Messages in this thread | | | Date | Wed, 27 Jun 2001 04:31:55 -0400 (EDT) | From | Alexander Viro <> | Subject | Re: Maximum mountpoints + chrooted login |
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On Wed, 27 Jun 2001, Magnus Naeslund(f) wrote:
> I was thinking of doing a chrooted login for some ssh accounts. > The plan is this:
[snip CLONE_NAMESPACE-by-hands]
> Does this seem like a bad idea? > (then please tell me why :))
Mostly because there's a better way to do that. Yes, such scheme would work (that + massive pending fs/super.c cleanups was the main reason why I didn't go for proper solution in 2.4.0-test*). However, instead of crufting up kinda-sorta namespaces one could use the real thing. Relevant cleanups of superblock handling will go in in 2.5.very_early and the rest of patch (namespace proper) takes about 10Kb.
You can simply say clone(CLONE_NAMESPACE,NULL) and you get an independent set of mounts to play with. mount/umount whatever you want before dropping the root priveleges. All children of that process will share its namespace. When the last one goes away everything will be garbage-collected - no need to umount anything on logout.
> One problem could be the _massive_ mounts, 3*online_users. > Are there any limits/drawbacks doing it like this?
With the mntcache in - not really. It fixes the main performance problem. Memory cost is sizeof(struct vfsmount)*total amount of mountpoints. I.e. about 100 bytes per mountpoint. That's it.
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