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Re: [Qemu-devel] Re: block: format vs. protocol, and how they stack
From: |
Markus Armbruster |
Subject: |
Re: [Qemu-devel] Re: block: format vs. protocol, and how they stack |
Date: |
Tue, 22 Jun 2010 16:24:21 +0200 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/23.1 (gnu/linux) |
Kevin Wolf <address@hidden> writes:
> Am 21.06.2010 18:21, schrieb Markus Armbruster:
>> Christoph Hellwig <address@hidden> writes:
>>
[...]
>>> The user basically can specify two things:
>>>
>>> - a transport protocol. Normally this is just the filesystem
>>> interface, but it can also be nbd, http or for really sick people
>>> vvfat. This is a setting which can't be guessed, btw - it needs
>>> to be explicitly set in some way, with file used as a reasonable
>>> fallback.
>>>
>>> - an image format. This one interprets the content the transport
>>> protocol delivers to us. This can either be raw for not interpreting
>>> it all, or things like qcow2 / vmdk to add more functionality to it.
>>
>> You describe the special case where format and protocol make some sense:
>> you have a block driver that can transport bits in arbitrary formats,
>> and a block driver that interprets bits without caring for transport.
>
> No, that's not a special case. It's the only case there is.
>
>> In the general case, we have things like vvfat that make people wonder
>> whether it's a format or a protocol. You can't stack it onto a
>> transport, so it can't be a format! You can't stack a format on it, so
>> it can't be a protocol!
>
> Sure you can stack formats on it. raw and blkdebug are the ones that
> will be happy with the data that vvfat provides.
You can stack raw and blkdebug on *anything*. And that includes qcow2.
Does that make qcow2 a protocol? Are we running in circles yet? :)
I've come the conclusion that distinguishing between format and protocol
doesn't help. It only breeds confusion (and e-mail, lots of e-mail).
I've rethought blockdev_add, and I think I can do quite well without
format and protocol. Let me try that in practice. I'll post revised
docs & code when I have them.
- [Qemu-devel] Re: block: format vs. protocol, and how they stack, (continued)
- [Qemu-devel] Re: block: format vs. protocol, and how they stack, Anthony Liguori, 2010/06/21
- [Qemu-devel] Re: block: format vs. protocol, and how they stack, Anthony Liguori, 2010/06/21
- Re: [Qemu-devel] Re: block: format vs. protocol, and how they stack, Christoph Hellwig, 2010/06/21
- Re: [Qemu-devel] Re: block: format vs. protocol, and how they stack, Paul Brook, 2010/06/21
- Re: [Qemu-devel] Re: block: format vs. protocol, and how they stack, Anthony Liguori, 2010/06/21
- Re: [Qemu-devel] Re: block: format vs. protocol, and how they stack, Christoph Hellwig, 2010/06/21
- Re: [Qemu-devel] Re: block: format vs. protocol, and how they stack, Anthony Liguori, 2010/06/21
- Re: [Qemu-devel] Re: block: format vs. protocol, and how they stack, Markus Armbruster, 2010/06/21
- Re: [Qemu-devel] Re: block: format vs. protocol, and how they stack, Markus Armbruster, 2010/06/21
- Re: [Qemu-devel] Re: block: format vs. protocol, and how they stack, Kevin Wolf, 2010/06/22
- Re: [Qemu-devel] Re: block: format vs. protocol, and how they stack,
Markus Armbruster <=
- Re: [Qemu-devel] Re: block: format vs. protocol, and how they stack, Christoph Hellwig, 2010/06/28
- Re: [Qemu-devel] Re: block: format vs. protocol, and how they stack, Jamie Lokier, 2010/06/22
- [Qemu-devel] Re: block: format vs. protocol, and how they stack, Anthony Liguori, 2010/06/21
- [Qemu-devel] Re: block: format vs. protocol, and how they stack, Kevin Wolf, 2010/06/22
- [Qemu-devel] Re: block: format vs. protocol, and how they stack, Anthony Liguori, 2010/06/22
- [Qemu-devel] Re: block: format vs. protocol, and how they stack, Kevin Wolf, 2010/06/22
- [Qemu-devel] Re: block: format vs. protocol, and how they stack, Anthony Liguori, 2010/06/22
- [Qemu-devel] Re: block: format vs. protocol, and how they stack, Markus Armbruster, 2010/06/21
- [Qemu-devel] Re: block: format vs. protocol, and how they stack, Kevin Wolf, 2010/06/22
- Re: [Qemu-devel] Re: block: format vs. protocol, and how they stack, Jamie Lokier, 2010/06/22