On Sun, Jun 27 2010 at 5:49am -0400,
Christoph Hellwig <hch@xxxxxx> wrote:
> On Sat, Jun 26, 2010 at 04:31:24PM -0400, Mike Snitzer wrote:
> > Allow discards to be passed through to a single device linear mapping.
> > Introduce DM_TARGET_SUPPORTS_DISCARDS target features flag that each
> > target must set once discard support is added.
> >
> > Verify table's underlying devices support discards prior to setting the
> > associated DM device as capable of discards (via QUEUE_FLAG_DISCARD).
> >
> > Signed-off-by: Mike Snitzer <snitzer@xxxxxxxxxx>
> > ---
> > drivers/md/dm-linear.c | 1 +
> > drivers/md/dm-table.c | 51 ++++++++++++++++++++++++++++++++++
> > drivers/md/dm.c | 60 ++++++++++++++++++++++++++++++++--------
> > drivers/md/dm.h | 1 +
> > include/linux/device-mapper.h | 1 +
> > 5 files changed, 102 insertions(+), 12 deletions(-)
>
> > +static int device_discard_incapable(struct dm_target *ti, struct dm_dev *dev,
> > + sector_t start, sector_t len, void *data)
> > +{
> > + struct block_device *bdev = dev->bdev;
> > + struct request_queue *q = bdev_get_queue(bdev);
> > +
> > + WARN_ON(!q);
> > + return (!q || !blk_queue_discard(q));
> > +}
>
> How could a NULL queue happen here?
It really cannot, I was just being defensive.
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