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

From: Theodore Ts'o
Date: Mon Mar 14 2016 - 10:46:32 EST

On Mon, Mar 14, 2016 at 06:34:00AM -0400, Ric Wheeler wrote:
> I think that once we enter this mode, the local file system has effectively
> ceded its role to prevent stale data exposure to the upper layer. In effect,
> this ceases to become a normal file system for any enabled process if we
> control this through fallocate() or for all processes if we do the brute
> force mount option that would be file system wide.

Or we do this via group id, such that we are ceding responsibility for
proventing stale data exposure to the processes running under that
group id. That process has the responsibility for making sure that it
doesn't return any data from that file unless it has been written, and
also to make sure the permissions of that file are not readable by
processes that aren't in that group. (For example, owned by user
ceph, group ceph, with premissions 640).

> In the end, that is the actual goal - move this enforcement up a layer for
> overlay/user space file systems that are then responsible for policing this
> ind of thing.

Yes, exactly.

- Ted