ahci: Reorder error cases in handle_cmd

Error checking in ahci's handle_cmd is re-ordered so that we
initialize as few things as possible before we've done our
sanity checking. This simplifies returning from this call
in case of an error.

A check to make sure the DMA memory map succeeds with the
correct size is also added, and the debug print of the
command fis is cleaned up with its size corrected.
Signed-off-by: NJohn Snow <jsnow@redhat.com>
Reviewed-by: NPaolo Bonzini <pbonzini@redhat.com>
Message-id: 1415058979-16604-4-git-send-email-jsnow@redhat.com
Signed-off-by: NStefan Hajnoczi <stefanha@redhat.com>

hw/ide/ahci.c

@@ -961,38 +961,37 @@ static int handle_cmd(AHCIState *s, int port, int slot)
         return -1;
     }
 
-    cmd = &((AHCICmdHdr *)s->dev[port].lst)[slot];
-
     if (!s->dev[port].lst) {
         DPRINTF(port, "error: lst not given but cmd handled");
         return -1;
     }
-
+    cmd = &((AHCICmdHdr *)s->dev[port].lst)[slot];
     /* remember current slot handle for later */
     s->dev[port].cur_cmd = cmd;
 
+    /* The device we are working for */
+    ide_state = &s->dev[port].port.ifs[0];
+    if (!ide_state->blk) {
+        DPRINTF(port, "error: guest accessed unused port");
+        return -1;
+    }
+
     opts = le32_to_cpu(cmd->opts);
     tbl_addr = le64_to_cpu(cmd->tbl_addr);
-
     cmd_len = 0x80;
     cmd_fis = dma_memory_map(s->as, tbl_addr, &cmd_len,
                              DMA_DIRECTION_FROM_DEVICE);
-
     if (!cmd_fis) {
         DPRINTF(port, "error: guest passed us an invalid cmd fis\n");
         return -1;
-    }
-
-    /* The device we are working for */
-    ide_state = &s->dev[port].port.ifs[0];
-
-    if (!ide_state->blk) {
-        DPRINTF(port, "error: guest accessed unused port");
+    } else if (cmd_len != 0x80) {
+        ahci_trigger_irq(s, &s->dev[port], PORT_IRQ_HBUS_ERR);
+        DPRINTF(port, "error: dma_memory_map failed: "
+                "(len(%02"PRIx64") != 0x80)\n",
+                cmd_len);
         goto out;
     }
-
-    debug_print_fis(cmd_fis, 0x90);
-    //debug_print_fis(cmd_fis, (opts & AHCI_CMD_HDR_CMD_FIS_LEN) * 4);
+    debug_print_fis(cmd_fis, 0x80);
 
     switch (cmd_fis[0]) {
         case SATA_FIS_TYPE_REGISTER_H2D: