[RFC PATCH 5/6] scsi mid layer support for async command submit

[David Jeffery <djeffery@redhat.com>]

Create scsi_execute_cmd_nowait to allow asynchronous scsi command submit.
Parts of the code originally in scsi_execute_cmd are shifted into helper
functions used by both scsi_execute_cmd and the new scsi_execute_cmd_nowait.

The scsi_exec_args struct is expanded to contain the fields needed for
the completion and callback for the async path.

Signed-off-by: David Jeffery <djeffery@redhat.com>
Tested-by:     Laurence Oberman <loberman@redhat.com>

---
 drivers/scsi/scsi_lib.c    | 138 +++++++++++++++++++++++++++++--------
 include/scsi/scsi_device.h |   8 +++
 2 files changed, 118 insertions(+), 28 deletions(-)

diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index 1fb80eae9a63..fe35bc2021e3 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -185,42 +185,37 @@ void scsi_queue_insert(struct scsi_cmnd *cmd, int reason)
 }
 
 /**
- * scsi_execute_cmd - insert request and wait for the result
+ * scsi_execute_init - helper for setting up a scsi_cmnd in a request
  * @sdev:	scsi_device
  * @cmd:	scsi command
  * @opf:	block layer request cmd_flags
- * @buffer:	data buffer
- * @bufflen:	len of buffer
  * @timeout:	request timeout in HZ
  * @retries:	number of times to retry request
- * @args:	Optional args. See struct definition for field descriptions
+ * @args:	scsi command args
  *
- * Returns the scsi_cmnd result field if a command was executed, or a negative
- * Linux error code if we didn't get that far.
+ * Returns a request if successful, or an error pointer if there was a failure.
  */
-int scsi_execute_cmd(struct scsi_device *sdev, const unsigned char *cmd,
-		     blk_opf_t opf, void *buffer, unsigned int bufflen,
-		     int timeout, int retries,
-		     const struct scsi_exec_args *args)
+static struct request *scsi_execute_init(struct scsi_device *sdev,
+					 const unsigned char *cmd,
+					 blk_opf_t opf,
+					 int timeout, int retries,
+					 struct scsi_exec_args *args)
 {
-	static const struct scsi_exec_args default_args;
 	struct request *req;
 	struct scsi_cmnd *scmd;
 	int ret;
 
-	if (!args)
-		args = &default_args;
-	else if (WARN_ON_ONCE(args->sense &&
-			      args->sense_len != SCSI_SENSE_BUFFERSIZE))
-		return -EINVAL;
+	if (WARN_ON_ONCE(args->sense &&
+			 args->sense_len != SCSI_SENSE_BUFFERSIZE))
+		return ERR_PTR(-EINVAL);
 
 	req = scsi_alloc_request(sdev->request_queue, opf, args->req_flags);
 	if (IS_ERR(req))
-		return PTR_ERR(req);
+		return req;
 
-	if (bufflen) {
-		ret = blk_rq_map_kern(sdev->request_queue, req,
-				      buffer, bufflen, GFP_NOIO);
+	if (args->bufflen) {
+		ret = blk_rq_map_kern(sdev->request_queue, req, args->buffer,
+				      args->bufflen, GFP_NOIO);
 		if (ret)
 			goto out;
 	}
@@ -232,19 +227,27 @@ int scsi_execute_cmd(struct scsi_device *sdev, const unsigned char *cmd,
 	req->timeout = timeout;
 	req->rq_flags |= RQF_QUIET;
 
-	/*
-	 * head injection *required* here otherwise quiesce won't work
-	 */
-	blk_execute_rq(req, true);
+	return req;
+out:
+	blk_mq_free_request(req);
+	return ERR_PTR(ret);
+}
+
+static int scsi_execute_uninit(struct request *req,
+				struct scsi_exec_args *args)
+{
+	struct scsi_cmnd *scmd;
 
+	scmd = blk_mq_rq_to_pdu(req);
 	/*
 	 * Some devices (USB mass-storage in particular) may transfer
 	 * garbage data together with a residue indicating that the data
 	 * is invalid.  Prevent the garbage from being misinterpreted
 	 * and prevent security leaks by zeroing out the excess data.
 	 */
-	if (unlikely(scmd->resid_len > 0 && scmd->resid_len <= bufflen))
-		memset(buffer + bufflen - scmd->resid_len, 0, scmd->resid_len);
+	if (unlikely(scmd->resid_len > 0 && scmd->resid_len <= args->bufflen))
+		memset(args->buffer + args->bufflen - scmd->resid_len, 0,
+		       scmd->resid_len);
 
 	if (args->resid)
 		*args->resid = scmd->resid_len;
@@ -254,14 +257,93 @@ int scsi_execute_cmd(struct scsi_device *sdev, const unsigned char *cmd,
 		scsi_normalize_sense(scmd->sense_buffer, scmd->sense_len,
 				     args->sshdr);
 
