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Re: [Qemu-devel] [RFC] block-trace Low Level Command Supporting Disk Int
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] [RFC] block-trace Low Level Command Supporting Disk Introspection |
Date: |
Wed, 15 May 2013 10:25:00 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130311 Thunderbird/17.0.4 |
Il 15/05/2013 09:59, Kevin Wolf ha scritto:
>>> Do you mean you'd model the 'active' mode after 'block-backup,' or actually
>>> call functions provided by 'block-backup'?
>>
>> No, I'll just reuse the same hooks within block/mirror.c (almost... it
>> looks like I need after_write too, not just before_write :( that's a
>> pity).
>
> Makes me wonder if using a real BlockDriver for the filter from the
> beginning wouldn't be better than accumulating more and more hooks and
> having to find ways to pass data from 'before' to 'after' hooks...
We don't need a way to pass data from before to after hooks, a simple
scan of a linked list will do.
>> Basically:
>>
>> 1) before the write, if there is space in the job's buffers, allocate a
>> MirrorOp and a data buffer for the write. Also record whether the block
>> was dirty before;
>>
>> 2) after the write, do nothing if there was no room to allocate the data
>> buffer. Else clear the block from the dirty bitmap. If the block was
>> dirty, read the whole cluster from the source as in passive mirroring.
>> If it wasn't, copy the data from guest memory to the preallocated buffer
>> and write it to the destination;
>
> Does the "if there was no room" part mean that the mirror is active only
> sometimes?
Yes, otherwise the guest can allocate arbitrary amounts of memory in the
host just by starting a few very large I/O operations.
> And why even bother with a dirty bitmap for an active mirror? The
> background job that sequentially processes the whole image only needs a
> counter, no bitmap.
That's not enough for the case when the host crashes and you have to
restart the mirroring or complete it offline.
Paolo
> At which point it looks like implementing it separate from mirror.c
> could make more sense.
>
> Kevin
>
- [Qemu-devel] [RFC] block-trace Low Level Command Supporting Disk Introspection, Wolfgang Richter, 2013/05/13
- Re: [Qemu-devel] [RFC] block-trace Low Level Command Supporting Disk Introspection, Stefan Hajnoczi, 2013/05/14
- Re: [Qemu-devel] [RFC] block-trace Low Level Command Supporting Disk Introspection, Kevin Wolf, 2013/05/14
- Re: [Qemu-devel] [RFC] block-trace Low Level Command Supporting Disk Introspection, Paolo Bonzini, 2013/05/14
- Re: [Qemu-devel] [RFC] block-trace Low Level Command Supporting Disk Introspection, Wolfgang Richter, 2013/05/14
- Re: [Qemu-devel] [RFC] block-trace Low Level Command Supporting Disk Introspection, Paolo Bonzini, 2013/05/14
- Re: [Qemu-devel] [RFC] block-trace Low Level Command Supporting Disk Introspection, Wolfgang Richter, 2013/05/14
- Re: [Qemu-devel] [RFC] block-trace Low Level Command Supporting Disk Introspection, Kevin Wolf, 2013/05/15
- Re: [Qemu-devel] [RFC] block-trace Low Level Command Supporting Disk Introspection,
Paolo Bonzini <=
- Re: [Qemu-devel] [RFC] block-trace Low Level Command Supporting Disk Introspection, Kevin Wolf, 2013/05/15
- Re: [Qemu-devel] [RFC] block-trace Low Level Command Supporting Disk Introspection, Paolo Bonzini, 2013/05/15
- Re: [Qemu-devel] [RFC] block-trace Low Level Command Supporting Disk Introspection, Kevin Wolf, 2013/05/15
- Re: [Qemu-devel] [RFC] block-trace Low Level Command Supporting Disk Introspection, Paolo Bonzini, 2013/05/15
- Re: [Qemu-devel] [RFC] block-trace Low Level Command Supporting Disk Introspection, Wolfgang Richter, 2013/05/22
Re: [Qemu-devel] [RFC] block-trace Low Level Command Supporting Disk Introspection, Wolfgang Richter, 2013/05/14
Re: [Qemu-devel] [RFC] block-trace Low Level Command Supporting Disk Introspection, Richard W.M. Jones, 2013/05/16