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Re: [Qemu-devel] [qemu PATCH] hw/i386/pc_sysfw: support more than one fl
From: |
Laszlo Ersek |
Subject: |
Re: [Qemu-devel] [qemu PATCH] hw/i386/pc_sysfw: support more than one flash drive |
Date: |
Wed, 27 Nov 2013 16:18:04 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20131118 Thunderbird/17.0.11 |
On 11/27/13 15:45, Markus Armbruster wrote:
> Laszlo Ersek <address@hidden> writes:
>
>> On 11/27/13 14:52, Markus Armbruster wrote:
>>> Jordan Justen <address@hidden> writes:
>>>
>>>> On Tue, Nov 26, 2013 at 5:32 AM, Laszlo Ersek <address@hidden> wrote:
>>>>> On 11/26/13 13:36, Markus Armbruster wrote:
>>>>>
>>>>>> Your stated purpose for multiple -pflash:
>>>>>>
>>>>>> 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.
>>>>>>
>>>>>> Such a split between writable part and read-only part makes sense to me.
>>>>>> How is it done in physical hardware? Single device with configurable
>>>>>> write-protect, or two separate devices?
>>>>>
>>>>> (Jordan could help more.)
>>>>>
>>>>> Likely one device that's fully writeable.
>>>>
>>>> Most parts will have a dedicated read-only line.
>>>>
>>>> Many devices have 'block-locking' that will make some subset of blocks
>>>> read-only until a reset.
>>>>
>>>> In addition to this, many chipsets will allow flash writes to be
>>>> protected by triggering SMM when a flash write occurs.
>>>>
>>>> Using multiple chips are less common due to cost, but this is not a
>>>> factor for QEMU. :)
>>>
>>> Should we stick to what real hardware does? Single device, perhaps with
>>> block locking.
>>
>> I can't back a single flash device with two drives (= two host-side
>> files), which is the incentive for this change.
>
> There's no fundamental reason why a single device model instance could
> not be backed by two block backends, named by two drive properties.
>
> I'm not claiming this is the best solution, just offering it for
> consideration.
I'll pass :) I guess in theory we could push down the multi-drive thing
to "pflash_cfi01.c". But:
- It is used by a bunch of other boards.
- Regarding i386, the second drive could automatically become (dependent
on the first drive's size) part of the range that is mirrored in
isa-bios space. Probably not intended.
- The previous point strengthens the "pflash is used by other boards
too" concern: in case of i386, I'm at least halfway aware of the
board-specific consequences of sneaking in another drive, but I have no
clue about the other boards.
- If we decide at some point to map / paste backing drives in a loop,
then the (at that time) existent device properties of pflash, let's call
them "drive0" and "drive1", will look clumsy. We'll need a way to parse
an unknown number of backend (drive) IDs. A mess.
Thanks!
Laszlo
- Re: [Qemu-devel] [qemu PATCH] hw/i386/pc_sysfw: support more than one flash drive, (continued)
- Re: [Qemu-devel] [qemu PATCH] hw/i386/pc_sysfw: support more than one flash drive, Markus Armbruster, 2013/11/22
- Re: [Qemu-devel] [qemu PATCH] hw/i386/pc_sysfw: support more than one flash drive, Laszlo Ersek, 2013/11/22
- Re: [Qemu-devel] [qemu PATCH] hw/i386/pc_sysfw: support more than one flash drive, Markus Armbruster, 2013/11/25
- Re: [Qemu-devel] [qemu PATCH] hw/i386/pc_sysfw: support more than one flash drive, Laszlo Ersek, 2013/11/25
- Re: [Qemu-devel] [qemu PATCH] hw/i386/pc_sysfw: support more than one flash drive, Markus Armbruster, 2013/11/26
- Re: [Qemu-devel] [qemu PATCH] hw/i386/pc_sysfw: support more than one flash drive, Laszlo Ersek, 2013/11/26
- Re: [Qemu-devel] [qemu PATCH] hw/i386/pc_sysfw: support more than one flash drive, Jordan Justen, 2013/11/26
- Re: [Qemu-devel] [qemu PATCH] hw/i386/pc_sysfw: support more than one flash drive, Markus Armbruster, 2013/11/27
- Re: [Qemu-devel] [qemu PATCH] hw/i386/pc_sysfw: support more than one flash drive, Laszlo Ersek, 2013/11/27
- Re: [Qemu-devel] [qemu PATCH] hw/i386/pc_sysfw: support more than one flash drive, Markus Armbruster, 2013/11/27
- Re: [Qemu-devel] [qemu PATCH] hw/i386/pc_sysfw: support more than one flash drive,
Laszlo Ersek <=
- Re: [Qemu-devel] [qemu PATCH] hw/i386/pc_sysfw: support more than one flash drive, Markus Armbruster, 2013/11/27
- Re: [Qemu-devel] [qemu PATCH] hw/i386/pc_sysfw: support more than one flash drive, Laszlo Ersek, 2013/11/27
- Re: [Qemu-devel] [qemu PATCH] hw/i386/pc_sysfw: support more than one flash drive, Markus Armbruster, 2013/11/27
- Re: [Qemu-devel] [edk2] [qemu PATCH] hw/i386/pc_sysfw: support more than one flash drive, Paolo Bonzini, 2013/11/26
- Re: [Qemu-devel] [edk2] [qemu PATCH] hw/i386/pc_sysfw: support more than one flash drive, Laszlo Ersek, 2013/11/26
- Re: [Qemu-devel] [edk2] [qemu PATCH] hw/i386/pc_sysfw: support more than one flash drive, Paolo Bonzini, 2013/11/26
- Re: [Qemu-devel] [qemu PATCH] hw/i386/pc_sysfw: support more than one flash drive, Markus Armbruster, 2013/11/26
- Re: [Qemu-devel] [qemu PATCH] hw/i386/pc_sysfw: support more than one flash drive, Laszlo Ersek, 2013/11/26
- Re: [Qemu-devel] [qemu PATCH] hw/i386/pc_sysfw: support more than one flash drive, Markus Armbruster, 2013/11/27
- Re: [Qemu-devel] [qemu PATCH] hw/i386/pc_sysfw: support more than one flash drive, Laszlo Ersek, 2013/11/27