Re: [Qemu-devel] when to bdrv_co_flush()?

[Stefan Hajnoczi]

On Mon, Nov 10, 2014 at 12:41:45PM +0800, lihuiba wrote:
> bdrv_co_flush() will flush all cached data to persistent storage, and I'm
> wondering whether guest sync() will eventually trigger bdrv_co_flush() be
> called. 

virtio-blk and other emulated storage controllers use bdrv_aio_flush()
to implement disk write cache flush commands.

> Intuitively, guest sync() should trigger bdrv_co_flush() in qemu. But simple
> 
> grep gave me a negative answer. So I'm wondering why it's not like what I
> 
> suspected.

A correctly configured guest will send cache flush commands, and a
correctly configured QEMU will honor them.

If want help finding the answer, please provide details:
1. Your QEMU command-line
2. Your guest OS version and file system mount options
3. Why you believe bdrv_co_flush() is not being called

Stefan

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