linux-kernel - Re: [patch 5/9] unprivileged mounts: allow unprivileged bind mounts

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Date:	Wed, 9 Jan 2008 13:45:09 +0100 (CET)
From:	Jan Engelhardt <jengelh@...putergmbh.de>
To:	Miklos Szeredi <miklos@...redi.hu>
cc:	haveblue@...ibm.com, akpm@...ux-foundation.org, hch@...radead.org,
	serue@...ibm.com, viro@....linux.org.uk, ebiederm@...ssion.com,
	kzak@...hat.com, linux-fsdevel@...r.kernel.org,
	containers@...ts.osdl.org, util-linux-ng@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [patch 5/9] unprivileged mounts: allow unprivileged bind mounts


On Jan 8 2008 20:08, Miklos Szeredi wrote:
>> On Tue, 2008-01-08 at 12:35 +0100, Miklos Szeredi wrote:
>> > +static int reserve_user_mount(void)
>> > +{
>> > +       int err = 0;
>> > +
>> > +       spin_lock(&vfsmount_lock);
>> > +       if (nr_user_mounts >= max_user_mounts && !capable(CAP_SYS_ADMIN))
>> > +               err = -EPERM;
>> > +       else
>> > +               nr_user_mounts++;
>> > +       spin_unlock(&vfsmount_lock);
>> > +       return err;
>> > +} 
>> 
>> Would -ENOSPC or -ENOMEM be a more descriptive error here?  
>
>The logic behind EPERM, is that this failure is only for unprivileged
>callers.  ENOMEM is too specifically about OOM.  It could be changed
>to ENOSPC, ENFILE, EMFILE, or it could remain EPERM.  What do others
>think?

ENOSPC: No space remaining on device => 'wth'.
ENOMEM: I usually think of a userspace OOM (e.g. malloc'ed out all of your
32-bit address space on 32-bit processes)
EMFILE: "Too many open files"
ENFILE: "Too many open files in system".

ENFILE seems like a temporary winner among these four.

Back in the old days, when the number of mounts was limited in Linux,
what error value did it return? That one could be used.
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