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SubjectRe: [PATCH v2 1/3] block: add QUEUE_FLAG_DAX for devices to advertise their DAX support
On Thu, Jun 23, 2016 at 2:54 AM, Toshi Kani <toshi.kani@hpe.com> wrote:
>
> Currently, presence of direct_access() in block_device_operations
> indicates support of DAX on its block device. Because
> block_device_operations is instantiated with 'const', this DAX
> capablity may not be enabled conditinally.
>
> In preparation for supporting DAX to device-mapper devices, add
> QUEUE_FLAG_DAX to request_queue flags to advertise their DAX
> support. This will allow to set the DAX capability based on how
> mapped device is composed.


Hi Toshi,
This patch is very helpful!
I think QUEUE_FLAG_DAX can also help with identifying dax devices in userspace.
Perhaps you'd be willing to squash the patch below with this one or
add it to your submission?

Thanks,
Yigal


[PATCH] block: expose QUEUE_FLAG_DAX in sysfs

There's currently no way to identify DAX enabled devices in userspace.

Signed-off-by: Yigal Korman <yigal@plexistor.com>
---
block/blk-sysfs.c | 15 +++++++++++++++
1 file changed, 15 insertions(+)

diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index 9920596..d55126d 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -379,6 +379,15 @@ static ssize_t queue_wc_store(struct
request_queue *q, const char *page,
return count;
}

+static ssize_t queue_dax_show(struct request_queue *q, char *page)
+{
+ int bit;
+
+ bit = test_bit(QUEUE_FLAG_DAX, &q->queue_flags);
+
+ return queue_var_show(bit, page);
+}
+
static struct queue_sysfs_entry queue_requests_entry = {
.attr = {.name = "nr_requests", .mode = S_IRUGO | S_IWUSR },
.show = queue_requests_show,
@@ -516,6 +525,11 @@ static struct queue_sysfs_entry queue_wc_entry = {
.store = queue_wc_store,
};

+static struct queue_sysfs_entry queue_dax_entry = {
+ .attr = {.name = "dax", .mode = S_IRUGO },
+ .show = queue_dax_show,
+};
+
static struct attribute *default_attrs[] = {
&queue_requests_entry.attr,
&queue_ra_entry.attr,
@@ -542,6 +556,7 @@ static struct attribute *default_attrs[] = {
&queue_random_entry.attr,
&queue_poll_entry.attr,
&queue_wc_entry.attr,
+ &queue_dax_entry.attr,
NULL,
};

