This lets callers specify a region of memory to read from or write to with
an array of page/offset/len tuples. There have been specific requests to
do this from servers which want to do O_DIRECT from the kernel. (knfsd?)
This could also be used by places which currently hold a kmap() and call
fop->write. ecryptfs_write_lower_page_segment() is one such caller.
---
fs/rwmem.c | 66 +++++++++++++++++++++++++++++++++++++++++++++++++
include/linux/rwmem.h | 16 ++++++++++++
2 files changed, 82 insertions(+), 0 deletions(-)
diff --git a/fs/rwmem.c b/fs/rwmem.c
index 0433ba4..c87e8a4 100644
--- a/fs/rwmem.c
+++ b/fs/rwmem.c
@@ -90,3 +90,69 @@ struct rwmem_ops rwmem_iovec_ops = {
.seg_bytes = rwmem_iovec_seg_bytes,
.get_seg_pages = rwmem_iovec_get_seg_pages,
};
+
+void rwmem_pages_init(struct rwmem *rwm)
+{
+ struct rwmem_pages *rwp = container_of(rwm, struct rwmem_pages, rwmem);
+ struct pgol *pgol;
+ unsigned long i;
+
+ rwm->total_bytes = 0;
+ rwm->nr_pages = rwm->nr_segs;
+ rwm->boundary_bits = 0;
+
+ for (i = 0; i < rwm->nr_segs; i++) {
+ pgol = &rwp->pgol[i];
+
+ rwm->total_bytes += pgol->len;
+ rwm->boundary_bits |= pgol->offset | pgol->len;
+ }
+}
+
+/*
+ * Returns the offset of the start of a segment within its first page.
+ */
+unsigned long rwmem_pages_seg_page_offset(struct rwmem *rwm, unsigned long i)
+{
+ struct rwmem_pages *rwp = container_of(rwm, struct rwmem_pages, rwmem);
+ BUG_ON(i >= rwm->nr_segs);
+ return rwp->pgol[i].offset;
+}
+
+/*
+ * Returns the total bytes in the given segment.
+ */
+unsigned long rwmem_pages_seg_bytes(struct rwmem *rwm, unsigned long i)
+{
+ struct rwmem_pages *rwp = container_of(rwm, struct rwmem_pages, rwmem);
+ BUG_ON(i >= rwm->nr_segs);
+ return rwp->pgol[i].len;
+}
+
+/*
+ * For now each page is its own seg.
+ */
+int rwmem_pages_get_seg_pages(struct rwmem *rwm, unsigned long i,
+ unsigned long *cursor, struct page **pages,
+ unsigned long max_pages, int write)
+{
+ struct rwmem_pages *rwp = container_of(rwm, struct rwmem_pages, rwmem);
+ int ret = 0;
+
+ BUG_ON(i >= rwm->nr_segs);
+ BUG_ON(*cursor != 0);
+
+ if (max_pages) {
+ pages[0] = rwp->pgol[i].page;
+ get_page(pages[0]);
+ ret = 1;
+ }
+ return ret;
+}
+
+struct rwmem_ops rwmem_pages_ops = {
+ .init = rwmem_pages_init,
+ .seg_page_offset = rwmem_pages_seg_page_offset,
+ .seg_bytes = rwmem_pages_seg_bytes,
+ .get_seg_pages = rwmem_pages_get_seg_pages,
+};
diff --git a/include/linux/rwmem.h b/include/linux/rwmem.h
index 666f9f4..47019f0 100644
--- a/include/linux/rwmem.h
+++ b/include/linux/rwmem.h
@@ -26,4 +26,20 @@ struct rwmem_iovec {
};
struct rwmem_ops rwmem_iovec_ops;
+/*
+ * How many times do we need this in subsystems before we make a universal
+ * struct? (bio_vec, skb_frag_struct, pipe_buffer)
+ */
+struct pgol {
+ struct page *page;
+ unsigned int offset;
+ unsigned int len;
+};
+
+struct rwmem_pages {
+ struct rwmem rwmem;
+ struct pgol *pgol;
+};
+struct rwmem_ops rwmem_pages_ops;
+
#endif
--
1.5.2.2
-
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