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-rw-r--r--include/linux/scatterlist.h38
-rw-r--r--lib/scatterlist.c176
2 files changed, 168 insertions, 46 deletions
diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h
index 71fc81360048..e5996984ddd0 100644
--- a/include/linux/scatterlist.h
+++ b/include/linux/scatterlist.h
@@ -224,4 +224,42 @@ size_t sg_copy_to_buffer(struct scatterlist *sgl, unsigned int nents,
*/
#define SG_MAX_SINGLE_ALLOC (PAGE_SIZE / sizeof(struct scatterlist))
+
+/*
+ * Mapping sg iterator
+ *
+ * Iterates over sg entries mapping page-by-page. On each successful
+ * iteration, @miter->page points to the mapped page and
+ * @miter->length bytes of data can be accessed at @miter->addr. As
+ * long as an interation is enclosed between start and stop, the user
+ * is free to choose control structure and when to stop.
+ *
+ * @miter->consumed is set to @miter->length on each iteration. It
+ * can be adjusted if the user can't consume all the bytes in one go.
+ * Also, a stopped iteration can be resumed by calling next on it.
+ * This is useful when iteration needs to release all resources and
+ * continue later (e.g. at the next interrupt).
+ */
+
+#define SG_MITER_ATOMIC (1 << 0) /* use kmap_atomic */
+
+struct sg_mapping_iter {
+ /* the following three fields can be accessed directly */
+ struct page *page; /* currently mapped page */
+ void *addr; /* pointer to the mapped area */
+ size_t length; /* length of the mapped area */
+ size_t consumed; /* number of consumed bytes */
+
+ /* these are internal states, keep away */
+ struct scatterlist *__sg; /* current entry */
+ unsigned int __nents; /* nr of remaining entries */
+ unsigned int __offset; /* offset within sg */
+ unsigned int __flags;
+};
+
+void sg_miter_start(struct sg_mapping_iter *miter, struct scatterlist *sgl,
+ unsigned int nents, unsigned int flags);
+bool sg_miter_next(struct sg_mapping_iter *miter);
+void sg_miter_stop(struct sg_mapping_iter *miter);
+
#endif /* _LINUX_SCATTERLIST_H */
diff --git a/lib/scatterlist.c b/lib/scatterlist.c
index b80c21100d78..876ba6d5b670 100644
--- a/lib/scatterlist.c
+++ b/lib/scatterlist.c
@@ -295,6 +295,117 @@ int sg_alloc_table(struct sg_table *table, unsigned int nents, gfp_t gfp_mask)
EXPORT_SYMBOL(sg_alloc_table);
/**
+ * sg_miter_start - start mapping iteration over a sg list
+ * @miter: sg mapping iter to be started
+ * @sgl: sg list to iterate over
+ * @nents: number of sg entries
+ *
+ * Description:
+ * Starts mapping iterator @miter.
+ *
+ * Context:
+ * Don't care.
+ */
+void sg_miter_start(struct sg_mapping_iter *miter, struct scatterlist *sgl,
+ unsigned int nents, unsigned int flags)
+{
+ memset(miter, 0, sizeof(struct sg_mapping_iter));
+
+ miter->__sg = sgl;
+ miter->__nents = nents;
+ miter->__offset = 0;
+ miter->__flags = flags;
+}
+EXPORT_SYMBOL(sg_miter_start);
+
+/**
+ * sg_miter_next - proceed mapping iterator to the next mapping
+ * @miter: sg mapping iter to proceed
+ *
+ * Description:
+ * Proceeds @miter@ to the next mapping. @miter@ should have been
+ * started using sg_miter_start(). On successful return,
+ * @miter@->page, @miter@->addr and @miter@->length point to the
+ * current mapping.
+ *
+ * Context:
+ * IRQ disabled if SG_MITER_ATOMIC. IRQ must stay disabled till
+ * @miter@ is stopped. May sleep if !SG_MITER_ATOMIC.
+ *
+ * Returns:
+ * true if @miter contains the next mapping. false if end of sg
+ * list is reached.
