1 files changed, 209 insertions, 0 deletions
diff --git a/sys/geom/sched/subr_disk.c b/sys/geom/sched/subr_disk.c
new file mode 100644
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--- /dev/null
+++ b/sys/geom/sched/subr_disk.c
@@ -0,0 +1,209 @@
+/*-
+ * ----------------------------------------------------------------------------
+ * "THE BEER-WARE LICENSE" (Revision 42):
+ * <phk@FreeBSD.ORG> wrote this file.  As long as you retain this notice you
+ * can do whatever you want with this stuff. If we meet some day, and you think
+ * this stuff is worth it, you can buy me a beer in return.   Poul-Henning Kamp
+ * ----------------------------------------------------------------------------
+ *
+ * The bioq_disksort() (and the specification of the bioq API)
+ * have been written by Luigi Rizzo and Fabio Checconi under the same
+ * license as above.
+ */
+
+#include <sys/cdefs.h>
+__FBSDID("$FreeBSD$");
+
+//#include "opt_geom.h"
+
+#include <sys/param.h>
+#include <sys/systm.h>
+#include <sys/bio.h>
+#include <sys/conf.h>
+#include <sys/disk.h>
+#include <geom/geom_disk.h>
+#include "g_sched.h"
+
+/*
+ * BIO queue implementation
+ *
+ * Please read carefully the description below before making any change
+ * to the code, or you might change the behaviour of the data structure
+ * in undesirable ways.
+ *
+ * A bioq stores disk I/O request (bio), normally sorted according to
+ * the distance of the requested position (bio->bio_offset) from the
+ * current head position (bioq->last_offset) in the scan direction, i.e.
+ *
+ * 	(uoff_t)(bio_offset - last_offset)
+ *
+ * Note that the cast to unsigned (uoff_t) is fundamental to insure
+ * that the distance is computed in the scan direction.
+ *
+ * The main methods for manipulating the bioq are:
+ *
+ *   bioq_disksort()	performs an ordered insertion;
+ *
+ *   bioq_first()	return the head of the queue, without removing;
+ *
+ *   bioq_takefirst()	return and remove the head of the queue,
+ *		updating the 'current head position' as
+ *		bioq->last_offset = bio->bio_offset + bio->bio_length;
+ *
+ * When updating the 'current head position', we assume that the result of
+ * bioq_takefirst() is dispatched to the device, so bioq->last_offset
+ * represents the head position once the request is complete.
+ *
+ * If the bioq is manipulated using only the above calls, it starts
+ * with a sorted sequence of requests with bio_offset >= last_offset,
+ * possibly followed by another sorted sequence of requests with
+ * 0 <= bio_offset < bioq->last_offset 
+ *
+ * NOTE: historical behaviour was to ignore bio->bio_length in the
+ *	update, but its use tracks the head position in a better way.
+ *	Historical behaviour was also to update the head position when
+ *	the request under service is complete, rather than when the
+ *	request is extracted from the queue. However, the current API
+ *	has no method to update the head position; secondly, once
+ *	a request has been submitted to the disk, we have no idea of
+ *	the actual head position, so the final one is our best guess.
+ *
+ * --- Direct queue manipulation ---
+ *
+ * A bioq uses an underlying TAILQ to store requests, so we also
+ * export methods to manipulate the TAILQ, in particular:
+ *
+ * bioq_insert_tail()	insert an entry at the end.
+ *		It also creates a 'barrier' so all subsequent
+ *		insertions through bioq_disksort() will end up
+ *		after this entry;
+ *
+ * bioq_insert_head()	insert an entry at the head, update
+ *		bioq->last_offset = bio->bio_offset so that
+ *		all subsequent insertions through bioq_disksort()
+ *		will end up after this entry;
+ *
+ * bioq_remove()	remove a generic element from the queue, act as
+ *		bioq_takefirst() if invoked on the head of the queue.
+ *
+ * The semantic of these methods is the same of the operations
+ * on the underlying TAILQ, but with additional guarantees on
+ * subsequent bioq_disksort() calls. E.g. bioq_insert_tail()
+ * can be useful for making sure that all previous ops are flushed
+ * to disk before continuing.
+ *
+ * Updating bioq->last_offset on a bioq_insert_head() guarantees
+ * that the bio inserted with the last bioq_insert_head() will stay
+ * at the head of the queue even after subsequent bioq_disksort().
+ *
+ * Note that when the direct queue manipulation functions are used,
+ * the queue may contain multiple inversion points (i.e. more than
+ * two sorted sequences of requests).
+ *
+ */
+
+void
+gs_bioq_init(struct bio_queue_head *head)
+{
+
+	TAILQ_INIT(&head->queue);
+	head->last_offset = 0;
+	head->insert_point = NULL;
+}
+
+void
+gs_bioq_remove(struct bio_queue_head *head, struct bio *bp)
+{
+
+	if (bp == TAILQ_FIRST(&head->queue))
+		head->last_offset = bp->bio_offset + bp->bio_length;
+
+	if (bp == head->insert_point)
+		head->insert_point = NULL;
+
+	TAILQ_REMOVE(&head->queue, bp, bio_queue);
+}
+
+void
+gs_bioq_flush(struct bio_queue_head *head, struct devstat *stp, int error)
+{
+	struct bio *bp;
+
+	while ((bp = gs_bioq_takefirst(head)) != NULL)
+		biofinish(bp, stp, error);
+}
+
+void
+gs_bioq_insert_head(struct bio_queue_head *head, struct bio *bp)
+{
+
+	head->last_offset = bp->bio_offset;
+	TAILQ_INSERT_HEAD(&head->queue, bp, bio_queue);
+}
+
+void
+gs_bioq_insert_tail(struct bio_queue_head *head, struct bio *bp)
+{
+
+	TAILQ_INSERT_TAIL(&head->queue, bp, bio_queue);
+	head->insert_point = bp;
+}
+
+struct bio *
+gs_bioq_first(struct bio_queue_head *head)
+{
+
+	return (TAILQ_FIRST(&head->queue));
+}
+
+struct bio *
+gs_bioq_takefirst(struct bio_queue_head *head)
+{
+	struct bio *bp;
+
+	bp = TAILQ_FIRST(&head->queue);
+	if (bp != NULL)
+		gs_bioq_remove(head, bp);
+	return (bp);
+}
+
+/*
+ * Compute the sorting key. The cast to unsigned is
+ * fundamental for correctness, see the description
+ * near the beginning of the file.
+ */
+static inline uoff_t
+gs_bioq_bio_key(struct bio_queue_head *head, struct bio *bp)
+{
+
+	return ((uoff_t)(bp->bio_offset - head->last_offset));
+}
+
+/*
+ * Seek sort for disks.
+ *
+ * Sort all requests in a single queue while keeping
+ * track of the current position of the disk with last_offset.
+ * See above for details.
+ */
+void
+gs_bioq_disksort(struct bio_queue_head *head, struct bio *bp)
+{
+	struct bio *cur, *prev = NULL;
+	uoff_t key = gs_bioq_bio_key(head, bp);
+
+	cur = TAILQ_FIRST(&head->queue);
+
+	if (head->insert_point)
+		cur = head->insert_point;
+
+	while (cur != NULL && key >= gs_bioq_bio_key(head, cur)) {
+		prev = cur;
+		cur = TAILQ_NEXT(cur, bio_queue);
+	}
+
+	if (prev == NULL)
+		TAILQ_INSERT_HEAD(&head->queue, bp, bio_queue);
+	else
+		TAILQ_INSERT_AFTER(&head->queue, prev, bp, bio_queue);
+}