[Qemu-devel] [Bug 1825207] [NEW] fw_cfg_machine_reset destroys user bootorder setting

[Mark Eichin]

Public bug reported:

Demonstrated against 2.11 (ubuntu bionic 1:2.11+dfsg-1ubuntu7.12) and
3.1 (as built under bionic from the 1:3.1+dfsg-2ubuntu3 source package)
although the code hasn't changed between them and github master also
appears to have this same code branch.

What I was trying to do: select a boot disk using `-fw_cfg
name=bootorder,string=/address@hidden/address@hidden based on the qemu and 
seabios
documentation.  (Why do I want to do that? using qemu for installer
testing for a specific kind of real machine and need to match the bios
boot order.)

What happened instead: same search-based boot order that I get without
that option.  Also, /sys/firmware/qemu_fw_cfg/by_name/bootorder/raw is
empty and .../size is "0".

Brutal work around that did a useful thing:

--- qemu-3.1+dfsg.orig/hw/nvram/fw_cfg.c
+++ qemu-3.1+dfsg/hw/nvram/fw_cfg.c
@@ -869,8 +869,10 @@ static void fw_cfg_machine_reset(void *o
     FWCfgState *s = opaque;
     char *bootindex = get_boot_devices_list(&len);
 
+#if 0
     ptr = fw_cfg_modify_file(s, "bootorder", (uint8_t *)bootindex, len);
     g_free(ptr);
+#endif
 }

This change allowed the boot to work (so my bootorder setting was making
it to seabios) and also showed up explicitly in
/sys/firmware/qemu_fw_cfg.

I don't know if fw_cfg_modify_file is intended to append rather than
replace, but it doesn't; based on the seabios "Runtime_config" docs
which suggest "look at the Searching bootorder for output and paste that
into the bootorder file" I'd instead just have it only fill in bootorder
if there's *no* existing setting, since a user can read out the defaults
and copy them in as described if they want the fallback, but that's just
from my interpretation of the docs.

** Affects: qemu
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/1825207

Title:
  fw_cfg_machine_reset destroys user bootorder setting

Status in QEMU:
  New

Bug description:
  Demonstrated against 2.11 (ubuntu bionic 1:2.11+dfsg-1ubuntu7.12) and
  3.1 (as built under bionic from the 1:3.1+dfsg-2ubuntu3 source
  package) although the code hasn't changed between them and github
  master also appears to have this same code branch.

  What I was trying to do: select a boot disk using `-fw_cfg
  name=bootorder,string=/address@hidden/address@hidden based on the qemu and 
seabios
  documentation.  (Why do I want to do that? using qemu for installer
  testing for a specific kind of real machine and need to match the bios
  boot order.)

  What happened instead: same search-based boot order that I get without
  that option.  Also, /sys/firmware/qemu_fw_cfg/by_name/bootorder/raw is
  empty and .../size is "0".

  Brutal work around that did a useful thing:

  --- qemu-3.1+dfsg.orig/hw/nvram/fw_cfg.c
  +++ qemu-3.1+dfsg/hw/nvram/fw_cfg.c
  @@ -869,8 +869,10 @@ static void fw_cfg_machine_reset(void *o
       FWCfgState *s = opaque;
       char *bootindex = get_boot_devices_list(&len);
   
  +#if 0
       ptr = fw_cfg_modify_file(s, "bootorder", (uint8_t *)bootindex, len);
       g_free(ptr);
  +#endif
   }

  This change allowed the boot to work (so my bootorder setting was
  making it to seabios) and also showed up explicitly in
  /sys/firmware/qemu_fw_cfg.

  I don't know if fw_cfg_modify_file is intended to append rather than
  replace, but it doesn't; based on the seabios "Runtime_config" docs
  which suggest "look at the Searching bootorder for output and paste
  that into the bootorder file" I'd instead just have it only fill in
  bootorder if there's *no* existing setting, since a user can read out
  the defaults and copy them in as described if they want the fallback,
  but that's just from my interpretation of the docs.

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