[Qemu-devel] [PATCH] util: Relax assertion in iov_copy()

[Shmulik Ladkani]

From: Shmulik Ladkani <address@hidden>

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

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

Relax the assertion: if j (number of dst elements assigned) is zero, no
need to err.

Only if j!=0 (some dst elements assigned) AND offset!=0 we should err.

Signed-off-by: Shmulik Ladkani <address@hidden>
---
 util/iov.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Flow that led to the assertion was:
  net_tx_pkt_rebuild_payload()
    iov_copy(... , pkt->payload_len)

where pkt->payload_len was correctly calculated to be 0 (a packet
carrying just ipv4 header, without any payload).

An alternative is to place the below code, early in iov_copy():
    if (!bytes)
        return 0;

diff --git a/util/iov.c b/util/iov.c
index 003fcce..17de52d 100644
--- a/util/iov.c
+++ b/util/iov.c
@@ -260,7 +260,7 @@ unsigned iov_copy(struct iovec *dst_iov, unsigned int 
dst_iov_cnt,
         bytes -= len;
         offset = 0;
     }
-    assert(offset == 0);
+    assert(j == 0 || offset == 0);
     return j;
 }
 
-- 
1.9.1