Re: [PATCH 1/5] hw/smbios: support loading OEM strings values from a file

[Daniel P . Berrangé]

On Wed, Sep 09, 2020 at 10:18:47AM +0200, Laszlo Ersek wrote:
> On 09/08/20 18:54, Daniel P. Berrangé wrote:
> > Some applications want to pass quite large values for the OEM strings
> > entries. Rather than having huge strings on the command line, it would
> > be better to load them from a file, as supported with -fw_cfg.
> > 
> > This introduces the "valuefile" parameter allowing for:
> > 
> >   $ echo -n "thisthing" > mydata.txt
> >   $ qemu-system-x86_64 \
> >     -smbios type=11,value=something \
> >     -smbios type=11,valuefile=mydata.txt \
> >     -smbios type=11,value=somemore \
> >     ...other args...
> > 
> > Now in the guest
> > 
> > $ dmidecide -t 11
> > Getting SMBIOS data from sysfs.
> > SMBIOS 2.8 present.
> > 
> > Handle 0x0E00, DMI type 11, 5 bytes
> > OEM Strings
> >     String 1: something
> >     String 2: thisthing
> >     String 3: somemore
> > 
> > Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
> > ---
> >  hw/smbios/smbios.c | 72 +++++++++++++++++++++++++++++++++++++---------
> >  1 file changed, 59 insertions(+), 13 deletions(-)
> 
> (gearing up to test this / look into the edk2 problem, just one question
> in passing: could we / would we simplify this with g_file_get_contents()?)

BTW, to test this, I'm doing the following.

See the attached 'make-tiny-initrd.py' script. It expects "busybox" on
the host OS and builds a tiny initrd containing busybox.

It can optionally copy in arbitrary other commands, and shared libraries
they link to.  By default it will launch an interactive shell in the
guest, but you can tell it to run a specific command, after which it
will poweroff.

I want to run dmidecode, so I'm using

 $ make-tiny-image.py --run "dmidecode" dmidecode

which both copies dmidecode into the initrd, and also runs it by
default.

It creates 'tiny-initrd.img'

Then I simply boot the host OS kernel using this initrd.


  ./build/qemu-system-x86_64  \
      -kernel /boot/vmlinuz-5.7.14-200.fc32.x86_64 \
      -initrd tiny-initrd.img
      -append 'console=ttyS0'
      -m 1000
      -serial stdio
      -display none
      -blockdev 
'{"driver":"file","filename":"/usr/share/OVMF/OVMF_CODE.fd","node-name":"libvirt-pflash0-storage","auto-read-only":true,"discard":"unmap"}'
      -blockdev 
'{"node-name":"libvirt-pflash0-format","read-only":true,"driver":"raw","file":"libvirt-pflash0-storage"}'
      -blockdev 
'{"driver":"file","filename":"/home/berrange/src/virt/qemu/OVMF_VARS.fd","node-name":"libvirt-pflash1-storage","auto-read-only":true,"discard":"unmap"}'
      -blockdev 
'{"node-name":"libvirt-pflash1-format","read-only":false,"driver":"raw","file":"libvirt-pflash1-storage"}'
      -machine 
pc-q35-4.0,accel=kvm,usb=off,smm=on,dump-guest-core=off,pflash0=libvirt-pflash0-format,pflash1=libvirt-pflash1-format,smbios-ep=3_0
      -chardev file,path=firmware.log,id=firmwarelog
      -device isa-debugcon,iobase=0x402,chardev=firmwarelog
      -smbios type=11,path=smallfile.txt


I have a file 'bigfile.txt' that contains 14 MB of plain text.

I then create 'smallfile.txt' from this

  $ dd if=bigfile.txt of=littlefile.txt bs=1 count=130863

If count=130863 or smaller than EDK2 succesfully boots the guest.

If count=130864 or larger then AFAICT it gets stuck in EDK2 or
very early boot - the guest OS never runs.

If smbios-ep=2_1 (or is omitted), then the size limit is smaller of course
but QEMU validates that for you.

Regards,
Daniel
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make-tiny-image.py
Description: Text document