Hi Jens,
On 5/10/07, Jens Axboe <[email protected]> wrote:
The core of the patch - allow the last sg element in a scatterlist
table to point to the start of a new table. We overload the LSB of
the page pointer to indicate whether this is a valid sg entry, or
merely a link to the next list.
Signed-off-by: Jens Axboe <[email protected]>
---
include/asm-i386/scatterlist.h | 2 +
include/linux/scatterlist.h | 52 ++++++++++++++++++++++++++++++++++++++-
2 files changed, 52 insertions(+), 2 deletions(-)
diff --git a/include/asm-i386/scatterlist.h b/include/asm-i386/scatterlist.h
index d7e45a8..bd5164a 100644
--- a/include/asm-i386/scatterlist.h
+++ b/include/asm-i386/scatterlist.h
@@ -10,6 +10,8 @@ struct scatterlist {
unsigned int length;
};
+#define ARCH_HAS_SG_CHAIN
+
/* These macros should be used after a pci_map_sg call has been done
* to get bus addresses of each of the SG entries and their lengths.
* You should only work with the number of sg entries pci_map_sg
diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h
index bed5ab4..fa2dc1c 100644
--- a/include/linux/scatterlist.h
+++ b/include/linux/scatterlist.h
[...]
+/*
+ * We could improve this by passing in the maximum size of an sglist, so
+ * we could jump directly to the last table. That would eliminate this
+ * (potentially) lengthy scan.
+ */
+static inline struct scatterlist *sg_last(struct scatterlist *sgl,
+ unsigned int nents)
+{
+#ifdef 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;
+}
+
+/*
+ * Chain previous sglist to this one
+ */
+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 */
(Style triviality)
In include/linux/scatterlist.h, why not simply:
#ifdef ARCH_HAS_SG_CHAIN
+/*
+ * We could improve this by passing in the maximum size of an sglist, so
+ * we could jump directly to the last table. That would eliminate this
+ * (potentially) lengthy scan.
+ */
+static inline struct scatterlist *sg_last(struct scatterlist *sgl,
+ unsigned int nents)
+{
+ struct scatterlist *ret = &sgl[nents - 1];
+ return ret;
+}
+
+/*
+ * Chain previous sglist to this one
+ */
+static inline void sg_chain(struct scatterlist *prv, unsigned int prv_nents,
+ struct scatterlist *sgl)
+{
+ prv[prv_nents - 1].page = (struct page *) ((unsigned long) sgl | 0x01);
+}
#else
+/*
+ * We could improve this by passing in the maximum size of an sglist, so
+ * we could jump directly to the last table. That would eliminate this
+ * (potentially) lengthy scan.
+ */
+static inline struct scatterlist *sg_last(struct scatterlist *sgl,
+ unsigned int nents)
+{
+ struct scatterlist *sg, *ret = NULL;
+ int i;
+
+ for_each_sg(sgl, sg, nents, i)
+ ret = sg;
+
+ return ret;
+}
+
+/*
+ * Chain previous sglist to this one
+ */
+static inline void sg_chain(struct scatterlist *prv, unsigned int prv_nents,
+ struct scatterlist *sgl)
+{
+ BUG();
+}
#endif /* ARCH_HAS_SG_CHAIN */
Similar to most of the other headers I've seen, and avoids multiple
usage if #ifdef / #ifndef.
-
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