[PATCH v10 04/18] scsi: core: Introduce a mechanism for reordering requests in the error handler

[Bart Van Assche <bvanassche@acm.org>]

Introduce the .eh_needs_prepare_resubmit and the .eh_prepare_resubmit
function pointers in struct scsi_driver. Make the error handler call
.eh_prepare_resubmit() before resubmitting commands if any of the
.eh_needs_prepare_resubmit() invocations return true. A later patch
will use this functionality to sort SCSI commands by LBA from inside
the SCSI disk driver before these are resubmitted by the error handler.

Cc: Martin K. Petersen <martin.petersen@oracle.com>
Cc: Damien Le Moal <dlemoal@kernel.org>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
---
 drivers/scsi/scsi_error.c  | 65 ++++++++++++++++++++++++++++++++++++++
 drivers/scsi/scsi_priv.h   |  1 +
 include/scsi/scsi_driver.h |  2 ++
 3 files changed, 68 insertions(+)

diff --git a/drivers/scsi/scsi_error.c b/drivers/scsi/scsi_error.c
index c67cdcdc3ba8..c4d817f044a0 100644
--- a/drivers/scsi/scsi_error.c
+++ b/drivers/scsi/scsi_error.c
@@ -27,6 +27,7 @@
 #include <linux/blkdev.h>
 #include <linux/delay.h>
 #include <linux/jiffies.h>
+#include <linux/list_sort.h>
 
 #include <scsi/scsi.h>
 #include <scsi/scsi_cmnd.h>
@@ -2186,6 +2187,68 @@ void scsi_eh_ready_devs(struct Scsi_Host *shost,
 }
 EXPORT_SYMBOL_GPL(scsi_eh_ready_devs);
 
+/*
+ * Returns true if .eh_prepare_resubmit should be called for the commands in
+ * @done_q.
+ */
+static bool scsi_needs_preparation(struct list_head *done_q)
+{
+	struct scsi_cmnd *scmd;
+
+	list_for_each_entry(scmd, done_q, eh_entry) {
+		struct scsi_driver *uld = scsi_cmd_to_driver(scmd);
+		bool (*npr)(struct scsi_cmnd *) = uld->eh_needs_prepare_resubmit;
+
+		if (npr && npr(scmd))
+			return true;
+	}
+
+	return false;
+}
+
+/*
+ * Comparison function that allows to sort SCSI commands by ULD driver.
+ */
+static int scsi_cmp_uld(void *priv, const struct list_head *_a,
+			const struct list_head *_b)
+{
+	struct scsi_cmnd *a = list_entry(_a, typeof(*a), eh_entry);
+	struct scsi_cmnd *b = list_entry(_b, typeof(*b), eh_entry);
+
+	/* See also the comment above the list_sort() definition. */
+	return scsi_cmd_to_driver(a) > scsi_cmd_to_driver(b);
+}
+
+void scsi_call_prepare_resubmit(struct list_head *done_q)
+{
+	struct scsi_cmnd *scmd, *next;
+
+	if (!scsi_needs_preparation(done_q))
+		return;
+
+	/* Sort pending SCSI commands by ULD. */
+	list_sort(NULL, done_q, scsi_cmp_uld);
+
+	/*
+	 * Call .eh_prepare_resubmit for each range of commands with identical
+	 * ULD driver pointer.
+	 */
+	list_for_each_entry_safe(scmd, next, done_q, eh_entry) {
+		struct scsi_driver *uld = scsi_cmd_to_driver(scmd);
+		struct list_head *prev, uld_cmd_list;
+
+		while (&next->eh_entry != done_q &&
+		       scsi_cmd_to_driver(next) == uld)
+			next = list_next_entry(next, eh_entry);
+		if (!uld->eh_prepare_resubmit)
+			continue;
+		prev = scmd->eh_entry.prev;
+		list_cut_position(&uld_cmd_list, prev, next->eh_entry.prev);
+		uld->eh_prepare_resubmit(&uld_cmd_list);
+		list_splice(&uld_cmd_list, prev);
+	}
+}
+
 /**
  * scsi_eh_flush_done_q - finish processed commands or retry them.
  * @done_q:	list_head of processed commands.
@@ -2194,6 +2257,8 @@ void scsi_eh_flush_done_q(struct list_head *done_q)
 {
 	struct scsi_cmnd *scmd, *next;
 
+	scsi_call_prepare_resubmit(done_q);
+
 	list_for_each_entry_safe(scmd, next, done_q, eh_entry) {
 		list_del_init(&scmd->eh_entry);
 		if (scsi_device_online(scmd->device) &&
diff --git a/drivers/scsi/scsi_priv.h b/drivers/scsi/scsi_priv.h
index f42388ecb024..df4af4645430 100644
--- a/drivers/scsi/scsi_priv.h
+++ b/drivers/scsi/scsi_priv.h
@@ -101,6 +101,7 @@ int scsi_eh_get_sense(struct list_head *work_q,
 		      struct list_head *done_q);
 bool scsi_noretry_cmd(struct scsi_cmnd *scmd);
 void scsi_eh_done(struct scsi_cmnd *scmd);
+void scsi_call_prepare_resubmit(struct list_head *done_q);
 
 /* scsi_lib.c */
 extern int scsi_maybe_unblock_host(struct scsi_device *sdev);
diff --git a/include/scsi/scsi_driver.h b/include/scsi/scsi_driver.h
index 4ce1988b2ba0..00ffa470724a 100644
--- a/include/scsi/scsi_driver.h
+++ b/include/scsi/scsi_driver.h
@@ -18,6 +18,8 @@ struct scsi_driver {
 	int (*done)(struct scsi_cmnd *);
 	int (*eh_action)(struct scsi_cmnd *, int);
 	void (*eh_reset)(struct scsi_cmnd *);
+	bool (*eh_needs_prepare_resubmit)(struct scsi_cmnd *cmd);
+	void (*eh_prepare_resubmit)(struct list_head *cmd_list);
 };
 #define to_scsi_driver(drv) \
 	container_of((drv), struct scsi_driver, gendrv)