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SubjectRe: [PATCH 4/4] ide-tape: remove pipeline-specific code from idetape_add_chrdev_read_request()
Date
On Sunday 09 March 2008, Borislav Petkov wrote:
> In order to do away with queueing read requests on the pipeline, several things
> have to be done:
>
> 1. Do not allocate additional pipeline stages in idetape_init_read() until
> (tape->nr_stages < max_stages) and do only read operation preparations. As a
> collateral result, idetape_add_stage_tail() becomes unused so remove it.
>
> 2. Wait for all queued pipeline requests to complete before queueing

Hmm, but we've just removed all pipeline requests with this patch?

[ ->first_stage and ->next_stage are always NULL after this patch which makes
it possible to remove the rest of (now never executed) code for pipeline
support, same for idetape_plug_pipeline() and IDETAPE_FLAG_PIPELINE* flags ]

> the read request's buffer directly thru idetape_queue_rw_tail()
>
> 3. Do next request buffer allocation (tape->merge_stage)

Isn't idetape_init_read() taking care of 3.?

> Signed-off-by: Borislav Petkov <petkovbb@gmail.com>

Seems like we can get away with:

From: Borislav Petkov <petkovbb@googlemail.com>
Subject: [PATCH 4/4] ide-tape: remove pipeline-specific code from idetape_add_chrdev_read_request()

In order to do away with queueing read requests on the pipeline, several things
have to be done:

1. Do not allocate additional pipeline stages in idetape_init_read() until
(tape->nr_stages < max_stages) and do only read operation preparations. As a
collateral result, idetape_add_stage_tail() becomes unused so remove it.

2. Queue the read request's buffer directly thru idetape_queue_rw_tail().

3. Remove now unused idetape_kmalloc_stage() and idetape_switch_buffers().

[bart: simplify the original patch]

Signed-off-by: Borislav Petkov <petkovbb@gmail.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>
---
drivers/ide/ide-tape.c | 96 ++-----------------------------------------------
1 file changed, 5 insertions(+), 91 deletions(-)

Index: b/drivers/ide/ide-tape.c
===================================================================
--- a/drivers/ide/ide-tape.c
+++ b/drivers/ide/ide-tape.c
@@ -1586,15 +1586,6 @@ abort:
return NULL;
}

-static idetape_stage_t *idetape_kmalloc_stage(idetape_tape_t *tape)
-{
- debug_log(DBG_PROCS, "Enter %s\n", __func__);
-
- if (tape->nr_stages >= tape->max_stages)
- return NULL;
- return __idetape_kmalloc_stage(tape, 0, 0);
-}
-
static int idetape_copy_stage_from_user(idetape_tape_t *tape,
idetape_stage_t *stage, const char __user *buf, int n)
{
@@ -1672,39 +1663,6 @@ static void idetape_init_merge_stage(ide
}
}

-static void idetape_switch_buffers(idetape_tape_t *tape, idetape_stage_t *stage)
-{
- struct idetape_bh *tmp;
-
- tmp = stage->bh;
- stage->bh = tape->merge_stage->bh;
- tape->merge_stage->bh = tmp;
- idetape_init_merge_stage(tape);
-}
-
-/* Add a new stage at the end of the pipeline. */
-static void idetape_add_stage_tail(ide_drive_t *drive, idetape_stage_t *stage)
-{
- idetape_tape_t *tape = drive->driver_data;
- unsigned long flags;
-
- debug_log(DBG_PROCS, "Enter %s\n", __func__);
-
- spin_lock_irqsave(&tape->lock, flags);
- stage->next = NULL;
- if (tape->last_stage != NULL)
- tape->last_stage->next = stage;
- else
- tape->first_stage = stage;
- tape->next_stage = stage;
- tape->last_stage = stage;
- if (tape->next_stage == NULL)
- tape->next_stage = tape->last_stage;
- tape->nr_stages++;
- tape->nr_pending_stages++;
- spin_unlock_irqrestore(&tape->lock, flags);
-}
-
/* Install a completion in a pending request and sleep until it is serviced. The
* caller should ensure that the request will not be serviced before we install
* the completion (usually by disabling interrupts).
@@ -2228,10 +2186,7 @@ static void idetape_empty_write_pipeline
static int idetape_init_read(ide_drive_t *drive, int max_stages)
{
idetape_tape_t *tape = drive->driver_data;
- idetape_stage_t *new_stage;
- struct request rq;
int bytes_read;
- u16 blocks = *(u16 *)&tape->caps[12];

