Jeremy Linton wrote:
akpm@xxxxxxxxxxxxxxxxxxxx wrote:
From: Jeremy Linton <jli@xxxxxxxxxxxxxxxxxx>
Any function which use scsi_execute_async() and transfers "odd" sized
data
that doesn't align correctly with the segment sizes may have its transfer
length padded out to the closest segment size.
I would like to strongly suggest that Mike Christie's patch be used
instead.
http://www.mail-archive.com/linux-scsi@xxxxxxxxxxxxxxx/msg06032.html
I finally hit the case he was talking about (the block layer retries 0
length commands caused by a size mismatch) and its ugly. I'm not really
sure why my initial tests weren't hitting that case, I was trying to
understand why some blocks were getting an extra command generated while
others weren't. Sufficient to say, his patch fixes both problems, the
incorrect transfer lengths and the extra 0 length transfer being generated.
I am having trouble inlining the patch properly with my mailer. Here is
the patch from that thread attached if James or Andrew needs it.
sg's may have setup a the buffer with a different length than
the transfer length so we should be using the bufflen passed
in as the request's data len.
Signed-off-by: Mike Christie <michaelc@xxxxxxxxxxx>
diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index 5f95570..30ae831 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -301,7 +301,7 @@ static int scsi_req_map_sg(struct reques
{
struct request_queue *q = rq->q;
int nr_pages = (bufflen + sgl[0].offset + PAGE_SIZE - 1) >> PAGE_SHIFT;
- unsigned int data_len = 0, len, bytes, off;
+ unsigned int data_len = bufflen, len, bytes, off;
struct page *page;
struct bio *bio = NULL;
int i, err, nr_vecs = 0;
@@ -310,10 +310,15 @@ static int scsi_req_map_sg(struct reques
page = sgl[i].page;
off = sgl[i].offset;
len = sgl[i].length;
- data_len += len;
- while (len > 0) {
+ while (len > 0 && data_len > 0) {
+ /*
+ * sg sends a scatterlist that is larger than
+ * the data_len it wants transferred for certain
+ * IO sizes
+ */
bytes = min_t(unsigned int, len, PAGE_SIZE - off);
+ bytes = min(bytes, data_len);
if (!bio) {
nr_vecs = min_t(int, BIO_MAX_PAGES, nr_pages);
@@ -345,12 +350,13 @@ static int scsi_req_map_sg(struct reques
page++;
len -= bytes;
+ data_len -=bytes;
off = 0;
}
}
rq->buffer = rq->data = NULL;
- rq->data_len = data_len;
+ rq->data_len = bufflen;
return 0;
free_bios:
