[PATCH 04/11] sio: fix passing negative size_t to sio_add_to_iov

[Vladislav Shpilevoy <v.shpilevoy@tarantool.org>]

sio_add_to_iov moves struct iov position on a
specified offset, positive or negative. But its offset
argument has size_t type, which is unsigned. Make it
be ssize_t.

This worked before thanks to how negative numbers are
stored. For example, consider

uint8_t value = 100;
uint8_t offset = -5;

Value is stored as  0110 0100.
Offset is stored as 1111 1011. (Yes, 1011, not 1010).

Sum of the values above is 0001 0101 1111 - first quad
overflows and is truncated, so the result is
0101 1111 = 95 - correct.
---
 src/sio.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/sio.h b/src/sio.h
index ab0a243cd..ff383aa36 100644
--- a/src/sio.h
+++ b/src/sio.h
@@ -84,7 +84,7 @@ sio_move_iov(struct iovec *iov, size_t nwr, size_t *iov_len)
  * to adjust to a partial write.
  */
 static inline void
-sio_add_to_iov(struct iovec *iov, size_t size)
+sio_add_to_iov(struct iovec *iov, ssize_t size)
 {
 	iov->iov_len += size;
 	iov->iov_base = (char *) iov->iov_base - size;
-- 
2.17.2 (Apple Git-113)