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Date: Tue, 04 Mar 2008 18:22:28 +0900
From: FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
To: jens.axboe@...cle.com, htejun@...il.com
Cc: tomof@....org, James.Bottomley@...senPartnership.com,
efault@....de, akpm@...ux-foundation.org,
linux-kernel@...r.kernel.org, linux-ide@...r.kernel.org,
linux-scsi@...r.kernel.org, jgarzik@...ox.com, bzolnier@...il.com
Subject: Re: [PATCH] block: fix residual byte count handling
On Tue, 04 Mar 2008 18:06:48 +0900
FUJITA Tomonori <fujita.tomonori@....ntt.co.jp> wrote:
> On Tue, 4 Mar 2008 09:59:46 +0100
> Jens Axboe <jens.axboe@...cle.com> wrote:
>
> > On Tue, Mar 04 2008, FUJITA Tomonori wrote:
> > > On Tue, 04 Mar 2008 11:32:56 +0900
> > > Tejun Heo <htejun@...il.com> wrote:
> > >
> > > > FUJITA Tomonori wrote:
> > > > >> Yeah, libata did its own padding and needed to add draining. Private
> > > > >> implementation was complex as hell and James suggested moving them to
> > > > >> block layer. Are you suggesting moving them back to drivers?
> > > > >
> > > > > No, I'm not. I've been working on the IOMMUs to remove such
> > > > > workarounds in LLDs.
> > > > >
> > > > > What drivers need to do on this is just adding a padding length, that
> > > > > is, drivers don't need to change the structure of the sg list (like
> > > > > splitting a sg entry), right? And it doesn't break the SAS drivers
> > > > > that support SATAPI, does it?
> > > > >
> > > > > But I agree that drivers want to get a complete sglist so I'm fine
> > > > > with adjusting sglist entries in the block layer with your secode
> > > > > patch (separate out padding from alignment). As we discussed, I'm fine
> > > > > with breaking sum(sg) == rq->data_len as long as rq->data_len means
> > > > > the true data length.
> > > >
> > > > As long as the second patch is in, what value rq->data_len indicates
> > > > doesn't matter to drivers which don't use explicit padding or draining,
> > > > so the situation is much more controlled. I don't care which value
> > > > rq->data_len would indicate. I'd prefer it equal sum(sg) as that value
> > > > is what IDE and libata which will be the major users of padding and/or
> > > > draining expect in rq->data_len but fixing up that shouldn't be too
> > > > difficult. I guess this can be determined by Jens. If Jens likes
> > > > rq->data_len to contain requested transfer size, I'll post updated patches.
> > >
> > > OK, I prefer rq->data_len means the true data length though you prefer
> > > rq->data_len means the allocated buffer length (the true data length
> > > plus padding and drain). We agree on other things. We can live with
> > > either way.
> > >
> > > Jens, what's your preference?
> >
> > I completely agree with you, ->data_len meaning true data length is way
> > cleaner imho. Only the driver should care for the padded length, all
> > other parts of the kernel only need to know what they actually got.
>
> OK, now we can fix the whole SG_IO (and bsg handler) mess.
>
> Here's my patch with a proper description. which several people have
> already tested (thanks!). Then we need an updated version of Tejun's
> separate out padding from alignment patch.
OK, I've updated his patch. Tejun, can you audit this?
Thanks,
=
From: Tejun Heo <htejun@...il.com>
Subject: [PATCH] block: separate out padding from alignment
Block layer alignment was used for two different purposes - memory
alignment and padding. This causes problems in lower layers because
drivers which only require memory alignment ends up with adjusted
rq->data_len. Separate out padding such that padding occurs iff
driver explicitly requests it.
Tomo: restorethe code to update bio in blk_rq_map_user
introduced by the commit 40b01b9bbdf51ae543a04744283bf2d56c4a6afa
according to padding alignment.