-	ret = scmd->result;
- out:
+	args->result = scmd->result;
+
+	if (args->callback)
+		args->callback(scmd, args);
+
+	return scmd->result;
+}
+
+/**
+ * scsi_execute_cmd - insert request and wait for the result
+ * @sdev:	scsi_device
+ * @cmd:	scsi command
+ * @opf:	block layer request cmd_flags
+ * @buffer:	data buffer
+ * @bufflen:	len of buffer
+ * @timeout:	request timeout in HZ
+ * @retries:	number of times to retry request
+ * @args:	Optional args. See struct definition for field descriptions
+ *
+ * Returns the scsi_cmnd result field if a command was executed, or a negative
+ * Linux error code if we didn't get that far.
+ */
+int scsi_execute_cmd(struct scsi_device *sdev, const unsigned char *cmd,
+		     blk_opf_t opf, void *buffer, unsigned int bufflen,
+		     int timeout, int retries,
+		     const struct scsi_exec_args *const_args)
+{
+	struct scsi_exec_args args;
+	int ret;
+	struct request *req;
+
+	if (!const_args)
+		memset(&args, 0, sizeof(struct scsi_exec_args));
+	else
+		args = *const_args;
+
+	args.buffer = buffer;
+	args.bufflen = bufflen;
+
+	req = scsi_execute_init(sdev, cmd, opf, timeout, retries, &args);
+
+	if (IS_ERR(req))
+		return PTR_ERR(req);
+
+	/*
+	 * head injection *required* here otherwise quiesce won't work
+	 */
+	blk_execute_rq(req, true);
+
+	ret = scsi_execute_uninit(req, &args);
+
 	blk_mq_free_request(req);
 
 	return ret;
 }
 EXPORT_SYMBOL(scsi_execute_cmd);
 
+
+static enum rq_end_io_ret scsi_execute_cmd_complete(struct request *req,
+						    blk_status_t ret)
+{
+	struct scsi_exec_args *args = req->end_io_data;
+
+	scsi_execute_uninit(req, args);
+	return RQ_END_IO_FREE;
+}
+
+int scsi_execute_cmd_nowait(struct scsi_device *sdev, const unsigned char *cmd,
+			    blk_opf_t opf, int timeout, int retries,
+			    struct scsi_exec_args *args)
+{
+	struct request *req;
+
+	req = scsi_execute_init(sdev, cmd, opf, timeout, retries, args);
+
+	if (IS_ERR(req))
+		return PTR_ERR(req);
+
+	req->end_io = scsi_execute_cmd_complete;
+	req->end_io_data = args;
+
+	blk_execute_rq_nowait(req, true);
+
+	return 0;
+}
+EXPORT_SYMBOL(scsi_execute_cmd_nowait);
+
 /*
  * Wake up the error handler if necessary. Avoid as follows that the error
  * handler is not woken up if host in-flight requests number ==
diff --git a/include/scsi/scsi_device.h b/include/scsi/scsi_device.h
index 5ec1e71a09de..c80c98b48bc1 100644
--- a/include/scsi/scsi_device.h
+++ b/include/scsi/scsi_device.h
@@ -497,6 +497,10 @@ struct scsi_exec_args {
 	blk_mq_req_flags_t req_flags;	/* BLK_MQ_REQ flags */
 	int scmd_flags;			/* SCMD flags */
 	int *resid;			/* residual length */
+	void *buffer;			/* data buffer */
+	unsigned int bufflen;		/* buffer length */
+	int result;			/* scsi layer result */
+	void (*callback)(struct scsi_cmnd *scmd, struct scsi_exec_args *args);
 };
 
 int scsi_execute_cmd(struct scsi_device *sdev, const unsigned char *cmd,
@@ -504,6 +508,10 @@ int scsi_execute_cmd(struct scsi_device *sdev, const unsigned char *cmd,
 		     int timeout, int retries,
 		     const struct scsi_exec_args *args);
 
+int scsi_execute_cmd_nowait(struct scsi_device *sdev, const unsigned char *cmd,
+			    blk_opf_t opf, int timeout, int retries,
+			    struct scsi_exec_args *args);
+
 extern void sdev_disable_disk_events(struct scsi_device *sdev);
 extern void sdev_enable_disk_events(struct scsi_device *sdev);
 extern int scsi_vpd_lun_id(struct scsi_device *, char *, size_t);
-- 
2.43.0