Re: [Qemu-devel] [PATCH v4] Stop VM on ENOSPC error.

[Gleb Natapov]

On Tue, Jan 20, 2009 at 04:50:14PM +0000, Ian Jackson wrote:
> Gleb Natapov writes ("Re: [Qemu-devel] [PATCH v4] Stop VM on ENOSPC error."):
> > I would like to abolish the blocking calls from all file formats, but in
> > reality it is almost impossible. Qcow2 metadata updates is a big mess to
> > do asynchronously. The best thing we can do is to move it to another thread.
> 
> Err, I wasn't suggesting it should be done in each format in that way.
> It could be done once in block.c, before the specific format write
> method is called.
>
Before? How should we know before specific format write if there is
enough space?  And block.c is called by different file formats too. So
what do you suggest to do inside bdrv_write() function when write failed?

> So the formats would still write synchronously, and would pass errors
> up to their parent formats, until it reenters the generic block code
> where the retry would take place.  At that point the call from the
> device emulation would necessariy be asynchronous.
> 
It may reenter block formats many times during one write from ide.
Look at block-qcow2.c and calls to bdrv_pwrite() there. 

--
                        Gleb.