Signed-off-by: Tejun Heo <htejun@...il.com>
Signed-off-by: FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
---
block/blk-map.c | 20 +++++++++++++-------
block/blk-settings.c | 17 +++++++++++++++++
drivers/ata/libata-scsi.c | 3 ++-
include/linux/blkdev.h | 2 ++
4 files changed, 34 insertions(+), 8 deletions(-)
diff --git a/block/blk-map.c b/block/blk-map.c
index f559832..4e17dfd 100644
--- a/block/blk-map.c
+++ b/block/blk-map.c
@@ -43,6 +43,7 @@ static int __blk_rq_map_user(struct request_queue *q, struct request *rq,
void __user *ubuf, unsigned int len)
{
unsigned long uaddr;
+ unsigned int alignment;
struct bio *bio, *orig_bio;
int reading, ret;
@@ -53,8 +54,8 @@ static int __blk_rq_map_user(struct request_queue *q, struct request *rq,
* direct dma. else, set up kernel bounce buffers
*/
uaddr = (unsigned long) ubuf;
- if (!(uaddr & queue_dma_alignment(q)) &&
- !(len & queue_dma_alignment(q)))
+ alignment = queue_dma_alignment(q) | q->dma_pad_mask;
+ if (!(uaddr & alignment) && !(len & alignment))
bio = bio_map_user(q, NULL, uaddr, len, reading);
else
bio = bio_copy_user(q, uaddr, len, reading);
@@ -141,15 +142,20 @@ int blk_rq_map_user(struct request_queue *q, struct request *rq,
/*
* __blk_rq_map_user() copies the buffers if starting address
- * or length isn't aligned. As the copied buffer is always
- * page aligned, we know that there's enough room for padding.
- * Extend the last bio and update rq->data_len accordingly.
+ * or length isn't aligned to dma_pad_mask. As the copied
+ * buffer is always page aligned, we know that there's enough
+ * room for padding. Extend the last bio and update
+ * rq->data_len accordingly.
*
* On unmap, bio_uncopy_user() will use unmodified
* bio_map_data pointed to by bio->bi_private.
*/
- if (len & queue_dma_alignment(q)) {
- unsigned int pad_len = (queue_dma_alignment(q) & ~len) + 1;
+ if (len & q->dma_pad_mask) {
+ unsigned int pad_len = (q->dma_pad_mask & ~len) + 1;
+ struct bio *bio = rq->biotail;
+
+ bio->bi_io_vec[bio->bi_vcnt - 1].bv_len += pad_len;
+ bio->bi_size += pad_len;
rq->extra_len += pad_len;
}
diff --git a/block/blk-settings.c b/block/blk-settings.c
index 9a8ffdd..5fcb625 100644
--- a/block/blk-settings.c
+++ b/block/blk-settings.c
@@ -293,6 +293,23 @@ void blk_queue_stack_limits(struct request_queue *t, struct request_queue *b)
EXPORT_SYMBOL(blk_queue_stack_limits);
/**
+ * blk_queue_dma_pad - set pad mask
+ * @q: the request queue for the device
+ * @mask: pad mask
+ *
+ * Set pad mask. Direct IO requests are padded to the mask specified.
+ *
+ * Appending pad buffer to a request modifies ->data_len such that it
+ * includes the pad buffer. The original requested data length can be
+ * obtained using blk_rq_raw_data_len().
+ **/
+void blk_queue_dma_pad(struct request_queue *q, unsigned int mask)
+{
+ q->dma_pad_mask = mask;
+}
+EXPORT_SYMBOL(blk_queue_dma_pad);
+
+/**
* blk_queue_dma_drain - Set up a drain buffer for excess dma.
*
* @q: the request queue for the device
diff --git a/drivers/ata/libata-scsi.c b/drivers/ata/libata-scsi.c
index fe47922..8f0e8f2 100644
--- a/drivers/ata/libata-scsi.c
+++ b/drivers/ata/libata-scsi.c
@@ -862,9 +862,10 @@ static int ata_scsi_dev_config(struct scsi_device *sdev,
struct request_queue *q = sdev->request_queue;
void *buf;
- /* set the min alignment */
+ /* set the min alignment and padding */
blk_queue_update_dma_alignment(sdev->request_queue,
ATA_DMA_PAD_SZ - 1);
+ blk_queue_dma_pad(sdev->request_queue, ATA_DMA_PAD_SZ - 1);
/* configure draining */
buf = kmalloc(ATAPI_MAX_DRAIN, q->bounce_gfp | GFP_KERNEL);
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index b72526c..6f79d40 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -362,6 +362,7 @@ struct request_queue
unsigned long seg_boundary_mask;
void *dma_drain_buffer;
unsigned int dma_drain_size;
+ unsigned int dma_pad_mask;
unsigned int dma_alignment;
struct blk_queue_tag *queue_tags;
@@ -701,6 +702,7 @@ extern void blk_queue_max_hw_segments(struct request_queue *, unsigned short);
extern void blk_queue_max_segment_size(struct request_queue *, unsigned int);
extern void blk_queue_hardsect_size(struct request_queue *, unsigned short);
extern void blk_queue_stack_limits(struct request_queue *t, struct request_queue *b);
+extern void blk_queue_dma_pad(struct request_queue *, unsigned int);
extern int blk_queue_dma_drain(struct request_queue *q,
dma_drain_needed_fn *dma_drain_needed,
void *buf, unsigned int size);
--
1.5.3.6
--
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