Re: [Xen-devel] [RFC PATCH V3 1/2] xen: pass kernel initrd to qemu

[Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>]

Chunyan Liu writes ("[RFC PATCH V3 1/2] xen: pass kernel initrd to qemu"):
> xen side patch to support xen HVM direct kernel boot:
> support 'kernel', 'ramdisk', 'cmdline' (and 'root', 'extra' as well
> which would be deprecated later) in HVM config file, parse config file,
> pass -kernel, -initrd, -append parameters to qemu.
...
> +Currently, direct kernel boot can be supported by PV guests, and HVM guests
> +with limitations. For HVM guests, in case of stubdom-dm and old rombios,
> +direct kernel boot is not supported.

What does "PV guests" mean here ?  Do you mean guest kernels which
support the Xen PV environment ?

If so, what is the benefit of booting them "direct" but HVM, rather
than simply booting them PV ?

>  =item B<bootloader="PROGRAM">
>  
>  Run C<PROGRAM> to find the kernel image and ramdisk to use.  Normally
>  C<PROGRAM> would be C<pygrub>, which is an emulation of
> -grub/grub2/syslinux.
> +grub/grub2/syslinux. Either B<kernel> or B<bootloader> must be specified
> +for PV guests.

Surely using this should be possible for direct kernel boot too.

> +/*
> + * LIBXL_HAVE_BUILDINFO_HVM_DIRECT_KERNEL_BOOT
> + *
> + * If this is defined, then the libxl_domain_build_info structure will
> + * contain hvm.kernel, hvm.cmdline and hvm.ramdisk. hvm.kernel is a string
> + * to indicate kernel image location, hvm.ramdisk is a string to indicate
> + * ramdisk location, hvm.cmdline is a string to indicate the paramters which
> + * would be appened to kernel image.

If we are going to do this then I think the kernel, cmdline and
ramdisk (and bootloader) parameters shoudl be moved into the main part
of the domain_build_info struct.  This will involve a compatibility
layer: temporarily (for at least one release) both will be supported
so the IDL will have to have both and code inside libxl will have to
honour either.

The #define should then be
  LIBXL_HAVE_BUILD_INFO_CMDLINE
or some such - because all libxl callers will want to update to the
  new API eventually.

> +static char *parse_cmdline(XLU_Config *config)
> +{
> +    char *cmdline = NULL;
> +    const char *root = NULL, *extra = NULL, *buf = NULL;
> +
> +    xlu_cfg_get_string (config, "cmdline", &buf, 0);
> +    xlu_cfg_get_string (config, "root", &root, 0);
> +    xlu_cfg_get_string (config, "extra", &extra, 0);
> +
> +    if (buf) {
> +        cmdline = strdup(buf);
> +        if (root || extra)
> +            fprintf(stderr, "Warning: ignoring deprecated root= and extra= "
> +                    "in favour of cmdline=\n");

Why are you deprecating root= and extra= ?

They seem likely to be a useful distinction if we decide to add
further default options in the future.

If you do want to deprecate them, you should make this very clear -
probably by putting that change in a separate patch in your series.

Thanks,
Ian.

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