Re: [PATCH 2/2] block: create ioctl to discard-or-zeroout a range of blocks

Ric Wheeler
2016-03-11T04:42:34Z

On 03/11/2016 12:03 AM, Linus Torvalds wrote:
> On Thu, Mar 10, 2016 at 6:58 AM, Ric Wheeler <ricwheeler@gmail.com> wrote:
>> What was objectionable at the time this patch was raised years back (not
>> just to me, but to pretty much every fs developer at LSF/MM that year)
>> centered on the concern that this would be viewed as a "performance" mode
>> and we get pressure to support this for non-priveleged users. It gives any
>> user effectively the ability to read the block device content for previously
>> allocated data without restriction.
> The sane way to do it would be to just check permissions of the
> underlying block device.
>
> That way, people can just set the permissions for that to whatever
> they want. If google right now uses some magical group for this, they
> could make the underlying block device be writable for that group.
>
> We can do the security check at the filesystem level, because we have
> sb->s_bdev->bd_inode, and if you have read and write permissions to
> that inode, you might as well have permission to create a unsafe hole.
>
> That doesn't sound very hacky to me.
>
> Linus

I agree that this sounds quite reasonable.

Ric