linux-kernel - Re: [patch 03/15] cgroup: dont call vfs

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Date:	Mon, 05 May 2008 14:32:22 +0200
From:	Miklos Szeredi <miklos@...redi.hu>
To:	hch@...radead.org
CC:	miklos@...redi.hu, akpm@...ux-foundation.org, hch@...radead.org,
	viro@...IV.linux.org.uk, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, menage@...gle.com
Subject: Re: [patch 03/15] cgroup: dont call vfs_mkdir

> > From: Miklos Szeredi <mszeredi@...e.cz>
> > 
> > cgroup_clone() calls vfs_mkdir() to create a directory in the cgroup
> > filesystem.  Replace with explicit call to cgroup_mkdir() and
> > fsnotify_mkdir().
> > 
> > This is equivalent, except that the following functions are not called
> > before cgroup_mkdir():
> > 
> >  - may_create()
> >  - security_inode_mkdir()
> >  - DQUOT_INIT()
> > 
> > Permission to clone the cgroup has already been checked in
> > copy_namespaces() (requiring CAP_SYS_ADMIN).  Additional file system
> > related capability checks are inappropriate and confusing.
> > 
> > The quota check is unnecessary, as quotas don't make any sense for
> > this filesystem.
> 
> Looks correct but I don't think it's a good idea.  Spreading more logic
> into filesystems without a good reason is rarely a good idea.

(Thanks for the review, Christoph)

Agreed completely, but vfs_* aren't for filesystems to call, rather
for entities calling _into_ filesystems from the outside.  This is
actually a very rare thing, so adding some extra logic for the sake of
cleanliness should be OK.

Now it can be argued, that cgroup_clone() is calling into the
filesystem from the outside.  But it's not really doing that, rather
it's making an internal modification to a specific filesystem,
triggered by some external action.

Miklos
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