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Re: [Qemu-devel] [PATCH v2 0/3] SysFS driver for QEMU fw_cfg device
From: |
Christopher Covington |
Subject: |
Re: [Qemu-devel] [PATCH v2 0/3] SysFS driver for QEMU fw_cfg device |
Date: |
Wed, 26 Aug 2015 14:15:03 -0400 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:36.0) Gecko/20100101 Thunderbird/36.0 |
Hi Gabriel,
On 08/19/2015 04:49 PM, Gabriel L. Somlo wrote:
> Hi Ard,
>
> On Wed, Aug 19, 2015 at 11:42:02AM +0200, Ard Biesheuvel wrote:
>> (missed some cc's)
>>
>> On 19 August 2015 at 11:38, Ard Biesheuvel <address@hidden> wrote:
>>> From: "Gabriel L. Somlo" <address@hidden>
>>>> Several different architectures supported by QEMU are set up with a
>>>> "firmware configuration" (fw_cfg) device, used to pass configuration
>>>> "blobs" into the guest by the host running QEMU.
>>>>
>>>> Historically, these config blobs were mostly of interest to the guest
>>>> BIOS, but since QEMU v2.4 it is possible to insert arbitrary blobs via
>>>> the command line, which makes them potentially interesting to userspace
>>>> (e.g. for passing early boot environment variables, etc.).
>>>>
>>>
>>> Does 'potentially interesting' mean you have a use case? Could you
>>> elaborate?
>
> My personal one would be something like:
>
> cat > guestinfo.txt << EOT
> KEY1="val1"
> KEY2="val2"
> ...
> EOT
>
> qemu-system-x86_64 ... -fw-cfg name="opt/guestinfo",file=./guestinfo.txt ...
>
> Then, from inside the guest:
>
> . /sys/firmware/qemu_fw_cfg/by_name/opt/guestinfo/raw
>
> do_something_with $KEY1 $KEY2
> ...
>
> But I'm thinking this is only one of the many positive things one
> could do with the ability to access random host-supplied blobs from
> guest userspace :)
I do this with kernel parameters:
host:
qemu-system-aarch64 -append="KEY1=val1 KEY2=val2"
guest:
KEY1=`sed -nr s/.*KEY1=([^ ]+).*/\1/ /proc/cmdline`
KEY2=`sed -nr s/.*KEY2=([^ ]+).*/\1/ /proc/cmdline`
do_something_with $KEY1 $KEY2
In practice it's just script=hostfile, where hostfile is available to the
guest via a 9P passthrough filesystem mount.
While quite architecture specific, I've also previously used an
"angel-cmdline" tool for similar purposes. Peter's recent semihosting patches
support such a tool for AArch64. (On AArch32 upstream QEMU disallows
semihosting from userspace.)
Before I had 9P on all the simulators I regularly ran, I used a semihosting
based "angel-load" tool.
Regards,
Christopher Covington
--
Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
a Linux Foundation Collaborative Project
- [Qemu-devel] [PATCH v2 0/3] SysFS driver for QEMU fw_cfg device, Gabriel L. Somlo, 2015/08/11
- [Qemu-devel] [PATCH v2 3/3] firmware: fw_cfg: create directory hierarchy for fw_cfg file names, Gabriel L. Somlo, 2015/08/11
- [Qemu-devel] [PATCH v2 2/3] kobject: export kset_find_obj() to be used from modules, Gabriel L. Somlo, 2015/08/11
- [Qemu-devel] [PATCH v2 1/3] firmware: introduce sysfs driver for QEMU's fw_cfg device, Gabriel L. Somlo, 2015/08/11
- Message not available
- Re: [Qemu-devel] [PATCH v2 0/3] SysFS driver for QEMU fw_cfg device, Ard Biesheuvel, 2015/08/19
- Re: [Qemu-devel] [PATCH v2 0/3] SysFS driver for QEMU fw_cfg device, Gabriel L. Somlo, 2015/08/19
- Re: [Qemu-devel] [PATCH v2 0/3] SysFS driver for QEMU fw_cfg device, Leif Lindholm, 2015/08/19
- Re: [Qemu-devel] [PATCH v2 0/3] SysFS driver for QEMU fw_cfg device, Ard Biesheuvel, 2015/08/20
- Re: [Qemu-devel] [PATCH v2 0/3] SysFS driver for QEMU fw_cfg device, Gabriel L. Somlo, 2015/08/20
- Re: [Qemu-devel] [PATCH v2 0/3] SysFS driver for QEMU fw_cfg device, Ard Biesheuvel, 2015/08/24
- Re: [Qemu-devel] [PATCH v2 0/3] SysFS driver for QEMU fw_cfg device,
Christopher Covington <=