[PATCH 1/2] [tgt]: Add proper CDB passthrough for SG_IO backstores

["Nicholas A. Bellinger" <nab@linux-iscsi.org>]

From: Nicholas Bellinger <nab@linux-iscsi.org>

This patch updates usr/bs_sg.c:bs_sg_cmd_submit() to process incoming scsi-generic IO
of type SG_DXFER_TO_DEV and SG_DXFER_FROM_DEV using a single new struct scsi_cmnd->sg_iovec
set using existing scsi_cmd.h scsi_get_[out,in]_[buffer,length]() macros.

It also makes set_cmd_failed() properly return SAM_STAT_CHECK_CONDITION, which is expected
by the bs_sg_cmd_submit() caller in usr/scsi.c:scsi_cmd_perform()

Finally, this patch adds struct backingstore_template->bs_passthrough=1 that is used by
bs_sg.c here and the next patch to hand off struct scsi_cmd for CDB passthrough.

Signed-off-by: Nicholas A. Bellinger <nab@linux-iscsi.org>
---
 usr/bs_sg.c     |   31 ++++++++++++++++++++++++-------
 usr/scsi_cmnd.h |    4 ++++
 usr/tgtd.h      |    1 +
 3 files changed, 29 insertions(+), 7 deletions(-)

diff --git a/usr/bs_sg.c b/usr/bs_sg.c
index 8baa480..9696392 100644
--- a/usr/bs_sg.c
+++ b/usr/bs_sg.c
@@ -82,7 +82,7 @@ static int graceful_write(int fd, void *p_write, int to_write)
 	return 0;
 }
 
-static void set_cmd_failed(struct scsi_cmd *cmd)
+static int set_cmd_failed(struct scsi_cmd *cmd)
 {
 	int result = SAM_STAT_CHECK_CONDITION;
 	uint16_t asc = ASC_READ_ERROR;
@@ -90,11 +90,14 @@ static void set_cmd_failed(struct scsi_cmd *cmd)
 
 	scsi_set_result(cmd, result);
 	sense_data_build(cmd, key, asc);
+
+	return result;
 }
 
 static int bs_sg_cmd_submit(struct scsi_cmd *cmd)
 {
 	struct scsi_lu *dev = cmd->dev;
+	struct sg_iovec *iov = &cmd->sg_iovec;
 	int fd = dev->fd;
 	struct sg_io_hdr io_hdr;
 	int err = 0;
@@ -104,14 +107,27 @@ static int bs_sg_cmd_submit(struct scsi_cmd *cmd)
 	io_hdr.cmd_len = cmd->scb_len;
 	io_hdr.cmdp = cmd->scb;
 
+	if (scsi_get_data_dir(cmd) == DATA_BIDIRECTIONAL) {
+		eprintf("Unable to process DATA_BIDIRECTIONAL to"
+			" SG_IO backstore\n");
+		return set_cmd_failed(cmd);
+	}
+
 	if (scsi_get_data_dir(cmd) == DATA_WRITE) {
 		io_hdr.dxfer_direction = SG_DXFER_TO_DEV;
-		io_hdr.dxfer_len = scsi_get_out_length(cmd);
-		io_hdr.dxferp = (void *)scsi_get_out_buffer(cmd);
-	} else {
+		io_hdr.dxfer_len = iov->iov_len = scsi_get_out_length(cmd);
+		iov->iov_base = (void *)scsi_get_out_buffer(cmd);
+		io_hdr.dxferp = &cmd->sg_iovec;
+		io_hdr.iovec_count = 1;
+	} else if (scsi_get_data_dir(cmd) == DATA_READ) {
 		io_hdr.dxfer_direction = SG_DXFER_FROM_DEV;
-		io_hdr.dxfer_len = scsi_get_in_length(cmd);
-		io_hdr.dxferp = (void *)scsi_get_in_buffer(cmd);
+		io_hdr.dxfer_len = iov->iov_len = scsi_get_in_length(cmd);
+		iov->iov_base = (void *)scsi_get_in_buffer(cmd);
+		io_hdr.dxferp = &cmd->sg_iovec;
+		io_hdr.iovec_count = 1;
+	} else {
+		io_hdr.dxfer_direction = SG_DXFER_NONE;
+		io_hdr.dxfer_len = 0;
 	}
 	io_hdr.mx_sb_len = sizeof(cmd->sense_buffer);
 	io_hdr.sbp = cmd->sense_buffer;
@@ -125,7 +141,7 @@ static int bs_sg_cmd_submit(struct scsi_cmd *cmd)
 		set_cmd_async(cmd);
 	else {
 		eprintf("failed to start cmd 0x%p\n", cmd);
-		set_cmd_failed(cmd);
+		return set_cmd_failed(cmd);
 	}
 	return 0;
 }
@@ -238,6 +254,7 @@ static int bs_sg_cmd_done(struct scsi_cmd *cmd)
 static struct backingstore_template sg_bst = {
 	.bs_name		= "sg",
 	.bs_datasize		= 0,
+	.bs_passthrough		= 1,
 	.bs_open		= bs_sg_open,
 	.bs_close		= bs_sg_close,
 	.bs_cmd_submit		= bs_sg_cmd_submit,
diff --git a/usr/scsi_cmnd.h b/usr/scsi_cmnd.h
index 011f3e6..776ffb3 100644
--- a/usr/scsi_cmnd.h
+++ b/usr/scsi_cmnd.h
@@ -17,6 +17,8 @@ struct scsi_data_buffer {
 	uint64_t buffer;
 };
 
+#include <scsi/sg.h>
+
 struct scsi_cmd {
 	struct target *c_target;
 	/* linked it_nexus->cmd_hash_list */
@@ -31,6 +33,8 @@ struct scsi_cmd {
 	enum data_direction data_dir;
 	struct scsi_data_buffer in_sdb;
 	struct scsi_data_buffer out_sdb;
+	/* used for bs_sg.c:bs_sg_cmd_submit() */
+	struct sg_iovec sg_iovec;
 
 	uint64_t cmd_itn_id;
 	uint64_t offset;
diff --git a/usr/tgtd.h b/usr/tgtd.h
index 3323a9b..4f26a29 100644
--- a/usr/tgtd.h
+++ b/usr/tgtd.h
@@ -117,6 +117,7 @@ struct device_type_template {
 struct backingstore_template {
 	const char *bs_name;
 	int bs_datasize;
+	int bs_passthrough;
 	int (*bs_open)(struct scsi_lu *dev, char *path, int *fd, uint64_t *size);
 	void (*bs_close)(struct scsi_lu *dev);
 	int (*bs_init)(struct scsi_lu *dev);
-- 
1.5.6.5