Merge git://git.kernel.org/pub/scm/linux/kernel/git/sfrench/cifs-2.6

[linux-2.6] / include / linux / scatterlist.h

diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h
index 66ff545552f71ebe11a9cefc373d98fdeedbf321..2dc7464cce5245a0a41e458567372e9401bd58d3 100644 (file)
--- a/include/linux/scatterlist.h
+++ b/include/linux/scatterlist.h
@@ -5,7 +5,7 @@
 #include <linux/mm.h>
 #include <linux/string.h>
 
-static inline void sg_set_buf(struct scatterlist *sg, void *buf,
+static inline void sg_set_buf(struct scatterlist *sg, const void *buf,
                              unsigned int buflen)
 {
        sg->page = virt_to_page(buf);
@@ -13,11 +13,95 @@ static inline void sg_set_buf(struct scatterlist *sg, void *buf,
        sg->length = buflen;
 }
 
-static inline void sg_init_one(struct scatterlist *sg, void *buf,
+static inline void sg_init_one(struct scatterlist *sg, const void *buf,
                               unsigned int buflen)
 {
        memset(sg, 0, sizeof(*sg));
        sg_set_buf(sg, buf, buflen);
 }
 
+/*
+ * We overload the LSB of the page pointer to indicate whether it's
+ * a valid sg entry, or whether it points to the start of a new scatterlist.
+ * Those low bits are there for everyone! (thanks mason :-)
+ */
+#define sg_is_chain(sg)                ((unsigned long) (sg)->page & 0x01)
+#define sg_chain_ptr(sg)       \
+       ((struct scatterlist *) ((unsigned long) (sg)->page & ~0x01))
+
+/**
+ * sg_next - return the next scatterlist entry in a list
+ * @sg:                The current sg entry
+ *
+ * Usually the next entry will be @sg@ + 1, but if this sg element is part
+ * of a chained scatterlist, it could jump to the start of a new
+ * scatterlist array.
+ *
+ * Note that the caller must ensure that there are further entries after
+ * the current entry, this function will NOT return NULL for an end-of-list.
+ *
+ */
+static inline struct scatterlist *sg_next(struct scatterlist *sg)
+{
+       sg++;
+
+       if (unlikely(sg_is_chain(sg)))
+               sg = sg_chain_ptr(sg);
+
+       return sg;
+}
+
+/*
+ * Loop over each sg element, following the pointer to a new list if necessary
+ */
+#define for_each_sg(sglist, sg, nr, __i)       \
+       for (__i = 0, sg = (sglist); __i < (nr); __i++, sg = sg_next(sg))
+
+/**
+ * sg_last - return the last scatterlist entry in a list
+ * @sgl:       First entry in the scatterlist
+ * @nents:     Number of entries in the scatterlist
+ *
+ * Should only be used casually, it (currently) scan the entire list
+ * to get the last entry.
+ *
+ * Note that the @sgl@ pointer passed in need not be the first one,
+ * the important bit is that @nents@ denotes the number of entries that
+ * exist from @sgl@.
+ *
+ */
+static inline struct scatterlist *sg_last(struct scatterlist *sgl,
+                                         unsigned int nents)
+{
+#ifndef ARCH_HAS_SG_CHAIN
+       struct scatterlist *ret = &sgl[nents - 1];
+#else
+       struct scatterlist *sg, *ret = NULL;
+       int i;
+
+       for_each_sg(sgl, sg, nents, i)
+               ret = sg;
+
+#endif
+       return ret;
+}
+
+/**
+ * sg_chain - Chain two sglists together
+ * @prv:       First scatterlist
+ * @prv_nents: Number of entries in prv
+ * @sgl:       Second scatterlist
+ *
+ * Links @prv@ and @sgl@ together, to form a longer scatterlist.
+ *
+ */
+static inline void sg_chain(struct scatterlist *prv, unsigned int prv_nents,
+                           struct scatterlist *sgl)
+{
+#ifndef ARCH_HAS_SG_CHAIN
+       BUG();
+#endif
+       prv[prv_nents - 1].page = (struct page *) ((unsigned long) sgl | 0x01);
+}
+
 #endif /* _LINUX_SCATTERLIST_H */