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Re: [Qemu-block] [PATCH 3/4] ide: add support for cancelable read reques
From: |
Peter Lieven |
Subject: |
Re: [Qemu-block] [PATCH 3/4] ide: add support for cancelable read requests |
Date: |
Wed, 28 Oct 2015 20:56:53 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.4.0 |
Am 28.10.2015 um 12:26 schrieb Stefan Hajnoczi:
> On Tue, Oct 27, 2015 at 11:58:55AM +0100, Peter Lieven wrote:
>> Am 26.10.2015 um 11:39 schrieb Stefan Hajnoczi:
>>> On Mon, Oct 12, 2015 at 02:27:24PM +0200, Peter Lieven wrote:
>>>> +BlockAIOCB *ide_readv_cancelable(IDEState *s, int64_t sector_num,
>>>> + QEMUIOVector *iov, int nb_sectors,
>>>> + BlockCompletionFunc *cb, void *opaque)
>>>> +{
>>>> + BlockAIOCB *aioreq;
>>>> + IDECancelableRequest *req;
>>>> + int c = 0;
>>>> +
>>>> + QLIST_FOREACH(req, &s->cancelable_requests, list) {
>>>> + c++;
>>>> + }
>>>> + if (c > MAX_CANCELABLE_REQS) {
>>>> + return NULL;
>>>> + }
>>> A BH is probably needed here to schedule an cb(-EIO) call since this
>>> function isn't supposed to return NULL if it's a direct replacement for
>>> blk_aio_readv().
>> You mean sth like:
>>
>> acb = qemu_aio_get(&bdrv_em_aiocb_info, bs, cb, opaque);
>> acb->bh = aio_bh_new(bdrv_get_aio_context(bs), bdrv_aio_bh_cb, acb);
>> acb->ret = -EIO;
>> qemu_bh_schedule(acb->bh);
>>
>> return &acb->common;
> Yes.
>
>> As pointed out in my comment to your requestion about write/discard I think
>> it should
>> be feasible to use buffered readv requests for all read-only IDE devices.
>> Only thing I'm unsure about is reopening. A reopen seems to only flush the
>> device not
>> drain all requests.
> bdrv_reopen_prepare() callers should drain requests. For example,
> bdrv_reopen_multiple() (and indirectly bdrv_reopen()) call
> bdrv_drain_all(). Is this what you mean?
Yes, I have only found a flush in bdrv_reopen_prepare, but if you say they need
to drain before
I think it is safe to use the buffered_ide_readv for all read-only IDE devices
not only CDROMs.
Peter
- Re: [Qemu-block] [PATCH 2/4] ide/atapi: blk_aio_readv may return NULL, (continued)
Re: [Qemu-block] [PATCH V2 0/4] ide: avoid main-loop hang on CDROM/NFS failure, Stefan Hajnoczi, 2015/10/26