[PATCH] [SCSI] sg.c: SG_DXFER_TO_FROM_DEV mean DMA_BIDIRECTIONAL

[PATCH] [SCSI] sg.c: SG_DXFER_TO_FROM_DEV mean DMA_BIDIRECTIONAL

[Luben Tuikov]

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SG_DXFER_TO_FROM_DEV means DMA_BIDIRECTIONAL, not
DMA_FROM_DEVICE.

Signed-off-by: Luben Tuikov <ltuikov@yahoo.com>
---
 drivers/scsi/sg.c |   11 +++++------
 1 files changed, 5 insertions(+), 6 deletions(-)

This patch is 8 months old.

     Luben

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diff --git a/drivers/scsi/sg.c b/drivers/scsi/sg.c
index 5a0a193..3f81477 100644
--- a/drivers/scsi/sg.c
+++ b/drivers/scsi/sg.c
@@ -608,12 +608,11 @@ sg_write(struct file *filp, const char _
 	if (hp->dxfer_direction == SG_DXFER_TO_FROM_DEV)
 		if (printk_ratelimit())
 			printk(KERN_WARNING
-			       "sg_write: data in/out %d/%d bytes for SCSI command 0x%x--"
-			       "guessing data in;\n" KERN_WARNING "   "
-			       "program %s not setting count and/or reply_len properly\n",
+			       "sg_write: program %s: data in/out %d/%d bytes for SCSI command 0x%x--"
+			       "bidirectional;\n",
+			       current->comm,
 			       old_hdr.reply_len - (int)SZ_SG_HEADER,
-			       input_size, (unsigned int) cmnd[0],
-			       current->comm);
+			       input_size, (unsigned int) cmnd[0]);
 	k = sg_common_write(sfp, srp, cmnd, sfp->timeout, blocking);
 	return (k < 0) ? k : count;
 }
@@ -724,13 +723,13 @@ sg_common_write(Sg_fd * sfp, Sg_request
 	}
 
 	switch (hp->dxfer_direction) {
-	case SG_DXFER_TO_FROM_DEV:
 	case SG_DXFER_FROM_DEV:
 		data_dir = DMA_FROM_DEVICE;
 		break;
 	case SG_DXFER_TO_DEV:
 		data_dir = DMA_TO_DEVICE;
 		break;
+	case SG_DXFER_TO_FROM_DEV:
 	case SG_DXFER_UNKNOWN:
 		data_dir = DMA_BIDIRECTIONAL;
 		break;
-- 
1.4.3.3.g8478

Re: [PATCH] [SCSI] sg.c: SG_DXFER_TO_FROM_DEV mean DMA_BIDIRECTIONAL

[Jeff Garzik]

Luben Tuikov wrote:
> SG_DXFER_TO_FROM_DEV means DMA_BIDIRECTIONAL, not
> DMA_FROM_DEVICE.
> 
> Signed-off-by: Luben Tuikov <ltuikov@yahoo.com>

ACK

Re: [PATCH] [SCSI] sg.c: SG_DXFER_TO_FROM_DEV mean DMA_BIDIRECTIONAL

[Douglas Gilbert]

Luben Tuikov wrote:
> SG_DXFER_TO_FROM_DEV means DMA_BIDIRECTIONAL, not
> DMA_FROM_DEVICE.
> 
> Signed-off-by: Luben Tuikov <ltuikov@yahoo.com>
> ---
>  drivers/scsi/sg.c |   11 +++++------
>  1 files changed, 5 insertions(+), 6 deletions(-)
> 
> This patch is 8 months old.

While this patch is sensible, it breaks a very arcane
usage that I inherited with the sg driver in 1998.
At that time there was no resid, so application clients
(e.g. cdrecord) had no way of knowing if the amount of
data they requested to be read, was actually read.
So, as indirect IO was the only game in town, the
hack used was to prefill the kernel buffer prior to
a read, and then check if it had been overwritten
after the read operation.
Hence SG_DXFER_TO_FROM_DEV was actually a read from
the device.

Some LLDs still do not implement resid (properly).

I'm happy to accept the change as long as people are
prepared to wear the breakage.

Doug Gilbert

Re: [PATCH] [SCSI] sg.c: SG_DXFER_TO_FROM_DEV mean DMA_BIDIRECTIONAL

[James Bottomley]

On Sun, 2006-11-05 at 09:34 -0500, Douglas Gilbert wrote:
> I'm happy to accept the change as long as people are
> prepared to wear the breakage.

You're the maintainer ... is that an ACK or a NACK?

James