Re: [PATCH 2/2] btrfs-progs: defrag: open files RO on new enough kernels or if root

From: Adam Borowski <kilobyte@angband.pl>
To: Nikolay Borisov <nborisov@suse.com>
Cc: David Sterba <dsterba@suse.cz>, linux-btrfs@vger.kernel.org
Subject: Re: [PATCH 2/2] btrfs-progs: defrag: open files RO on new enough kernels or if root
Date: Mon, 3 Sep 2018 13:28:48 +0200	[thread overview]
Message-ID: <20180903112848.dinguob7clx4m6g7@angband.pl> (raw)
In-Reply-To: <61784cbe-719b-a83f-8535-bb622c39edcb@suse.com>

On Mon, Sep 03, 2018 at 02:04:23PM +0300, Nikolay Borisov wrote:
> On  3.09.2018 13:14, Adam Borowski wrote:
> > -		fd = open(fpath, O_RDWR);
> > +		fd = open(fpath, defrag_ro);
> 
> Looking at the kernel code I think this is in fact incorrect, because in
> ioctl.c we have:
> 
>                 if (!(file->f_mode & FMODE_WRITE)) {
> 
>                         ret = -EINVAL;
> 
>                         goto out;
> 
>                 }
> 
> So it seems a hard requirement to have opened a file for RW when you
> want to defragment it.

Oif!  I confused this with dedup, which does allow root to dedup RO even on
old kernels.  Good catch.

-- 
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