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Re: [Qemu-devel] [PATCH] NVMe: Initial commit to add an NVM Express devi


From: Busch, Keith
Subject: Re: [Qemu-devel] [PATCH] NVMe: Initial commit to add an NVM Express device
Date: Thu, 13 Dec 2012 00:13:46 +0000

On Mon, Dec 10, 2012 at 7:11 AM, Stefan Hajnoczi <address@hidden> wrote:
> Quick pointers to get started on Kevin's suggestion:
>
> bdrv_aio_readv(), bdrv_aio_writev(), bdrv_aio_flush(), and
> bdrv_aio_discard() provide the block device operations that emulated
> storage controllers use.

There seems to be an issue with the bdrv_aio_[readv/writev] routines. I added 
some additional tracing in the block and coroutine code, and well, long story 
short, the coroutine "bdrv_co_io_em" needs to call "qemu_coroutine_yield" 
before his aio callback "bdrv_co_io_em_complete" invokes 
"qemu_coroutine_enter". It does not always win this race in my experiments, and 
qemu aborts with a recursive re-entry error. I don't know this coroutine code 
well enough to propose a fix -- I'd say maybe use locks but I think that 
defeats the purpose of using coroutines if I understand them correctly?



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