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Re: [qemu-s390x] [PATCH 04/15] s390-bios: Extend find_dev() for non-virt

From: Jason J. Herne
Subject: Re: [qemu-s390x] [PATCH 04/15] s390-bios: Extend find_dev() for non-virtio devices
Date: Wed, 13 Feb 2019 08:59:08 -0500
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.2.1

On 2/11/19 11:38 AM, Thomas Huth wrote:
On 2019-01-29 14:29, Jason J. Herne wrote:
We need a method for finding the subchannel of a dasd device. Let's
modify find_dev to handle this since it mostly does what we need. Up to
this point find_dev has been specific to only virtio devices.

Signed-off-by: Jason J. Herne <address@hidden>
Acked-by: Halil Pasic <address@hidden>
  pc-bios/s390-ccw/main.c | 16 +++++++++++-----
  1 file changed, 11 insertions(+), 5 deletions(-)

diff --git a/pc-bios/s390-ccw/main.c b/pc-bios/s390-ccw/main.c
index 67df421..7e3f65e 100644
--- a/pc-bios/s390-ccw/main.c
+++ b/pc-bios/s390-ccw/main.c
@@ -49,6 +49,12 @@ unsigned int get_loadparm_index(void)
      return atoui(loadparm_str);
+ * 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.
+ */
  static bool find_dev(Schib *schib, int dev_no)
      int i, r;
@@ -62,15 +68,15 @@ static bool find_dev(Schib *schib, int dev_no)
          if (!schib->pmcw.dnv) {
-        if (!virtio_is_supported(blk_schid)) {
-            continue;
-        }
          /* Skip net devices since no IPLB is created and therefore no
-         * no network bootloader has been loaded
+         * network bootloader has been loaded
-        if (virtio_get_device_type() == VIRTIO_ID_NET && dev_no < 0) {
+        if (virtio_is_supported(blk_schid) &&
+            virtio_get_device_type() == VIRTIO_ID_NET && dev_no < 0) {
          if ((dev_no < 0) || (schib->pmcw.dev == dev_no)) {
              return true;

Not sure whether this really works as expected? If dev_no is -1, this
used to return the first supported virtio device. Now it returns the
first device that could be found - but how are we sure that we can boot
from that device?

How could we ever be sure we could boot from the first virtio device? The dev_no=1 case means we don't know which device to boot from so we're guessing. The only thing that is changing here is that we're allowing non-virtio devices as well. We do this because we now support booting from a device type that is not virtio.

-- Jason J. Herne (address@hidden)

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