On 08/09/09 9:19 -0400, Oren Laadan wrote: > > > Louis Rilling wrote: > > On 04/09/09 10:26 -0500, Serge E. Hallyn wrote: > >> Quoting Oren Laadan (orenl@xxxxxxxxxxx): > >>> During restart, we need to allocate pty slaves with the same > >>> identifiers as recorded during checkpoint. Modify the allocation code > >>> to allow an in-kernel caller to request a specific slave identifier. > >>> > >>> For this, add a new field to task_struct - 'required_id'. It will > >>> hold the desired identifier when restoring a (master) pty. > >>> > >>> The code in ptmx_open() will use this value only for tasks that try to > >>> open /dev/ptmx that are restarting (PF_RESTARTING), and if the value > >>> isn't CKPT_REQUIRED_NONE (-1). > >> So noone has indicated any preference for this versus the ptmx_create() > >> approach... > >> > >> I'm satisfied knowing we have a working fallback in case task->required_id > >> is deemed unacceptable. > >> > >> However I'd like to not have linux-kernel folks think us morons for not > >> having considered that. Can you add a message to the changelog saying > >> why we're going with this approach (namely, that it lets us re-use > >> filp_open() instead of having to do a custom alloc_file in a new code-path, > >> which introduces maintenance duplication for file permission checking > >> paths)? > > > > As far as I am concerned, I do have a preference for the ptmx_create() > > approach. This task->required_id field reminds me the former approach taken for > > restarting pids and (and SYSV IPC ids IIRC) from userspace, that was proposed > > last year and actually deemed unacceptable [ IIRC, this was an argument in favor > > of a restart() syscall ]. I know that it's not the same since ->required_id is > > not set from userspace and used in a later syscall, but still ... > > > > Moreover I see no reason whey there would be no way to refactorize ptmx code and > > have less duplicated code with the ptmx_create() approach. > > I basically agree - I simply took the easiest/fastest path; if the ptmx > code is properly refactored, we should use that instead. > > Did you have a chance to look at Serge's attempt to do exactly that ? > https://lists.linux-foundation.org/pipermail/containers/2009-September/020363.html I only had a quick look. Will try to look closer, but don't rely on me being quick at this. Thanks, Louis -- Dr Louis Rilling Kerlabs Skype: louis.rilling Batiment Germanium Phone: (+33|0) 6 80 89 08 23 80 avenue des Buttes de Coesmes http://www.kerlabs.com/ 35700 Rennes
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