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block: remove legacy rq tagging

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It's now unused, kill it.

Reviewed-by: Hannes Reinecke <[email protected]>
Tested-by: Ming Lei <[email protected]>
Reviewed-by: Omar Sandoval <[email protected]>
Signed-off-by: Jens Axboe <[email protected]>
This commit is contained in:
Jens Axboe 2018-10-24 03:39:36 -06:00
commit 7ca0192646
8 changed files with 3 additions and 517 deletions
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88
Documentation/block/biodoc.txt
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@ -65,7 +65,6 @@ Description of Contents:
3.2.3 I/O completion
3.2.4 Implications for drivers that do not interpret bios (don't handle
multiple segments)
3.2.5 Request command tagging
3.3 I/O submission
4. The I/O scheduler
5. Scalability related changes
@ -708,93 +707,6 @@ is crossed on completion of a transfer. (The end*request* functions should
be used if only if the request has come down from block/bio path, not for
direct access requests which only specify rq->buffer without a valid rq->bio)
3.2.5 Generic request command tagging
3.2.5.1 Tag helpers
Block now offers some simple generic functionality to help support command
queueing (typically known as tagged command queueing), ie manage more than
one outstanding command on a queue at any given time.
blk_queue_init_tags(struct request_queue *q, int depth)
Initialize internal command tagging structures for a maximum
depth of 'depth'.
blk_queue_free_tags((struct request_queue *q)
Teardown tag info associated with the queue. This will be done
automatically by block if blk_queue_cleanup() is called on a queue
that is using tagging.
The above are initialization and exit management, the main helpers during
normal operations are:
blk_queue_start_tag(struct request_queue *q, struct request *rq)
Start tagged operation for this request. A free tag number between
0 and 'depth' is assigned to the request (rq->tag holds this number),
and 'rq' is added to the internal tag management. If the maximum depth
for this queue is already achieved (or if the tag wasn't started for
some other reason), 1 is returned. Otherwise 0 is returned.
blk_queue_end_tag(struct request_queue *q, struct request *rq)
End tagged operation on this request. 'rq' is removed from the internal
book keeping structures.
To minimize struct request and queue overhead, the tag helpers utilize some
of the same request members that are used for normal request queue management.
This means that a request cannot both be an active tag and be on the queue
list at the same time. blk_queue_start_tag() will remove the request, but
the driver must remember to call blk_queue_end_tag() before signalling
completion of the request to the block layer. This means ending tag
operations before calling end_that_request_last()! For an example of a user
of these helpers, see the IDE tagged command queueing support.
3.2.5.2 Tag info
Some block functions exist to query current tag status or to go from a
tag number to the associated request. These are, in no particular order:
blk_queue_tagged(q)
Returns 1 if the queue 'q' is using tagging, 0 if not.
blk_queue_tag_request(q, tag)
Returns a pointer to the request associated with tag 'tag'.
blk_queue_tag_depth(q)
Return current queue depth.
blk_queue_tag_queue(q)
Returns 1 if the queue can accept a new queued command, 0 if we are
at the maximum depth already.
blk_queue_rq_tagged(rq)
Returns 1 if the request 'rq' is tagged.
3.2.5.2 Internal structure
Internally, block manages tags in the blk_queue_tag structure:
struct blk_queue_tag {
struct request **tag_index; /* array or pointers to rq */
unsigned long *tag_map; /* bitmap of free tags */
struct list_head busy_list; /* fifo list of busy tags */
int busy; /* queue depth */
int max_depth; /* max queue depth */
};
Most of the above is simple and straight forward, however busy_list may need
a bit of explaining. Normally we don't care too much about request ordering,
but in the event of any barrier requests in the tag queue we need to ensure
that requests are restarted in the order they were queue.
3.3 I/O Submission
The routine submit_bio() is used to submit a single io. Higher level i/o