Re: [Qemu-devel] [PATCH v2 4/5] console: pass Monitor to vga_hw_screen_dump/hw_vga_dump

[Daniel P. Berrange]

On Wed, Mar 14, 2012 at 03:14:10PM +0200, Alon Levy wrote:
> On Wed, Mar 14, 2012 at 09:32:58AM -0300, Luiz Capitulino wrote:
> > On Wed, 14 Mar 2012 08:37:13 +0000
> > "Daniel P. Berrange" <address@hidden> wrote:
> > 
> > > > First, with this applied you will not know the size in advance.  Also
> > > > one of the approaches discussed is to allow passing in a file handle.
> > > > That is a possible way to handle async screendumps too: just write to
> > > > the passed file handle and close it when done.  Obvious drawback is that
> > > > this will not cover the classic way of specifying the output filename as
> > > > argument.
> > 
> > As Daniel explains below, this is not a drawback and there's no problem
> > supporting multiple ways of returning the image.
> > 
> > The real drawback of making this w/o async support is that you can't detect
> > errors.
> > 
> 
> You also can't detect when the writing is done (unless you continuously
> try to parse the file yourself..)

That's one of the nice benefits of using a pipe - you'll just get EOF
when reading from it, when QEMU is done.

> 
> > > This would not be a problem from libvirt's POV - we don't really want a
> > > file on disk anyway, nor do we want to pull the whole image into memory.
> > > Our ideal approach is to just have an pipe FD with QEMU, which we just
> > > incrementally read image data from, and forward to the client app via
> > > a libvirt stream object.

Daniel
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