linux-kernel - [PATCH v2 4/5] block nbd: use req.cookie instead of req.handle

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Date:   Fri, 17 Mar 2023 15:27:48 -0500
From:   Eric Blake <eblake@...hat.com>
To:     josef@...icpanda.com, linux-block@...r.kernel.org,
        nbd@...er.debian.org
Cc:     philipp.reisner@...bit.com, lars.ellenberg@...bit.com,
        christoph.boehmwalder@...bit.com, corbet@....net,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH v2 4/5] block nbd: use req.cookie instead of req.handle

A good optimizing compiler should not compile this any differently,
but it is nicer to work directly with integers instead of memcpy().

Signed-off-by: Eric Blake <eblake@...hat.com>

---
v2: Fix kernel test robot complaint about wrong endianness on loongarch:
https://lore.kernel.org/oe-kbuild-all/202303121323.Jd35Q1Au-lkp@intel.com/
---
 drivers/block/nbd.c | 8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
index 8a9487e79f1c..94ae85400b46 100644
--- a/drivers/block/nbd.c
+++ b/drivers/block/nbd.c
@@ -560,7 +560,6 @@ static int nbd_send_cmd(struct nbd_device *nbd, struct nbd_cmd *cmd, int index)
 	unsigned long size = blk_rq_bytes(req);
 	struct bio *bio;
 	u64 handle;
-	__be64 tmp;
 	u32 type;
 	u32 nbd_cmd_flags = 0;
 	int sent = nsock->sent, skip = 0;
@@ -607,8 +606,7 @@ static int nbd_send_cmd(struct nbd_device *nbd, struct nbd_cmd *cmd, int index)
 		request.len = htonl(size);
 	}
 	handle = nbd_cmd_handle(cmd);
-	tmp = cpu_to_be64(handle);
-	memcpy(request.handle, &tmp, sizeof(tmp));
+	request.cookie = cpu_to_be64(handle);

 	trace_nbd_send_request(&request, nbd->index, blk_mq_rq_from_pdu(cmd));

@@ -729,14 +727,12 @@ static struct nbd_cmd *nbd_handle_reply(struct nbd_device *nbd, int index,
 	int result;
 	struct nbd_cmd *cmd;
 	struct request *req = NULL;
-	__be64 tmp;
 	u64 handle;
 	u16 hwq;
 	u32 tag;
 	int ret = 0;

-	memcpy(&tmp, reply->handle, sizeof(tmp));
-	handle = be64_to_cpu(tmp);
+	handle = be64_to_cpu(reply->cookie);
 	tag = nbd_handle_to_tag(handle);
 	hwq = blk_mq_unique_tag_to_hwq(tag);
 	if (hwq < nbd->tag_set.nr_hw_queues)
-- 
2.39.2