On Wed, Mar 03 2021 at 6:57am -0500,
Jeffle Xu <jefflexu@xxxxxxxxxxxxxxxxx> wrote:
> This method can be used to check if bio-based device supports IO polling
> or not. For mq devices, checking for hw queue in polling mode is
> adequate, while the sanity check shall be implementation specific for
> bio-based devices. For example, dm device needs to check if all
> underlying devices are capable of IO polling.
>
> Though bio-based device may have done the sanity check during the
> device initialization phase, cacheing the result of this sanity check
> (such as by cacheing in the queue_flags) may not work. Because for dm
s/cacheing/caching/
> devices, users could change the state of the underlying devices through
> '/sys/block/<dev>/io_poll', bypassing the dm device above. In this case,
> the cached result of the very beginning sanity check could be
> out-of-date. Thus the sanity check needs to be done every time 'io_poll'
> is to be modified.
>
> Signed-off-by: Jeffle Xu <jefflexu@xxxxxxxxxxxxxxxxx>
Ideally QUEUE_FLAG_POLL would be authoritative.. but I appreciate the
problem you've described. Though I do wonder if this should be solved
by bio-based's fops->poll() method clearing the request_queue's
QUEUE_FLAG_POLL if it finds an underlying device doesn't have
QUEUE_FLAG_POLL set. Though making bio-based's fops->poll() always need
to validate the an underlying device does support polling is pretty
unfortunate.
Either way, queue_poll_store() will need to avoid blk-mq specific poll
checking for bio-based devices.
Mike
> ---
> block/blk-sysfs.c | 14 +++++++++++---
> include/linux/blkdev.h | 1 +
> 2 files changed, 12 insertions(+), 3 deletions(-)
>
> diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
> index 0f4f0c8a7825..367c1d9a55c6 100644
> --- a/block/blk-sysfs.c
> +++ b/block/blk-sysfs.c
> @@ -426,9 +426,17 @@ static ssize_t queue_poll_store(struct request_queue *q, const char *page,
> unsigned long poll_on;
> ssize_t ret;
>
> - if (!q->tag_set || q->tag_set->nr_maps <= HCTX_TYPE_POLL ||
> - !q->tag_set->map[HCTX_TYPE_POLL].nr_queues)
> - return -EINVAL;
> + if (queue_is_mq(q)) {
> + if (!q->tag_set || q->tag_set->nr_maps <= HCTX_TYPE_POLL ||
> + !q->tag_set->map[HCTX_TYPE_POLL].nr_queues)
> + return -EINVAL;
> + } else {
> + struct gendisk *disk = queue_to_disk(q);
> +
> + if (!disk->fops->poll_capable ||
> + !disk->fops->poll_capable(disk))
> + return -EINVAL;
> + }
>
> ret = queue_var_store(&poll_on, page, count);
> if (ret < 0)
> diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
> index 9dc83c30e7bc..7df40792c032 100644
> --- a/include/linux/blkdev.h
> +++ b/include/linux/blkdev.h
> @@ -1867,6 +1867,7 @@ static inline void blk_ksm_unregister(struct request_queue *q) { }
> struct block_device_operations {
> blk_qc_t (*submit_bio) (struct bio *bio);
> int (*poll)(struct request_queue *q, blk_qc_t cookie);
> + bool (*poll_capable)(struct gendisk *disk);
> int (*open) (struct block_device *, fmode_t);
> void (*release) (struct gendisk *, fmode_t);
> int (*rw_page)(struct block_device *, sector_t, struct page *, unsigned int);
> --
> 2.27.0
>
