On 10/31/2012 12:36 PM, Darrick J. Wong wrote:

On Wed, Oct 31, 2012 at 12:56:14PM +0100, Jan Kara wrote:

<snip>

quoted

You are right that we need a mechanism to push the flags from the devices
through various storage layers up into the bdi filesystem sees to make
things reliable.

md/dm will call blk_integrity_register, so pushing the "stable page writes
required" flag through the various layers is already taken care of.  If devices
and filesystems can both indicate that they want stable page writes,  I'll have
to keep track of however many users there are.

Please note again the iscsi case. Say the admin defined half of an md iscsi devices
with data_integrity and half without.

For me I would like an OR. If any underline device needs "stable pages" they all
get them.

Please also provide - or how easy is to make an API - for the like of iscsi that
given a request_queue, set the BDI's "stable pages" on. Something like:

/* stable_pages can only be turned on never off */
blk_set_stable_pages(struct request_queue); 

It does seem like less work to fix all the filesystems than to dork around with
another flag.

Sure if that is possible, that will be perfect, then I do not need to keep
the old "unstable pages" code around at all.

Thanks for working on this
Boaz