scatterlist: introduce sg_nents_for_len

[karo-tx-linux.git] / lib / scatterlist.c

diff --git a/lib/scatterlist.c b/lib/scatterlist.c
index c9f2e8c6ccc996c8a40bac6872749185170ec7f9..99fbc2f238c4976a1b95df715d22d35f739b4cc7 100644 (file)
--- a/lib/scatterlist.c
+++ b/lib/scatterlist.c
@@ -56,6 +56,38 @@ int sg_nents(struct scatterlist *sg)
 }
 EXPORT_SYMBOL(sg_nents);
 
+/**
+ * sg_nents_for_len - return total count of entries in scatterlist
+ *                    needed to satisfy the supplied length
+ * @sg:                The scatterlist
+ * @len:       The total required length
+ *
+ * Description:
+ * Determines the number of entries in sg that are required to meet
+ * the supplied length, taking into acount chaining as well
+ *
+ * Returns:
+ *   the number of sg entries needed, negative error on failure
+ *
+ **/
+int sg_nents_for_len(struct scatterlist *sg, u64 len)
+{
+       int nents;
+       u64 total;
+
+       if (!len)
+               return 0;
+
+       for (nents = 0, total = 0; sg; sg = sg_next(sg)) {
+               nents++;
+               total += sg->length;
+               if (total >= len)
+                       return nents;
+       }
+
+       return -EINVAL;
+}
+EXPORT_SYMBOL(sg_nents_for_len);
 
 /**
  * sg_last - return the last scatterlist entry in a list