Re: [Qemu-devel] [qemu PATCH] hw/i386/pc_sysfw: support more than one flash drive

[Laszlo Ersek <lersek@redhat.com>]

On 11/22/13 13:21, Markus Armbruster wrote:
> Laszlo Ersek <lersek@redhat.com> writes:
> 
>> This patch allows the user to usefully specify
>>
>>   -drive file=img_1,if=pflash,format=raw,readonly \
>>   -drive file=img_2,if=pflash,format=raw
>>
>> on the command line. The flash images will be mapped under 4G in their
>> reverse unit order -- that is, with their base addresses progressing
>> downwards, in increasing unit order.
>>
>> (The unit number increases with command line order if not explicitly
>> specified.)
>>
>> This accommodates the following use case: suppose that OVMF is split in
>> two parts, a writeable host file for non-volatile variable storage, and a
>> read-only part for bootstrap and decompressible executable code.
>>
>> The binary code part would be read-only, centrally managed on the host
>> system, and passed in as unit 0. The variable store would be writeable,
>> VM-specific, and passed in as unit 1.
>>
>>   00000000ffe00000-00000000ffe1ffff (prio 0, R-): system.flash1
>>   00000000ffe20000-00000000ffffffff (prio 0, R-): system.flash0
>>
>> (If the guest tries to write to the flash range that is backed by the
>> read-only drive, bdrv_write() in pflash_update() will correctly deny the
>> write with -EACCES, and pflash_update() won't care, which suits us well.)
> 
> Before this patch:
> 
> You can define as many if=pflash drives as you want.  Any with non-zero
> index are silently ignored.
> 
> If you don't specify one with index=0, you get a ROM at the top of the
> 32 bit address space, contents taken from -bios (default "bios.bin").
> Up to its last 128KiB are aliased at the top of the ISA address space.
> 
> If you do specify one with index=0, you get a pflash device at the top
> of the 32 bit address space, with contents from the drive, and -bios is
> silently ignored.  Up to its last 128KiB are copied to a ROM at the top
> of the (20 bit) ISA address space.
> 
> After this patch (please correct misunderstandings):
> 
> Now the drives after the first unused index are silently ignored.
> 
> If you don't specify one with index=0, no change.
> 
> If you do, you now get N pflash devices, where N is the first unused
> index.  Each pflash's contents is taken from the respective drive.  The
> flashes are mapped at the top of the 32 bit address space in reverse
> index order.  -bios is silently ignored, as before.  Up to the last
> 128KiB of the index=0 flash are copied to a ROM at the top of the ISA
> address space.
> 
> Thus, no change for index=0.  For index=1..N, we now get additional
> flash devices.
> 
> Correct?

Yes.

Thanks
Laszlo