+ */
+bool sg_miter_next(struct sg_mapping_iter *miter)
+{
+ unsigned int off, len;
+
+ /* check for end and drop resources from the last iteration */
+ if (!miter->__nents)
+ return false;
+
+ sg_miter_stop(miter);
+
+ /* get to the next sg if necessary. __offset is adjusted by stop */
+ if (miter->__offset == miter->__sg->length && --miter->__nents) {
+ miter->__sg = sg_next(miter->__sg);
+ miter->__offset = 0;
+ }
+
+ /* map the next page */
+ off = miter->__sg->offset + miter->__offset;
+ len = miter->__sg->length - miter->__offset;
+
+ miter->page = nth_page(sg_page(miter->__sg), off >> PAGE_SHIFT);
+ off &= ~PAGE_MASK;
+ miter->length = min_t(unsigned int, len, PAGE_SIZE - off);
+ miter->consumed = miter->length;
+
+ if (miter->__flags & SG_MITER_ATOMIC)
+ miter->addr = kmap_atomic(miter->page, KM_BIO_SRC_IRQ) + off;
+ else
+ miter->addr = kmap(miter->page) + off;
+
+ return true;
+}
+EXPORT_SYMBOL(sg_miter_next);
+
+/**
+ * sg_miter_stop - stop mapping iteration
+ * @miter: sg mapping iter to be stopped
+ *
+ * Description:
+ * Stops mapping iterator @miter. @miter should have been started
+ * started using sg_miter_start(). A stopped iteration can be
+ * resumed by calling sg_miter_next() on it. This is useful when
+ * resources (kmap) need to be released during iteration.
+ *
+ * Context:
+ * IRQ disabled if the SG_MITER_ATOMIC is set. Don't care otherwise.
+ */
+void sg_miter_stop(struct sg_mapping_iter *miter)
+{
+ WARN_ON(miter->consumed > miter->length);
+
+ /* drop resources from the last iteration */
+ if (miter->addr) {
+ miter->__offset += miter->consumed;
+
+ if (miter->__flags & SG_MITER_ATOMIC) {
+ WARN_ON(!irqs_disabled());
+ kunmap_atomic(miter->addr, KM_BIO_SRC_IRQ);
+ } else
+ kunmap(miter->addr);
+
+ miter->page = NULL;
+ miter->addr = NULL;
+ miter->length = 0;
+ miter->consumed = 0;
+ }
+}
+EXPORT_SYMBOL(sg_miter_stop);
+
+/**
* sg_copy_buffer - Copy data between a linear buffer and an SG list
* @sgl: The SG list
* @nents: Number of SG entries
@@ -309,56 +420,29 @@ EXPORT_SYMBOL(sg_alloc_table);
static size_t sg_copy_buffer(struct scatterlist *sgl, unsigned int nents,
void *buf, size_t buflen, int to_buffer)
{
- struct scatterlist *sg;
- size_t buf_off = 0;
- int i;
-
- WARN_ON(!irqs_disabled());
-
- for_each_sg(sgl, sg, nents, i) {
- struct page *page;
- int n = 0;
- unsigned int sg_off = sg->offset;
- unsigned int sg_copy = sg->length;
-
- if (sg_copy > buflen)
- sg_copy = buflen;
- buflen -= sg_copy;
-
- while (sg_copy > 0) {
- unsigned int page_copy;
- void *p;
-
- page_copy = PAGE_SIZE - sg_off;
- if (page_copy > sg_copy)
- page_copy = sg_copy;
-
- page = nth_page(sg_page(sg), n);
- p = kmap_atomic(page, KM_BIO_SRC_IRQ);
-
- if (to_buffer)
- memcpy(buf + buf_off, p + sg_off, page_copy);
- else {
- memcpy(p + sg_off, buf + buf_off, page_copy);
- flush_kernel_dcache_page(page);
- }
-
- kunmap_atomic(p, KM_BIO_SRC_IRQ);
-
- buf_off += page_copy;
- sg_off += page_copy;
- if (sg_off == PAGE_SIZE) {
- sg_off = 0;
- n++;
- }
- sg_copy -= page_copy;
+ unsigned int offset = 0;
+ struct sg_mapping_iter miter;
+
+ sg_miter_start(&miter, sgl, nents, SG_MITER_ATOMIC);
+
+ while (sg_miter_next(&miter) && offset < buflen) {
+ unsigned int len;
+
+ len = min(miter.length, buflen - offset);
+
+ if (to_buffer)
+ memcpy(buf + offset, miter.addr, len);
+ else {
+ memcpy(miter.addr, buf + offset, len);
+ flush_kernel_dcache_page(miter.page);
}
- if (!buflen)
- break;
+ offset += len;
}
- return buf_off;
+ sg_miter_stop(&miter);
+
+ return offset;
}
/**
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