Messages in this thread | | | From | (Eric W. Biederman) | Date | Fri, 07 Nov 2008 07:51:32 -0800 | Subject | Re: [PATCH 2/7] proc: Implement support for automounts in task directories |
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Andrew Morton <akpm@linux-foundation.org> writes:
> On Thu, 06 Nov 2008 19:51:23 -0800 ebiederm@xmission.com (Eric W. Biederman) > wrote: > >> If we could do all of this with reference counting so that the >> mount would persist exactly until the last user of it has gone >> away without a periodic poll I would love it. But the infrastructure >> doesn't support that today, > > Well that sucks. The free-on-last-put idiom occurs in so many places > and serves us so well. I wonder what went wrong here?
> I guess it has interactions with dentry and inode cache aging which > could get tricky.
At least in part. If you just have the dentry you can't easily find what is mounted on it.
>> and where this is at least partially >> a bug fix I would rather not have the change depend on enhancing >> the VFS. >> >> The algorithm is actually very aggressive and in practice you don't >> see any /proc/<pid>/net showing up as a mount point. > > Do you think it has failure modes? Most particularly: obscure usage > patterns which can cause memory exhaustion?
I don't think we can pin anything that way that we can't pin right now.
You might be able to pin more if you happen to mount something on top of /proc/<pid>/net/ but that is an unprivileged operation.
>> > Obviously, that becomes clearer as one spends more time with the code, >> > but I wonder whether this has all been made as maintainble as it >> > possibly could be. >> >> Good question. >> >> In the sense of will we have to go through and futz with the code all >> of the time. The abstraction seems good. You put a mount on >> the proc_automounts list with do_add_mounts and it goes away eventually >> with all of the vfs rules maintained. >> >> In the sense of can the code be read? Perhaps it could be better. >> I expect it helps to have run the code and see /proc/net as a filesystem. >> that is magically mounted. > > 'twould be a useful contribution if you were to enshrine your > discoveries in /*these things*/. You knew I was working up to that :)
Short of a big fat comment I'm not certain if there is something I can do better.
Eric
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