Re: [Xen-devel] [PATCH RFC] libxl: make firmware_override able to cope with relative path

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 08/08/16 16:49, Ian Jackson wrote:
> Wei Liu writes ("Re: [PATCH RFC] libxl: make firmware_override able to cope 
> with relative path"):
>> On Mon, Aug 08, 2016 at 04:09:49PM +0100, Ian Jackson wrote:
>>> Wei Liu writes ("[PATCH RFC] libxl: make firmware_override able to cope 
>>> with relative path"):
>>>> And also document that option in xl.cfg(5).
>>> ...
>>>> -Select the virtual firmware that is exposed to the guest.
>>>> +Select the virtual bios that is exposed to the guest.
>>>>  By default, a guess is made based on the device model, but sometimes
>>>>  it may be useful to request a different one, like UEFI.
>>> hvmloader is surely not a `virtual bios' for two reasons: one is that
>>> technically something like UEFI firmware is not a bios.  The other is
>>> that hvmloader is responsible for doing some other stuff too, AIUI ?
>> This section is for bios=. I think it is better to not use "firmware" to
>> describe bios in the context of Xen. It's easy to confuse this with
>> firmware_override.
> Oh!  Yes, right, of course.
>
>> Yes, I agree.
>>
>> How about we decide that libxl will search for files in the following
>> order if the string is not an absolute path:
>>
>> 1. current working directory
>> 2. Xen specific directory (case by case, if applicable)
>>
>> And then we document, for each xl.cfg option, the search path. Also we
>> encourage people to use absolute path for consistent results.
> SGTM.
>
> I wonder if we should be able to specify to libxl to "please don't use
> relative paths" (or even "relative paths are relative to this
> specified location").  libxl might be embedded in another program
> whose cwd can't be adjusted and shouldn't be relied on.

The important bit which XTF and regular users want is relative to the
.cfg file, rather than $CWD.

Imagine your files are layed out like:

dir/
dir/vm1/vm1.cfg,vm1-kernel,vm1-ramdisk
dir/vm2/vm2.cfg,vm2-kernel,vm2-ramdisk

In this case, it would be natural to use relative paths in vm1.cfg, with
no path components even.

For kernel and ramdisks, `xl create` can use $CWD, /etc/xen/, or an
absolute address
For firmware_override, `xl create` is relative to the ./configure
$(libexecdir), or an absolute address

What XTF wants to use is

xl create tests/foo/foo.cfg

with foo.cfg referring to kernels or firmware_overrides in the same
directory.

~Andrew

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