[PATCH] libata: fix qc->n_elem == 0 case handling in ata_qc_next_sg

This patch makes ata_for_each_sg() start with pad_sgent when
qc->n_elem is zero.  Previously, ata_for_each_sg() unconditionally
started with qc->__sg, handling the first sg to fill_sg() routines
even when the entry was invalid.  And while at it, unwind ?: in
ata_qc_next_sg() into if statement.

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

1 files changed, 14 insertions, 2 deletions

diff --git a/include/linux/libata.h b/include/linux/libata.h
index 9e5db2949c58..c91be5e64ede 100644
--- a/include/linux/libata.h
+++ b/include/linux/libata.h
@@ -557,17 +557,29 @@ ata_sg_is_last(struct scatterlist *sg, struct ata_queued_cmd *qc)
 }
 
 static inline struct scatterlist *
+ata_qc_first_sg(struct ata_queued_cmd *qc)
+{
+        if (qc->n_elem)
+                return qc->__sg;
+        if (qc->pad_len)
+                return &qc->pad_sgent;
+        return NULL;
+}
+
+static inline struct scatterlist *
 ata_qc_next_sg(struct scatterlist *sg, struct ata_queued_cmd *qc)
 {
         if (sg == &qc->pad_sgent)
                 return NULL;
         if (++sg - qc->__sg < qc->n_elem)
                 return sg;
-        return qc->pad_len ? &qc->pad_sgent : NULL;
+        if (qc->pad_len)
+                return &qc->pad_sgent;
+        return NULL;
 }
 
 #define ata_for_each_sg(sg, qc) \
-        for (sg = qc->__sg; sg; sg = ata_qc_next_sg(sg, qc))
+        for (sg = ata_qc_first_sg(qc); sg; sg = ata_qc_next_sg(sg, qc))
 
 static inline unsigned int ata_tag_valid(unsigned int tag)
 {