Messages in this thread |  | | | Date | Mon, 07 Nov 2011 14:15:07 -0800 | | From | KOSAKI Motohiro <> | | Subject | Re: [RFC PATCH] tmpfs: support user quotas |
| |
(11/7/2011 6:30 AM), Lennart Poettering wrote: > On Mon, 07.11.11 13:58, Alan Cox (alan@lxorguk.ukuu.org.uk) wrote: > >> >>> Right, rlimit approach guarantees a simple way of dealing with users >>> across all tmpfs instances. >> >> Which is almost certainly not what you want to happen. Think about direct >> rendering. > > I don't see what direct rendering has to do with closing the security > hole that /dev/shm currently is. > >> For simple stuff tmpfs already supports size/nr_blocks/nr_inodes mount >> options so you can mount private resource constrained tmpfs objects >> already without kernel changes. No rlimit hacks needed - and rlimit is >> the wrong API anyway. > > Uh? I am pretty sure we don't want to mount a private tmpfs for each > user in /dev/shm and /tmp. If you have 500 users you'd have 500 tmpfs on > /tmp and on /dev/shm. Despite that without some ugly namespace hackery > you couldn't make them all appear in /tmp as /dev/shm without > subdirectories. Don't forget that /dev/shm and /tmp are an established > userspace API. > > Resource limits are exactly the API that makes sense here, because: > > a) we only want one tmpfs on /tmp, and one tmpfs on /dev/shm, not 500 on > each for each user
Ok, seems fair.
> b) we cannot move /dev/shm, /tmp around without breaking userspace > massively
agreed.
> > c) we want a global limit across all tmpfs file systems for each user
Why? Is there any benefit this?
> d) we don't want to have to upload the quota database into each tmpfs at > mount time. > > And hence: a per user RLIMIT is exactly the minimal solution we want > here.
If you want per-user limitation, RLIMIT is bad idea. RLIMIT is only inherited by fork. So, The api semantics clearly mismatch your usecase.
Instead, I suggest to implement new sysfs knob.
Thank you.
|  |