/* Initialize read operation */
if (tape->chrdev_dir != IDETAPE_DIR_READ) {
@@ -2267,21 +2222,7 @@ static int idetape_init_read(ide_drive_t
}
}
}
- idetape_init_rq(&rq, REQ_IDETAPE_READ);
- rq.sector = tape->first_frame;
- rq.nr_sectors = blocks;
- rq.current_nr_sectors = blocks;
- if (!test_bit(IDETAPE_FLAG_PIPELINE_ERR, &tape->flags) &&
- tape->nr_stages < max_stages) {
- new_stage = idetape_kmalloc_stage(tape);
- while (new_stage != NULL) {
- new_stage->rq = rq;
- idetape_add_stage_tail(drive, new_stage);
- if (tape->nr_stages >= max_stages)
- break;
- new_stage = idetape_kmalloc_stage(tape);
- }
- }
+
if (!test_bit(IDETAPE_FLAG_PIPELINE_ACTIVE, &tape->flags)) {
if (tape->nr_pending_stages >= 3 * max_stages / 4) {
tape->measure_insert_time = 1;
@@ -2301,9 +2242,6 @@ static int idetape_init_read(ide_drive_t
static int idetape_add_chrdev_read_request(ide_drive_t *drive, int blocks)
{
idetape_tape_t *tape = drive->driver_data;
- unsigned long flags;
- struct request *rq_ptr;
- int bytes_read;

debug_log(DBG_PROCS, "Enter %s, %d blocks\n", __func__, blocks);

@@ -2311,37 +2249,13 @@ static int idetape_add_chrdev_read_reque
if (test_bit(IDETAPE_FLAG_FILEMARK, &tape->flags))
return 0;

- /* Wait for the next block to reach the head of the pipeline. */
idetape_init_read(drive, tape->max_stages);
- if (tape->first_stage == NULL) {
- if (test_bit(IDETAPE_FLAG_PIPELINE_ERR, &tape->flags))
- return 0;
- return idetape_queue_rw_tail(drive, REQ_IDETAPE_READ, blocks,
- tape->merge_stage->bh);
- }
- idetape_wait_first_stage(drive);
- rq_ptr = &tape->first_stage->rq;
- bytes_read = tape->blk_size * (rq_ptr->nr_sectors -
- rq_ptr->current_nr_sectors);
- rq_ptr->nr_sectors = 0;
- rq_ptr->current_nr_sectors = 0;

- if (rq_ptr->errors == IDETAPE_ERROR_EOD)
+ if (test_bit(IDETAPE_FLAG_PIPELINE_ERR, &tape->flags))
return 0;
- else {
- idetape_switch_buffers(tape, tape->first_stage);
- if (rq_ptr->errors == IDETAPE_ERROR_FILEMARK)
- set_bit(IDETAPE_FLAG_FILEMARK, &tape->flags);
- spin_lock_irqsave(&tape->lock, flags);
- idetape_remove_stage_head(drive);
- spin_unlock_irqrestore(&tape->lock, flags);
- }
- if (bytes_read > blocks * tape->blk_size) {
- printk(KERN_ERR "ide-tape: bug: trying to return more bytes"
- " than requested\n");
- bytes_read = blocks * tape->blk_size;
- }
- return (bytes_read);
+
+ return idetape_queue_rw_tail(drive, REQ_IDETAPE_READ, blocks,
+ tape->merge_stage->bh);
}

static void idetape_pad_zeros(ide_drive_t *drive, int bcount)

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