On Mon, 2017-04-10 at 18:08 +0200, Christoph Hellwig wrote:
> Use the pscsi driver to support arbitrary command passthrough
> instead.
>
The people who are actively using iblock_execute_write_same_direct() are
doing so in the context of ESX VAAI BlockZero, together with
EXTENDED_COPY and COMPARE_AND_WRITE primitives. Just using PSCSI is not
an option for them.
In practice though I've not seen any users of IBLOCK WRITE_SAME for
anything other than VAAI BlockZero, so just using blkdev_issue_zeroout()
when available, and falling back to iblock_execute_write_same() if the
WRITE_SAME buffer contains anything other than zeros should be OK.
How about something like the following below..?
This would bring parity to how blkdev_issue_write_same() works atm wrt
to synchronous bio completions. However, most folks with a raw
make_request or blk-mq backend driver that supports multiple GB/sec of
zero bandwidth end up changing IBLOCK to support asynchronous
REQ_WRITE_SAME completions anyways.
I'd be happy to add support for that using __blkdev_issue_zeroout() once
the basic conversion is in place.
>From ff74012eaff38f9fa0d74aca60507b9964f484ce Mon Sep 17 00:00:00 2001
From: Nicholas Bellinger <nab@xxxxxxxxxxxxxxx>
Date: Tue, 11 Apr 2017 22:21:47 -0700
Subject: [PATCH] target/iblock: Convert WRITE_SAME to blkdev_issue_zeroout
Signed-off-by: Nicholas Bellinger <nab@xxxxxxxxxxxxxxx>
---
drivers/target/target_core_iblock.c | 44 +++++++++++++++++++++++--------------
1 file changed, 27 insertions(+), 17 deletions(-)
diff --git a/drivers/target/target_core_iblock.c b/drivers/target/target_core_iblock.c
index d316ed5..5bfde20 100644
--- a/drivers/target/target_core_iblock.c
+++ b/drivers/target/target_core_iblock.c
@@ -86,6 +86,7 @@ static int iblock_configure_device(struct se_device *dev)
struct block_device *bd = NULL;
struct blk_integrity *bi;
fmode_t mode;
+ unsigned int max_write_zeroes_sectors;
int ret = -ENOMEM;
if (!(ib_dev->ibd_flags & IBDF_HAS_UDEV_PATH)) {
@@ -129,7 +130,11 @@ static int iblock_configure_device(struct se_device *dev)
* Enable write same emulation for IBLOCK and use 0xFFFF as
* the smaller WRITE_SAME(10) only has a two-byte block count.
*/
- dev->dev_attrib.max_write_same_len = 0xFFFF;
+ max_write_zeroes_sectors = bdev_write_zeroes_sectors(bd);
+ if (max_write_zeroes_sectors)
+ dev->dev_attrib.max_write_same_len = max_write_zeroes_sectors;
+ else
+ dev->dev_attrib.max_write_same_len = 0xFFFF;
if (blk_queue_nonrot(q))
dev->dev_attrib.is_nonrot = 1;
@@ -415,28 +420,31 @@ static void iblock_end_io_flush(struct bio *bio)
}
static sense_reason_t
-iblock_execute_write_same_direct(struct block_device *bdev, struct se_cmd *cmd)
+iblock_execute_zero_out(struct block_device *bdev, struct se_cmd *cmd)
{
struct se_device *dev = cmd->se_dev;
struct scatterlist *sg = &cmd->t_data_sg[0];
- struct page *page = NULL;
- int ret;
+ unsigned char *buf, zero = 0x00, *p = &zero;
+ int rc, ret;
- if (sg->offset) {
- page = alloc_page(GFP_KERNEL);
- if (!page)
- return TCM_OUT_OF_RESOURCES;
- sg_copy_to_buffer(sg, cmd->t_data_nents, page_address(page),
- dev->dev_attrib.block_size);
- }
+ buf = kmap(sg_page(sg)) + sg->offset;
+ if (!buf)
+ return TCM_LOGICAL_UNIT_COMMUNICATION_FAILURE;
+ /*
+ * Fall back to block_execute_write_same() slow-path if
+ * incoming WRITE_SAME payload does not contain zeros.
+ */
+ rc = memcmp(buf, p, cmd->data_length);
+ kunmap(sg_page(sg));
+
+ if (rc)
+ return TCM_LOGICAL_UNIT_COMMUNICATION_FAILURE;
- ret = blkdev_issue_write_same(bdev,
+ ret = blkdev_issue_zeroout(bdev,
target_to_linux_sector(dev, cmd->t_task_lba),
target_to_linux_sector(dev,
sbc_get_write_same_sectors(cmd)),
- GFP_KERNEL, page ? page : sg_page(sg));
- if (page)
- __free_page(page);
+ GFP_KERNEL, false);
if (ret)
return TCM_LOGICAL_UNIT_COMMUNICATION_FAILURE;
@@ -472,8 +480,10 @@ static void iblock_end_io_flush(struct bio *bio)
return TCM_INVALID_CDB_FIELD;
}
- if (bdev_write_same(bdev))
- return iblock_execute_write_same_direct(bdev, cmd);
+ if (bdev_write_zeroes_sectors(bdev)) {
+ if (!iblock_execute_zero_out(bdev, cmd))
+ return 0;
+ }
ibr = kzalloc(sizeof(struct iblock_req), GFP_KERNEL);
if (!ibr)
--
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