[PATCH] libata: fix WARN_ON() condition in *_fill_sg()

For ATAPI commands, padding can reduce qc->n_elem by one and thus to
zero making assert(qc->n_elem > 0)'s in ata_fill_sg() and qs_fill_sg()
fail for legal commands.  This patch fixes the assert()'s to take
qc->pad_len into account.

Although the condition check seems a bit excessive, as this part of
code isn't still stable yet, I think it's worth to keep those.

Signed-off-by: Tejun Heo <htejun@gmail.com>
Signed-off-by: Jeff Garzik <jgarzik@pobox.com>

drivers/scsi/libata-core.c

@@ -2570,7 +2570,7 @@ static void ata_fill_sg(struct ata_queued_cmd *qc)
 	unsigned int idx;
 
 	assert(qc->__sg != NULL);
-	assert(qc->n_elem > 0);
+	assert(qc->n_elem > 0 || qc->pad_len > 0);
 
 	idx = 0;
 	ata_for_each_sg(sg, qc) {

drivers/scsi/sata_qstor.c

@@ -277,7 +277,7 @@ static unsigned int qs_fill_sg(struct ata_queued_cmd *qc)
 	u8 *prd = pp->pkt + QS_CPB_BYTES;
 
 	assert(qc->__sg != NULL);
-	assert(qc->n_elem > 0);
+	assert(qc->n_elem > 0 || qc->pad_len > 0);
 
 	nelem = 0;
 	ata_for_each_sg(sg, qc) {