[PATCH for-5.2 5/6] pc-bios/s390-ccw: Scan through all boot devices if none has been specified

[Thomas Huth <thuth@redhat.com>]

If no boot device has been specified (via "bootindex=..."), the s390-ccw
bios scans through all devices to find a bootable device. But so far, it
stops at the very first block device (including virtio-scsi controllers
without attached devices) that it finds, no matter whether it is bootable
or not. That leads to some weird situatation where it is e.g. possible
to boot via:

 qemu-system-s390x -hda /path/to/disk.qcow2

but not if there is e.g. a virtio-scsi controller specified before:

 qemu-system-s390x -device virtio-scsi -hda /path/to/disk.qcow2

While using "bootindex=..." is clearly the preferred way of booting
on s390x, we still can make the life for the users at least a little
bit easier if we look at all available devices to find a bootable one.

Buglink: https://bugzilla.redhat.com/show_bug.cgi?id=1846975
Signed-off-by: Thomas Huth <thuth@redhat.com>
---
 pc-bios/s390-ccw/main.c | 46 +++++++++++++++++++++++++++--------------
 1 file changed, 31 insertions(+), 15 deletions(-)

diff --git a/pc-bios/s390-ccw/main.c b/pc-bios/s390-ccw/main.c
index 3cd01cd80f..0af872f9e3 100644
--- a/pc-bios/s390-ccw/main.c
+++ b/pc-bios/s390-ccw/main.c
@@ -182,20 +182,8 @@ static void boot_setup(void)
 static void find_boot_device(void)
 {
     VDev *vdev = virtio_get_device();
-    int ssid;
     bool found;
 
-    if (!have_iplb) {
-        for (ssid = 0; ssid < 0x3; ssid++) {
-            blk_schid.ssid = ssid;
-            found = find_subch(-1);
-            if (found) {
-                return;
-            }
-        }
-        panic("Could not find a suitable boot device (none specified)\n");
-    }
-
     switch (iplb.pbt) {
     case S390_IPL_TYPE_CCW:
         debug_print_int("device no. ", iplb.ccw.devno);
@@ -260,14 +248,42 @@ static void ipl_boot_device(void)
     }
 }
 
+/*
+ * No boot device has been specified, so we have to scan through the
+ * channels to find one.
+ */
+static void probe_boot_device(void)
+{
+    int ssid, sch_no, ret;
+
+    for (ssid = 0; ssid < 0x3; ssid++) {
+        blk_schid.ssid = ssid;
+        for (sch_no = 0; sch_no < 0x10000; sch_no++) {
+            ret = check_sch_no(-1, sch_no);
+            if (ret < 0) {
+                break;
+            }
+            if (ret == true) {
+                ipl_boot_device();      /* Only returns if unsuccessful */
+            }
+        }
+    }
+
+    sclp_print("Could not find a suitable boot device (none specified)\n");
+}
+
 int main(void)
 {
     sclp_setup();
     css_setup();
     boot_setup();
-    find_boot_device();
-    enable_subchannel(blk_schid);
-    ipl_boot_device();
+    if (have_iplb) {
+        find_boot_device();
+        enable_subchannel(blk_schid);
+        ipl_boot_device();
+    } else {
+        probe_boot_device();
+    }
 
     panic("Failed to load OS from hard disk\n");
     return 0; /* make compiler happy */
-- 
2.18.1