libqos/ahci: set the NCQ tag on command_commit

NCQ commands have the concept of a "TAG" that they need to set,
but in the AHCI world, it is mandated that the TAG always match
the command slot that you executed the NCQ from.

See AHCI 9.3.1.1.5.2 "Native Queued Commands".
Signed-off-by: NJohn Snow <jsnow@redhat.com>
Reviewed-by: NStefan Hajnoczi <stefanha@redhat.com>
Message-id: 1435016308-6150-14-git-send-email-jsnow@redhat.com

tests/libqos/ahci.c

@@ -857,6 +857,11 @@ void ahci_command_commit(AHCIQState *ahci, AHCICommand *cmd, uint8_t port)
     cmd->port = port;
     cmd->slot = ahci_pick_cmd(ahci, port);
 
+    if (cmd->props->ncq) {
+        NCQFIS *nfis = (NCQFIS *)&cmd->fis;
+        nfis->tag = (cmd->slot << 3) & 0xFC;
+    }
+
     /* Create a buffer for the command table */
     prdtl = size_to_prdtl(cmd->xbytes, cmd->prd_size);
     table_size = CMD_TBL_SIZ(prdtl);