[Xen-devel] [PATCH 1 of 1] mini-os: PV fronted MUST be in XenbusStateConnected not XenbusStateInitialized during init

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

# HG changeset patch
# User Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
# Date 1277908182 14400
# Node ID 76e7d0258f65e4ab1b105cd70a96f2a411d5ca22
# Parent  a24dbfcbdf695f49867d5881ea20ab40f18aea98
mini-os: PV fronted MUST be in XenbusStateConnected not XenbusStateInitialized 
during init.

With the QEMU change 805ed3b20492d2f4bb465bfda65cedd286e23209
("Wait for frontend state Connected before connecting the backend"),
where QEMU backend (say VNC framebuffer) will ONLY call ops->connect
(which when successfull, will move the backend state from XenbusStateInitWait
to XenbusStateConnected) when the frontend state is in XenbusStateConnected.

Previous to that git commit it would call ops->connect also
if the frontend was in XenbusStateInitialized state.

Without this patch, the MiniOS (in my case pvgrub) would hang
in the fbfront and kbfront threads waiting for the backend to change
its state from InitWait to Connected. Which the backend would not do
as the ops->connect in QEMU was never called.

The c/s 21260 "mini-os: Revert 21106:b20f897d6010 "Fix xenbus initialisation"
fixes this for the blkfront and netfront. Unfortunately
it did not fix it for the fbfront, kbdfront and pcifront which
this patch does.

The patch fixes pv-grub hanging at:
"
******************* FBFRONT for device/vfb/0 **********


******************* KBDFRONT for device/vkbd/0 **********
" and makes it now go to:
"
******************* FBFRONT for device/vfb/0 **********


******************* KBDFRONT for device/vkbd/0 **********


backend at /local/domain/0/backend/vkbd/11/0
/local/domain/0/backend/vkbd/11/0 connected
************************** KBDFRONT
Thread "kbdfront" exited.
backend at /local/domain/0/backend/vfb/11/0
/local/domain/0/backend/vfb/11/0 connected
"
and you use VNC to see the GRUB menu.

diff -r a24dbfcbdf69 -r 76e7d0258f65 extras/mini-os/fbfront.c
--- a/extras/mini-os/fbfront.c  Tue Jun 22 07:19:38 2010 +0100
+++ b/extras/mini-os/fbfront.c  Wed Jun 30 10:29:42 2010 -0400
@@ -124,7 +124,12 @@
     }
 
     snprintf(path, sizeof(path), "%s/state", nodename);
-    err = xenbus_switch_state(xbt, path, XenbusStateInitialised);
+    /* In the past we would have made this Initialized. But with a QEMU
+     * update 805ed3b that requires the frontend to be Connected state
+     * to progress the backend to move from InitWait to Connected.
+     * The QEMU bug fix was meant _only_ for XenFB but it affects every
+     * device. */
+    err = xenbus_switch_state(xbt, path, XenbusStateConnected);
     if (err) {
         printk("error writing initialized: %s\n", err);
         free(err);
@@ -485,7 +490,12 @@
     }
 
     snprintf(path, sizeof(path), "%s/state", nodename);
-    err = xenbus_switch_state(xbt, path, XenbusStateInitialised);
+    /* In the past we would have made this Initialized. But with a QEMU
+     * update 805ed3b that requires the frontend to be Connected state
+     * to progress the backend to move from InitWait to Connected.
+     * The QEMU bug fix was meant _only_ for XenFB but it affects every
+     * device. */
+    err = xenbus_switch_state(xbt, path, XenbusStateConnected);
     if (err) {
         message = "switching state";
         goto abort_transaction;
diff -r a24dbfcbdf69 -r 76e7d0258f65 extras/mini-os/pcifront.c
--- a/extras/mini-os/pcifront.c Tue Jun 22 07:19:38 2010 +0100
+++ b/extras/mini-os/pcifront.c Wed Jun 30 10:29:42 2010 -0400
@@ -204,7 +204,12 @@
     }
 
     snprintf(path, sizeof(path), "%s/state", nodename);
-    err = xenbus_switch_state(xbt, path, XenbusStateInitialised);
+    /* In the past we would have made this Initialized. But with a QEMU
+     * update 805ed3b that requires the frontend to be Connected state
+     * to progress the backend to move from InitWait to Connected.
+     * The QEMU bug fix was meant _only_ for XenFB but it affects every
+     * device. */
+    err = xenbus_switch_state(xbt, path, XenbusStateConnected);
     if (err) {
         message = "switching state";
         goto abort_transaction;



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