linux-kernel - [PATCH V4 16/17] block: ublk_drv: don't check buffer in case of zero copy

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Date:   Fri, 24 Mar 2023 21:58:07 +0800
From:   Ming Lei <ming.lei@...hat.com>
To:     Jens Axboe <axboe@...nel.dk>, io-uring@...r.kernel.org,
        linux-block@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, Miklos Szeredi <mszeredi@...hat.com>,
        ZiyangZhang <ZiyangZhang@...ux.alibaba.com>,
        Xiaoguang Wang <xiaoguang.wang@...ux.alibaba.com>,
        Bernd Schubert <bschubert@....com>,
        Pavel Begunkov <asml.silence@...il.com>,
        Stefan Hajnoczi <stefanha@...hat.com>,
        Ming Lei <ming.lei@...hat.com>
Subject: [PATCH V4 16/17] block: ublk_drv: don't check buffer in case of zero copy

In case of zero copy, ublk server needn't to pre-allocate IO buffer
and provide it to driver more.

Meantime not set the buffer in case of zero copy any more, and the
userspace can use pread()/pwrite() to read from/write to the io request
buffer, which is easier & simpler from userspace viewpoint.

Signed-off-by: Ming Lei <ming.lei@...hat.com>
---
 drivers/block/ublk_drv.c | 23 ++++++++++++++---------
 1 file changed, 14 insertions(+), 9 deletions(-)

diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c
index e6b528750b3c..979444647831 100644
--- a/drivers/block/ublk_drv.c
+++ b/drivers/block/ublk_drv.c
@@ -1405,25 +1405,30 @@ static int ublk_ch_uring_cmd(struct io_uring_cmd *cmd, unsigned int issue_flags)
 		if (io->flags & UBLK_IO_FLAG_OWNED_BY_SRV)
 			goto out;
 		/* FETCH_RQ has to provide IO buffer if NEED GET DATA is not enabled */
-		if (!ub_cmd->addr && !ublk_need_get_data(ubq))
-			goto out;
+		if (!ublk_support_zc(ubq)) {
+			if (!ub_cmd->addr && !ublk_need_get_data(ubq))
+				goto out;
+			io->addr = ub_cmd->addr;
+		}
 		io->cmd = cmd;
 		io->flags |= UBLK_IO_FLAG_ACTIVE;
-		io->addr = ub_cmd->addr;
-
 		ublk_mark_io_ready(ub, ubq);
 		break;
 	case UBLK_IO_COMMIT_AND_FETCH_REQ:
 		req = blk_mq_tag_to_rq(ub->tag_set.tags[ub_cmd->q_id], tag);
+
+		if (!(io->flags & UBLK_IO_FLAG_OWNED_BY_SRV))
+			goto out;
 		/*
 		 * COMMIT_AND_FETCH_REQ has to provide IO buffer if NEED GET DATA is
 		 * not enabled or it is Read IO.
 		 */
-		if (!ub_cmd->addr && (!ublk_need_get_data(ubq) || req_op(req) == REQ_OP_READ))
-			goto out;
-		if (!(io->flags & UBLK_IO_FLAG_OWNED_BY_SRV))
-			goto out;
-		io->addr = ub_cmd->addr;
+		if (!ublk_support_zc(ubq)) {
+			if (!ub_cmd->addr && (!ublk_need_get_data(ubq) ||
+						req_op(req) == REQ_OP_READ))
+				goto out;
+			io->addr = ub_cmd->addr;
+		}
 		io->flags |= UBLK_IO_FLAG_ACTIVE;
 		io->cmd = cmd;
 		ublk_commit_completion(ub, ub_cmd);
-- 
2.39.2