--
1.9.3
>
>
> Signed-off-by: Toshi Kani <toshi.kani@hpe.com>
> Cc: Jens Axboe <axboe@kernel.dk>
> Cc: Dan Williams <dan.j.williams@intel.com>
> Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
> Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
> Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
> Cc: <linux-s390@vger.kernel.org>
> ---
> drivers/block/brd.c | 4 +++-
> drivers/nvdimm/pmem.c | 1 +
> drivers/s390/block/dcssblk.c | 1 +
> fs/block_dev.c | 5 +++--
> include/linux/blkdev.h | 2 ++
> 5 files changed, 10 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/block/brd.c b/drivers/block/brd.c
> index f5b0d6f..dd96a93 100644
> --- a/drivers/block/brd.c
> +++ b/drivers/block/brd.c
> @@ -509,7 +509,9 @@ static struct brd_device *brd_alloc(int i)
> blk_queue_max_discard_sectors(brd->brd_queue, UINT_MAX);
> brd->brd_queue->limits.discard_zeroes_data = 1;
> queue_flag_set_unlocked(QUEUE_FLAG_DISCARD, brd->brd_queue);
> -
> +#ifdef CONFIG_BLK_DEV_RAM_DAX
> + queue_flag_set_unlocked(QUEUE_FLAG_DAX, brd->brd_queue);
> +#endif
> disk = brd->brd_disk = alloc_disk(max_part);
> if (!disk)
> goto out_free_queue;
> diff --git a/drivers/nvdimm/pmem.c b/drivers/nvdimm/pmem.c
> index 608fc44..53b701b 100644
> --- a/drivers/nvdimm/pmem.c
> +++ b/drivers/nvdimm/pmem.c
> @@ -283,6 +283,7 @@ static int pmem_attach_disk(struct device *dev,
> blk_queue_max_hw_sectors(q, UINT_MAX);
> blk_queue_bounce_limit(q, BLK_BOUNCE_ANY);
> queue_flag_set_unlocked(QUEUE_FLAG_NONROT, q);
> + queue_flag_set_unlocked(QUEUE_FLAG_DAX, q);
> q->queuedata = pmem;
>
> disk = alloc_disk_node(0, nid);
> diff --git a/drivers/s390/block/dcssblk.c b/drivers/s390/block/dcssblk.c
> index bed53c4..093e9e1 100644
> --- a/drivers/s390/block/dcssblk.c
> +++ b/drivers/s390/block/dcssblk.c
> @@ -618,6 +618,7 @@ dcssblk_add_store(struct device *dev, struct device_attribute *attr, const char
> dev_info->gd->driverfs_dev = &dev_info->dev;
> blk_queue_make_request(dev_info->dcssblk_queue, dcssblk_make_request);
> blk_queue_logical_block_size(dev_info->dcssblk_queue, 4096);
> + queue_flag_set_unlocked(QUEUE_FLAG_DAX, dev_info->dcssblk_queue);
>
> seg_byte_size = (dev_info->end - dev_info->start + 1);
> set_capacity(dev_info->gd, seg_byte_size >> 9); // size in sectors
> diff --git a/fs/block_dev.c b/fs/block_dev.c
> index 71ccab1..d012be4 100644
> --- a/fs/block_dev.c
> +++ b/fs/block_dev.c
> @@ -493,7 +493,7 @@ long bdev_direct_access(struct block_device *bdev, struct blk_dax_ctl *dax)
>
> if (size < 0)
> return size;
> - if (!ops->direct_access)
> + if (!blk_queue_dax(bdev_get_queue(bdev)) || !ops->direct_access)
> return -EOPNOTSUPP;
> if ((sector + DIV_ROUND_UP(size, 512)) >
> part_nr_sects_read(bdev->bd_part))
> @@ -1287,7 +1287,8 @@ static int __blkdev_get(struct block_device *bdev, fmode_t mode, int for_part)
> bdev->bd_disk = disk;
> bdev->bd_queue = disk->queue;
> bdev->bd_contains = bdev;
> - if (IS_ENABLED(CONFIG_BLK_DEV_DAX) && disk->fops->direct_access)
> + if (IS_ENABLED(CONFIG_BLK_DEV_DAX) &&
> + blk_queue_dax(disk->queue))
> bdev->bd_inode->i_flags = S_DAX;
> else
> bdev->bd_inode->i_flags = 0;
> diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
> index 9746d22..1493ab3 100644
> --- a/include/linux/blkdev.h
> +++ b/include/linux/blkdev.h
> @@ -505,6 +505,7 @@ struct request_queue {
> #define QUEUE_FLAG_WC 23 /* Write back caching */
> #define QUEUE_FLAG_FUA 24 /* device supports FUA writes */
> #define QUEUE_FLAG_FLUSH_NQ 25 /* flush not queueuable */
> +#define QUEUE_FLAG_DAX 26 /* device supports DAX */
>
> #define QUEUE_FLAG_DEFAULT ((1 << QUEUE_FLAG_IO_STAT) | \
> (1 << QUEUE_FLAG_STACKABLE) | \
> @@ -594,6 +595,7 @@ static inline void queue_flag_clear(unsigned int flag, struct request_queue *q)
> #define blk_queue_discard(q) test_bit(QUEUE_FLAG_DISCARD, &(q)->queue_flags)
> #define blk_queue_secdiscard(q) (blk_queue_discard(q) && \
> test_bit(QUEUE_FLAG_SECDISCARD, &(q)->queue_flags))
> +#define blk_queue_dax(q) test_bit(QUEUE_FLAG_DAX, &(q)->queue_flags)
>
> #define blk_noretry_request(rq) \
> ((rq)->cmd_flags & (REQ_FAILFAST_DEV|REQ_FAILFAST_TRANSPORT| \
> _______________________________________________
> Linux-nvdimm mailing list
> Linux-nvdimm@lists.01.org
> https://lists.01.org/mailman/listinfo/linux-nvdimm

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