scsi: Implement blk_mq_ops.show_rq()

Show the SCSI CDB for pending SCSI commands in
/sys/kernel/debug/block/*/mq/*/dispatch and */rq_list. An example
of how SCSI commands are displayed by this code:

ffff8801703245c0 {.op=READ, .cmd_flags=META PRIO, .rq_flags=DONTPREP IO_STAT STATS, .tag=14, .internal_tag=-1, .cmd=Read(10) 28 00 2a 81 1b 30 00 00 08 00}

Signed-off-by: Bart Van Assche <[e-mail]>
Reviewed-by: Omar Sandoval <[e-mail]>
Cc: Martin K. Petersen <[e-mail]>
Cc: James Bottomley <[e-mail]>
Cc: Hannes Reinecke <[e-mail]>
Cc: <[e-mail]>
Signed-off-by: Jens Axboe <[e-mail]>

drivers/scsi/Makefile

···
 scsi_mod-$(CONFIG_SCSI_NETLINK)	+= scsi_netlink.o
 scsi_mod-$(CONFIG_SYSCTL)	+= scsi_sysctl.o
 scsi_mod-$(CONFIG_SCSI_PROC_FS)	+= scsi_proc.o
+scsi_mod-$(CONFIG_BLK_DEBUG_FS)	+= scsi_debugfs.o
 scsi_mod-y			+= scsi_trace.o scsi_logging.o
 scsi_mod-$(CONFIG_PM)		+= scsi_pm.o
 scsi_mod-$(CONFIG_SCSI_DH)	+= scsi_dh.o

drivers/scsi/scsi_debugfs.c

···
+#include <linux/seq_file.h>
+#include <scsi/scsi_cmnd.h>
+#include <scsi/scsi_dbg.h>
+#include "scsi_debugfs.h"
+
+void scsi_show_rq(struct seq_file *m, struct request *rq)
+{
+	struct scsi_cmnd *cmd = container_of(scsi_req(rq), typeof(*cmd), req);
+	char buf[80];
+
+	__scsi_format_command(buf, sizeof(buf), cmd->cmnd, cmd->cmd_len);
+	seq_printf(m, ", .cmd=%s", buf);
+}

drivers/scsi/scsi_debugfs.h

···
+struct request;
+struct seq_file;
+
+void scsi_show_rq(struct seq_file *m, struct request *rq);

drivers/scsi/scsi_lib.c

···
 
 #include <trace/events/scsi.h>
 
+#include "scsi_debugfs.h"
 #include "scsi_priv.h"
 #include "scsi_logging.h"
 
···
 	.queue_rq	= scsi_queue_rq,
 	.complete	= scsi_softirq_done,
 	.timeout	= scsi_timeout,
+#ifdef CONFIG_BLK_DEBUG_FS
+	.show_rq	= scsi_show_rq,
+#endif
 	.init_request	= scsi_init_request,
 	.exit_request	= scsi_exit_request,
 	.map_queues	= scsi_map_queues,