tftp: clarify what is actually OACK m_len

The current computation is a bit convoluted, and doesn't reflect >0.
What is actually computed is sizeof():

struct tftp_t {
    struct udphdr udp;
    uint16_t tp_op;
    union {
        ...
        char tp_buf[TFTP_BLOCKSIZE_MAX + 2];
    } x;
}
- sizeof(struct udphdr) == udp field
- (TFTP_BLOCKSIZE_MAX + 2) == tp_buf field
+ n

What remains is: G_SIZEOF_MEMBER(struct tftp_t, tp_op) + n.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Samuel Thibault <samuel.thibault@ens-lyon.org>

1 files changed, 1 insertions, 2 deletions

diff --git a/src/tftp.c b/src/tftp.c
index e52e71b..4d9ee1f 100644
--- a/src/tftp.c
+++ b/src/tftp.c
@@ -193,8 +193,7 @@ static int tftp_send_oack(struct tftp_session *spt, const char *keys[],
              1;
     }
 
-    m->m_len = sizeof(struct tftp_t) - (TFTP_BLOCKSIZE_MAX + 2) + n -
-               sizeof(struct udphdr);
+    m->m_len = G_SIZEOF_MEMBER(struct tftp_t, tp_op) + n;
     tftp_udp_output(spt, m, recv_tp);
 
     return 0;