[PATCH v3 1/6] SUNRPC: Introduce xdr_stream_move_subsegment()

Anna Schumaker
2022-07-15T18:44:39Z

From: Anna Schumaker <Anna.Schumaker@Netapp.com>

I do this by creating an xdr subsegment for the range we will be
operating over. This lets me shift data to the correct place without
potentially overwriting anything already there.

Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
---
include/linux/sunrpc/xdr.h | 2 ++
net/sunrpc/xdr.c | 59 ++++++++++++++++++++++++++++++++++++++
2 files changed, 61 insertions(+)

diff --git a/include/linux/sunrpc/xdr.h b/include/linux/sunrpc/xdr.h
index 5860f32e3958..7dcc6c31fe29 100644
--- a/include/linux/sunrpc/xdr.h
+++ b/include/linux/sunrpc/xdr.h
@@ -262,6 +262,8 @@ extern unsigned int xdr_align_data(struct xdr_stream *, unsigned int offset, uns
extern unsigned int xdr_expand_hole(struct xdr_stream *, unsigned int offset, unsigned int length);
extern bool xdr_stream_subsegment(struct xdr_stream *xdr, struct xdr_buf *subbuf,
unsigned int len);
+extern unsigned int xdr_stream_move_subsegment(struct xdr_stream *xdr, unsigned int offset,
+ unsigned int target, unsigned int length);

/**
* xdr_set_scratch_buffer - Attach a scratch buffer for decoding data.
diff --git a/net/sunrpc/xdr.c b/net/sunrpc/xdr.c
index 5d2b3e6979fb..8ba11a754297 100644
--- a/net/sunrpc/xdr.c
+++ b/net/sunrpc/xdr.c
@@ -775,6 +775,34 @@ static void xdr_buf_pages_shift_left(const struct xdr_buf *buf,
xdr_buf_tail_copy_left(buf, 0, len - buf->page_len, shift);
}

+static void xdr_buf_head_shift_left(const struct xdr_buf *buf,
+ unsigned int base, unsigned int len,
+ unsigned int shift)
+{
+ const struct kvec *head = buf->head;
+ unsigned int bytes;
+
+ if (!shift || !len)
+ return;
+
+ if (shift > base) {
+ bytes = (shift - base);
+ if (bytes >= len)
+ return;
+ base += bytes;
+ len -= bytes;
+ }
+
+ if (base < head->iov_len) {
+ bytes = min_t(unsigned int, len, head->iov_len - base);
+ memmove(head->iov_base + (base - shift),
+ head->iov_base + base, bytes);
+ base += bytes;
+ len -= bytes;
+ }
+ xdr_buf_pages_shift_left(buf, base - head->iov_len, len, shift);
+}
+
/**
* xdr_shrink_bufhead
* @buf: xdr_buf
@@ -1680,6 +1708,37 @@ bool xdr_stream_subsegment(struct xdr_stream *xdr, struct xdr_buf *subbuf,
}
EXPORT_SYMBOL_GPL(xdr_stream_subsegment);

+/**
+ * xdr_stream_move_subsegment - Move part of a stream to another position
+ * @xdr: the source xdr_stream
+ * @offset: the source offset of the segment
+ * @target: the target offset of the segment
+ * @length: the number of bytes to move
+ *
+ * Moves @length bytes from @offset to @target in the xdr_stream, overwriting
+ * anything in its space. Returns the number of bytes in the segment.
+ */
+unsigned int xdr_stream_move_subsegment(struct xdr_stream *xdr, unsigned int offset,
+ unsigned int target, unsigned int length)
+{
+ struct xdr_buf buf;
+ unsigned int shift;
+
+ if (offset < target) {
+ shift = target - offset;
+ if (xdr_buf_subsegment(xdr->buf, &buf, offset, shift + length) < 0)
+ return 0;
+ xdr_buf_head_shift_right(&buf, 0, length, shift);
+ } else if (offset > target) {
+ shift = offset - target;
+ if (xdr_buf_subsegment(xdr->buf, &buf, target, shift + length) < 0)
+ return 0;
+ xdr_buf_head_shift_left(&buf, shift, length, shift);
+ }
+ return length;
+}
+EXPORT_SYMBOL_GPL(xdr_stream_move_subsegment);
+
/**
* xdr_buf_trim - lop at most "len" bytes off the end of "buf"
* @buf: buf to be trimmed
--
2.37.1