libata: add command iterator helpers

Now that we have the internal tag as a special (higher) value tag,
it gets a bit tricky to iterate the internal commands as some loops
will exceed ATA_MAX_QUEUE. Add explicit helpers for iterating pending
commands, both inflight and internal.
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Tejun Heo <tj@kernel.org>

include/linux/libata.h

@@ -1495,6 +1495,29 @@ static inline bool ata_tag_valid(unsigned int tag)
 	return tag < ATA_MAX_QUEUE || ata_tag_internal(tag);
 }
 
+#define __ata_qc_for_each(ap, qc, tag, max_tag, fn)		\
+	for ((tag) = 0; (tag) < (max_tag) &&			\
+	     ({ qc = fn((ap), (tag)); 1; }); (tag)++)		\
+
+/*
+ * Internal use only, iterate commands ignoring error handling and
+ * status of 'qc'.
+ */
+#define ata_qc_for_each_raw(ap, qc, tag)					\
+	__ata_qc_for_each(ap, qc, tag, ATA_MAX_QUEUE, __ata_qc_from_tag)
+
+/*
+ * Iterate all potential commands that can be queued
+ */
+#define ata_qc_for_each(ap, qc, tag)					\
+	__ata_qc_for_each(ap, qc, tag, ATA_MAX_QUEUE, ata_qc_from_tag)
+
+/*
+ * Like ata_qc_for_each, but with the internal tag included
+ */
+#define ata_qc_for_each_with_internal(ap, qc, tag)			\
+	__ata_qc_for_each(ap, qc, tag, ATA_MAX_QUEUE + 1, ata_qc_from_tag)
+
 /*
  * device helpers
  */