pc-bios/s390-ccw: Move the inner logic of find_subch() to a separate function

Move the code to a separate function to be able to re-use it from a
different spot later.

Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Message-Id: <20200806105349.632-5-thuth@redhat.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Reviewed-by: Janosch Frank <frankja@linux.ibm.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>

pc-bios/s390-ccw/main.c

@@ -51,29 +51,19 @@ unsigned int get_loadparm_index(void)
     return atoui(loadparm_str);
 }
 
-/*
+static int is_dev_possibly_bootable(int dev_no, int sch_no)
- * Find the subchannel connected to the given device (dev_no) and fill in the
- * subchannel information block (schib) with the connected subchannel's info.
- * NOTE: The global variable blk_schid is updated to contain the subchannel
- * information.
- *
- * If the caller gives dev_no=-1 then the user did not specify a boot device.
- * In this case we'll just use the first potentially bootable device we find.
- */
-static bool find_subch(int dev_no)
 {
-    Schib schib;
-    int i, r;
     bool is_virtio;
+    Schib schib;
+    int r;
 
-    for (i = 0; i < 0x10000; i++) {
+    blk_schid.sch_no = sch_no;
-        blk_schid.sch_no = i;
     r = stsch_err(blk_schid, &schib);
-        if ((r == 3) || (r == -EIO)) {
+    if (r == 3 || r == -EIO) {
-            break;
+        return -ENODEV;
     }
     if (!schib.pmcw.dnv) {
-            continue;
+        return false;
     }
 
     enable_subchannel(blk_schid);
@@ -85,7 +75,7 @@ static bool find_subch(int dev_no)
      */
     is_virtio = virtio_is_supported(blk_schid);
 
-        /* No specific devno given, just return 1st possibly bootable device */
+    /* No specific devno given, just return whether the device is possibly bootable */
     if (dev_no < 0) {
         switch (cutype) {
         case CU_TYPE_VIRTIO:
@@ -98,12 +88,12 @@ static bool find_subch(int dev_no)
                     return true;
                 }
             }
-                continue;
+            return false;
         case CU_TYPE_DASD_3990:
         case CU_TYPE_DASD_2107:
             return true;
         default:
-                continue;
+            return false;
         }
     }
 
@@ -111,6 +101,31 @@ static bool find_subch(int dev_no)
     if (schib.pmcw.dev == dev_no) {
         return true;
     }
+
+    return false;
+}
+
+/*
+ * Find the subchannel connected to the given device (dev_no) and fill in the
+ * subchannel information block (schib) with the connected subchannel's info.
+ * NOTE: The global variable blk_schid is updated to contain the subchannel
+ * information.
+ *
+ * If the caller gives dev_no=-1 then the user did not specify a boot device.
+ * In this case we'll just use the first potentially bootable device we find.
+ */
+static bool find_subch(int dev_no)
+{
+    int i, r;
+
+    for (i = 0; i < 0x10000; i++) {
+        r = is_dev_possibly_bootable(dev_no, i);
+        if (r < 0) {
+            break;
+        }
+        if (r == true) {
+            return true;
+        }
     }
 
     return false;