Encoding a hole followed by data takes up more space than the xdr head
has allocated to it. As a result, the data segment will already be some
number of bytes on the page (usually 20 in this case), so a shift left
operation is needed to decode data to the right location.
xdr_shift_hole() will be called to insert a hole into the page data
by shifting contents over by some number of bytes and then zeroing the
requested range.
Ideally, I want to use the offset provided by READ_PLUS to place data
exactly where it needs to be. I have a rough (non-functioning) patch
for this that I want to hack on a little bit more before submitting.
---
include/linux/sunrpc/xdr.h | 1 +
net/sunrpc/xdr.c | 115 ++++++++++++++++++++++++++++++++++++++++++++-
2 files changed, 115 insertions(+), 1 deletion(-)
diff --git a/include/linux/sunrpc/xdr.h b/include/linux/sunrpc/xdr.h
index 15f9204..1deb79b 100644
--- a/include/linux/sunrpc/xdr.h
+++ b/include/linux/sunrpc/xdr.h
@@ -227,6 +227,7 @@ extern unsigned int xdr_read_pages(struct xdr_stream *xdr, unsigned int len);
extern void xdr_enter_page(struct xdr_stream *xdr, unsigned int len);
extern int xdr_process_buf(struct xdr_buf *buf, unsigned int offset, unsigned int len, int (*actor)(struct scatterlist *, void *), void *data);
+extern void xdr_shift_hole(struct xdr_stream *, size_t, size_t);
#endif /* __KERNEL__ */
#endif /* _SUNRPC_XDR_H_ */
diff --git a/net/sunrpc/xdr.c b/net/sunrpc/xdr.c
index 1504bb1..96973e3 100644
--- a/net/sunrpc/xdr.c
+++ b/net/sunrpc/xdr.c
@@ -219,6 +219,95 @@ _shift_data_right_pages(struct page **pages, size_t pgto_base,
} while ((len -= copy) != 0);
}
+/*
+ * _shift_data_left_pages
+ * @pages: vector of pages containing both the source and dest memory area
+ * @pgto_base: page vector address of destination
+ * @pgfrom_base: page vector address of source
+ * @len: number of bytes to move
+ *
+ * Note: This function does not copy data out of the tail. It only shifts
+ * already in the pages.
+ */
+static void
+_shift_data_left_pages(struct page **pages, size_t pgto_base,
+ size_t pgfrom_base, size_t len)
+{
+ struct page **pgfrom, **pgto;
+ char *vto, *vfrom;
+ size_t copy;
+
+ BUG_ON(pgto_base >= pgfrom_base);
+
+ pgto = pages + (pgto_base >> PAGE_CACHE_SHIFT);
+ pgfrom = pages + (pgfrom_base >> PAGE_CACHE_SHIFT);
+
+ do {
+ /* Are any pointers crossing a page boundary? */
+ if (pgto_base == PAGE_SIZE) {
+ pgto_base = 0;
+ pgto++;
+ }
+ if (pgfrom_base == PAGE_SIZE) {
+ pgfrom_base = 0;
+ pgfrom++;
+ }
+
+ copy = len;
+ if (copy > PAGE_SIZE - pgto_base)
+ copy = PAGE_SIZE - pgto_base;
+ if (copy > PAGE_SIZE - pgfrom_base)
+ copy = PAGE_SIZE - pgfrom_base;
+
+ vto = kmap_atomic(*pgto);
+ if (*pgto != *pgfrom) {
+ vfrom = kmap_atomic(*pgfrom);
+ memcpy(vto + pgto_base, vfrom + pgfrom_base, copy);
+ kunmap_atomic(vfrom);
+ };
+ if (*pgto == *pgfrom)
+ memmove(vto + pgto_base, vto + pgfrom_base, copy);
+ flush_dcache_page(*pgto);
+ kunmap_atomic(vto);
+
+ pgto_base += copy;
+ pgfrom_base += copy;
+
+ } while ((len -= copy) != 0);
+}
+
+/**
+ * _zero_data_pages
+ * @pages: array of pages
+ * @pgbase: beginning page vector address
+ * @len: length
+ */
+static void
+_zero_data_pages(struct page **pages, size_t pgbase, size_t len)
+{
+ struct page **page;
+ char *vpage;
+ size_t zero;
+
+ page = pages + (pgbase >> PAGE_CACHE_SHIFT);
+ pgbase &= ~PAGE_CACHE_MASK;
+
+ do {
+ zero = len;
+ if (pgbase + zero > PAGE_SIZE)
+ zero = PAGE_SIZE - pgbase;
+
+ vpage = kmap_atomic(*page);
+ memset(vpage + pgbase, 0, zero);
+ flush_dcache_page(*page);
+ kunmap_atomic(vpage);
+
+ page++;
+ pgbase = 0;
+
+ } while ((len -= zero) != 0);
+}
+
/**
* _copy_to_pages
* @pages: array of pages
@@ -434,6 +523,22 @@ xdr_shift_buf(struct xdr_buf *buf, size_t len)
}
EXPORT_SYMBOL_GPL(xdr_shift_buf);
+static unsigned int xdr_align_pages(struct xdr_stream *, unsigned int);
+void
+xdr_shift_hole(struct xdr_stream *xdr, size_t offset, size_t length)
+{
+ struct xdr_buf *buf = xdr->buf;
+
+ if (buf->page_len == length)
+ xdr_align_pages(xdr, length);
+ else
+ _shift_data_right_pages(buf->pages, buf->page_base + length,
+ buf->page_base, buf->page_len - length);
+
+ _zero_data_pages(buf->pages, buf->page_base, length);
+}
+EXPORT_SYMBOL_GPL(xdr_shift_hole);
+
/**
* xdr_stream_pos - Return the current offset from the start of the xdr_stream
* @xdr: pointer to struct xdr_stream
@@ -727,6 +832,12 @@ __be32 * xdr_inline_decode(struct xdr_stream *xdr, size_t nbytes)
}
EXPORT_SYMBOL_GPL(xdr_inline_decode);
+static void xdr_align_pages_left(struct xdr_buf *buf, unsigned int len)
+{
+ _shift_data_left_pages(buf->pages, buf->page_base,
+ buf->page_base + len, buf->page_len - len);
+}
+
static unsigned int xdr_align_pages(struct xdr_stream *xdr, unsigned int len)
{
struct xdr_buf *buf = xdr->buf;
@@ -741,7 +852,9 @@ static unsigned int xdr_align_pages(struct xdr_stream *xdr, unsigned int len)
if (iov->iov_len > cur) {
xdr_shrink_bufhead(buf, iov->iov_len - cur);
xdr->nwords = XDR_QUADLEN(buf->len - cur);
- }
+ /* cur points somewhere on the page array */
+ } else if (cur != iov->iov_len)
+ xdr_align_pages_left(buf, cur - iov->iov_len);
if (nwords > xdr->nwords) {
nwords = xdr->nwords;
--
1.8.5.2
--
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