[Qemu-devel] [PATCH] slirp: add checksum support to NC-SI backend

[Cédric Le Goater]

The checksum field of a NC-SI packet contains a value that may be
included in each command and response. The verification is optional
but the Linux driver does so when a non-zero value is provided. Let's
extend the model to compute the checksum value and exercise a little
more the Linux driver.

See section "8.2.2.3 - 2's Complement Checksum Compensation" in the
Network Controller Sideband Interface (NC-SI) Specification for more
details.

Signed-off-by: Cédric Le Goater <address@hidden>
---
 slirp/ncsi.c | 29 +++++++++++++++++++++++++----
 1 file changed, 25 insertions(+), 4 deletions(-)

diff --git a/slirp/ncsi.c b/slirp/ncsi.c
index d12ba3e494b0..81c6bc5576d3 100644
--- a/slirp/ncsi.c
+++ b/slirp/ncsi.c
@@ -8,9 +8,23 @@
  */
 #include "qemu/osdep.h"
 #include "slirp.h"
+#include "net/checksum.h"
 
 #include "ncsi-pkt.h"
 
+static uint32_t ncsi_calculate_checksum(unsigned char *data, int len)
+{
+    uint32_t checksum = 0;
+    int i;
+
+    for (i = 0; i < len; i += 2) {
+        checksum += (((uint32_t)data[i] << 8) | data[i + 1]);
+    }
+
+    checksum = (~checksum + 1);
+    return checksum;
+}
+
 /* Get Capabilities */
 static int ncsi_rsp_handler_gc(struct ncsi_rsp_pkt_hdr *rnh)
 {
@@ -87,6 +101,9 @@ void ncsi_input(Slirp *slirp, const uint8_t *pkt, int 
pkt_len)
         (ncsi_reply + ETH_HLEN);
     const struct ncsi_rsp_handler *handler = NULL;
     int i;
+    int ncsi_rsp_len = sizeof(*nh);
+    uint32_t checksum;
+    uint32_t *pchecksum;
 
     memset(ncsi_reply, 0, sizeof(ncsi_reply));
 
@@ -116,15 +133,19 @@ void ncsi_input(Slirp *slirp, const uint8_t *pkt, int 
pkt_len)
             /* TODO: handle errors */
             handler->handler(rnh);
         }
+        ncsi_rsp_len += handler->payload;
     } else {
         rnh->common.length = 0;
         rnh->code          = htons(NCSI_PKT_RSP_C_UNAVAILABLE);
         rnh->reason        = htons(NCSI_PKT_RSP_R_UNKNOWN);
     }
 
-    /* TODO: add a checksum at the end of the frame but the specs
-     * allows it to be zero */
+    /* add a checksum at the end of the frame (the specs allows it to
+     * be zero */
+    checksum = ncsi_calculate_checksum((unsigned char *) rnh, ncsi_rsp_len);
+    pchecksum = (uint32_t *)((void *) rnh + ncsi_rsp_len);
+    *pchecksum = htonl(checksum);
+    ncsi_rsp_len += 4;
 
-    slirp_output(slirp->opaque, ncsi_reply, ETH_HLEN + sizeof(*nh) +
-                 (handler ? handler->payload : 0) + 4);
+    slirp_output(slirp->opaque, ncsi_reply, ETH_HLEN + ncsi_rsp_len);
 }
-- 
2.7.4