() > syscall for starters later this week just as a comparison. > > Unless, Nadia, you have already started that? Actually, what I've started working on these days is replace the proc interface by a syscall to set the next_syscall_data field: I think this might help us avoid defining a precise list of the new syscalls we need? Regards, Nadia > > >>So what new syscalls do you _really_ need? Not open_this_fd, nor >>socket_this_fd. > > > Oren, do you have a list of the syscalls which were modified to use the > next_id in zap? > > -serge > >