[PATCH v3] nvmet: handle rw's limited retry flag

[Guixin Liu]

In some scenarios, some multipath software setup places the
REQ_FAILFAST_DEV flag on I/O to prevent retries and immediately
switch to other paths for issuing I/O commands. This will reflect
on the NVMe read and write commands with the limited retry flag.

However, the current NVMe target side does not handle the limited
retry flag, and the target's underlying driver still retries the
I/O. This will result in the I/O not being quickly switched to
other paths, ultimately leading to increased I/O latency.

When the nvme target receive an rw command with limited retry flag,
handle it in block backend by setting the REQ_FAILFAST_DEV flag to
bio.

Signed-off-by: Guixin Liu <kanie at linux.alibaba.com>
Reviewed-by: Chaitanya Kulkarni <kch at nvidia.com>
Reviewed-by: Christoph Hellwig <hch at lst.de>
---
Changes from v2 to v3:
- Add the rb tag from Christoph, thanks.

Changes from v1 to v2:
- Add details to commit body(Christoph).
- Add the rb tag from Chaitanya, thanks.

 drivers/nvme/target/io-cmd-bdev.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/nvme/target/io-cmd-bdev.c b/drivers/nvme/target/io-cmd-bdev.c
index 0bda83d0fc3e..6380b60fd490 100644
--- a/drivers/nvme/target/io-cmd-bdev.c
+++ b/drivers/nvme/target/io-cmd-bdev.c
@@ -272,6 +272,9 @@ static void nvmet_bdev_execute_rw(struct nvmet_req *req)
 		iter_flags = SG_MITER_FROM_SG;
 	}
 
+	if (req->cmd->rw.control & NVME_RW_LR)
+		opf |= REQ_FAILFAST_DEV;
+
 	if (is_pci_p2pdma_page(sg_page(req->sg)))
 		opf |= REQ_NOMERGE;
 
-- 
2.43.0