[Qemu-devel] Re: [PATCH] Seabios - read e820 table from qemu_cfg

[Jes Sorensen <Jes.Sorensen@redhat.com>]

On 01/28/10 05:39, Kevin O'Connor wrote:
> I think defining accessor functions for every piece of data passed
> through qemu-cfg interface is going to get tiring.  I'd prefer to
> extend the existing qemu-cfg "file" interface for new content.
>
> For example, add a helper with something like:
>
> int qemu_cfg_get_file(const char *name, void *dest, int maxsize);

Hi Kevin,

I think switching qemu_cfg to use a file name based interface would be
a nice feature, but I think it should be independent of this patch. I am
CC'ing Gleb on this as he did the original design I believe.

>> -    if (kvm_para_available())
>> -        // 4 pages before the bios, 3 pages for vmx tss pages, the
>> -        // other page for EPT real mode pagetable
>> -        add_e820(0xfffbc000, 4*4096, E820_RESERVED);
>> +    if (kvm_para_available()) {
>> +        u32 count;
>> +
>> +        count = qemu_cfg_e820_entries();
>> +        if (count) {
>> +            struct e820_entry entry;
>> +            int i;
>> +
>> +            for (i = 0; i<  count; i++) {
>> +                qemu_cfg_e820_load_next(&entry);
>> +                add_e820(entry.address, entry.length, entry.type);
>> +            }
>
> and then this becomes:
>
> struct e820entry map[128];
> int len = qemu_cfg_get_file("e820map",&map, sizeof(map));
> if (len>= 0)
>      for (i=0; i<len / sizeof(map[0]); i++)
>          add_e820(map[i].start, map[i].size, map[i].type);
>
> The advantage being that it should be possible to write one set of
> helper functions in both qemu and seabios that can then be used to
> pass arbitrary content.

The only issue here is that I designed the Seabios portion to not rely
on the size of the struct, to avoid having to statically reserve it like
in your example. Having the qemu_cfg_get_file() function return a
pointer to a file descriptor and then have a qemu_cfg_read() helper that
takes the descriptor as it's first argument would avoid this problem.

> As a side note, it should probably do the e820 map check even for qemu
> users (ie, not just kvm).

Ah I didn't realize Seabios would try to use the fw_cfg interface if it
wasn't running on top of QEMU. That would be good to do.

Cheers,
Jes