[PATCH v4 07/10] scsi: scsi_debug: Do not write a partial physical block to a zoned device

[Niklas Cassel <cassel@kernel.org>]

do_device_access() copies one logical block at a time and stops at the
first short copy, so when the data-out buffer is smaller than the
transfer length of the command it can write part of a physical block.
An initiator can arrange that with SG_IO.

A write that does not end on a physical block boundary is perfectly
acceptable to a device that is not zoned, and to a conventional zone,
where the device reads, modifies and writes the physical block that the
write falls in. ZBC-3 r06 (T10/BSR INCITS 579), 4.5.3.3.2, does require
a write to a sequential write required zone to end on a physical block
boundary, though, so a partly written physical block is not a state that
such a zone can be left in.

Stop at the last whole physical block that the buffer holds, for a
sequential write required zone only. The bytes that are left over are
not written, and are reported to the initiator as part of the residual.

With the default physblk_exp=0 the physical block size equals the
logical block size and this changes nothing. Nothing changes either when
the buffer holds all of the data that the command asks for, so a command
that transfers fewer logical blocks than a physical block is unaffected
wherever it is legal.

Assisted-by: LLM
Signed-off-by: Niklas Cassel <cassel@kernel.org>
---
Tested with:

  modprobe scsi_debug zbc=managed sector_size=512 physblk_exp=3 \
      zone_size_mb=8 dev_size_mb=128 zone_nr_conv=2

issuing a sixteen logical block WRITE(16) through SG_IO with a buffer of
twelve blocks. To a sequential write required zone it now transfers
eight blocks, one whole physical block, and reports the remaining 2048
bytes as the residual; before this patch it transferred twelve. To a
conventional zone it still transfers all twelve and reports no residual.

With physblk_exp=0 an eight block write with a buffer of one block still
transfers one block, wherever it is addressed.
---
 drivers/scsi/scsi_debug.c | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/drivers/scsi/scsi_debug.c b/drivers/scsi/scsi_debug.c
index a4db282ac971..837077a4e740 100644
--- a/drivers/scsi/scsi_debug.c
+++ b/drivers/scsi/scsi_debug.c
@@ -4273,6 +4273,8 @@ static int do_device_access(struct sdeb_store_info *sip, struct scsi_cmnd *scp,
 	u64 block;
 	enum dma_data_direction dir;
 	struct scsi_data_buffer *sdb = &scp->sdb;
+	struct scsi_device *sdp = scp->device;
+	struct sdebug_dev_info *devip = (struct sdebug_dev_info *)sdp->hostdata;
 	u8 *fsp;
 	int i, total = 0;
 
@@ -4300,6 +4302,24 @@ static int do_device_access(struct sdeb_store_info *sip, struct scsi_cmnd *scp,
 
 	fsp = sip->storep;
 
+	/*
+	 * A write to a sequential write required zone has to end on a physical
+	 * block boundary, so if the data-out buffer does not hold all of the
+	 * data that the command asks for, write up to the last whole physical
+	 * block that it does hold. What is left over is reported as part of
+	 * the residual.
+	 */
+	if (do_write && sdebug_dev_is_zoned(devip)) {
+		struct sdeb_zone_state *zsp = zbc_zone(devip, lba);
+
+		if (zsp->z_type == ZBC_ZTYPE_SWR) {
+			u32 avail = (sdb->length - sg_skip) / sdebug_sector_size;
+
+			if (avail < num)
+				num = round_down(avail, 1U << sdebug_physblk_exp);
+		}
+	}
+
 	block = do_div(lba, sdebug_store_sectors);
 
 	/* Only allow 1x atomic write or multiple non-atomic writes at any given time */
-- 
2.55.0