[Qemu-devel] [PATCH v2] util: Fix assertion in iov_copy() upon zero 'bytes' and non-zero 'offset'

[Shmulik Ladkani <shmulik.ladkani@oracle.com>]

From: Shmulik Ladkani <shmulik.ladkani@ravellosystems.com>

In cases where iov_copy() is passed with zero 'bytes' argument and a
non-zero 'offset' argument, nothing gets copied - as expected.

However no copy iterations are performed, so 'offset' is left
unaltered, leading to the final assert(offset == 0) to fail.

Instead, change the loop condition to continue as long as 'offset || bytes',
similar to other iov_* functions.

This ensures 'offset' gets zeroed (even if no actual copy is made),
unless it is beyond end of source iov - which is asserted.

Signed-off-by: Shmulik Ladkani <shmulik.ladkani@ravellosystems.com>
---
 util/iov.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

 v2: Instead of relaxing the assertion, modify loop condition,
     as suggested by Paolo

diff --git a/util/iov.c b/util/iov.c
index 003fcce..74e6ca8 100644
--- a/util/iov.c
+++ b/util/iov.c
@@ -247,7 +247,8 @@ unsigned iov_copy(struct iovec *dst_iov, unsigned int dst_iov_cnt,
 {
     size_t len;
     unsigned int i, j;
-    for (i = 0, j = 0; i < iov_cnt && j < dst_iov_cnt && bytes; i++) {
+    for (i = 0, j = 0;
+         i < iov_cnt && j < dst_iov_cnt && (offset || bytes); i++) {
         if (offset >= iov[i].iov_len) {
             offset -= iov[i].iov_len;
             continue;
-- 
1.9.1