linux-kernel - Re: [RFC v6 02/40] vfs: Add MAY_CREATE_FILE and MAY_CREATE

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Date:	Wed, 2 Sep 2015 15:20:08 -0400
From:	"J. Bruce Fields" <bfields@...ldses.org>
To:	Andreas Gruenbacher <agruenba@...hat.com>
Cc:	Andreas Gruenbacher <andreas.gruenbacher@...il.com>,
	linux-kernel@...r.kernel.org,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	linux-nfs@...r.kernel.org, linux-api@...r.kernel.org,
	linux-cifs@...r.kernel.org, linux-security-module@...r.kernel.org
Subject: Re: [RFC v6 02/40] vfs: Add MAY_CREATE_FILE and MAY_CREATE_DIR
 permission flags

On Wed, Sep 02, 2015 at 09:06:32PM +0200, Andreas Gruenbacher wrote:
> 2015-09-02 20:53 GMT+02:00 J. Bruce Fields <bfields@...ldses.org>:
> >> @@ -453,7 +453,8 @@ static int sb_permission(struct super_block *sb, struct inode *inode, int mask)
> >>   * this, letting us set arbitrary permissions for filesystem access without
> >>   * changing the "normal" UIDs which are used for other things.
> >>   *
> >> - * When checking for MAY_APPEND, MAY_WRITE must also be set in @mask.
> >> + * When checking for MAY_APPEND, MAY_CREATE_FILE, MAY_CREATE_DIR,
> >> + * MAY_WRITE must also be set in @mask.
> >
> > Why?
> 
> So that file systems that don't support MAY_APPEND can ignore the flag
> and will then automatically check for MAY_WRITE instead.

Got it.  And maybe it should be obvious, but it might be worth a
sentence in the changelog if it's not already explained elsewhere.--b.

> 
> > (Also: written as a simple list like that, it's a ambiguous how to
> > parse that comment: I think you mean that MAY_WRITE must be set whenever
> > MAY_APPEND, MAY_CREATE_FILE, or MAY_CREATE_DIR are set.)
> 
> Yes, that's better.
> 
> Thanks,
> Andreas
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