Re: [Qemu-devel] [Xen-devel] [PATCHv3] QEMU(upstream): Disable xen's use of O_DIRECT by default as it results in crashes.

[Alex Bligh]

Stefano,

--On 29 March 2013 17:19:26 +0000 Stefano Stabellini 
<address@hidden> wrote:

> > I think so.  blkfront reads "sectors" when QEMU moves to
> > XenbusStateConnected, in blkfront_connect.
> >
> > blk_connect is called from xen_be_try_initialise, which moves to
> > XenbusStateConnected on success.  So, QEMU's blk_connect will always be
> > called before blkfront's blkfront_connect.
>
> Alex, do you have any updates on this patch?

Sorry, I've been snowed under with other stuff.

I got to the speed bump below, then didn't get back to it after Paolo's
reply. I'll see if I can get some time tomorrow.

--
Alex Bligh

---------- Forwarded Message ----------
Date: 20 March 2013 10:26:21 +0100
From: Paolo Bonzini <address@hidden>
To: Alex Bligh <address@hidden>
CC: Stefano Stabellini <address@hidden>, George Dunlap 
<address@hidden>, Ian Campbell <address@hidden>, Ian 
Jackson <address@hidden>, address@hidden, xen-devel 
<address@hidden>, Anthony Liguori <address@hidden>
Subject: Re: [Xen-devel] [PATCHv3] QEMU(upstream): Disable xen's use of 
O_DIRECT by default as it results in crashes.

Il 20/03/2013 09:33, Alex Bligh ha scritto:
> Stefano,
>
> --On 19 March 2013 15:13:29 +0000 Stefano Stabellini
> <address@hidden> wrote:
>
> > Therefore I think that the current change is not safe, but it is pretty
> > easy to make it safe.
> > You just need to move the call to blk_open from blk_init to blk_connect.
> > Actually you can move most of blk_init to blk_connect, you just need to
> > keep the 4 xenstore_write_be_int at the end of the function.
>
> The final of these 4 writes in blk_init is:
>
>    xenstore_write_be_int(&blkdev->xendev, "sectors",
>                          blkdev->file_size / blkdev->file_blk);
>
> and blkdev->filesize comes from bdrv_getlength(blkdev->bs), and that
> requires (I think) bdrv_open to have been called. Can these
> 4 writes move safely to blk_connect? Or can we write the sectors
> count as (say) 0 here and fix it later in blk_connect? The remainder
> look ok.

I think so.  blkfront reads "sectors" when QEMU moves to
XenbusStateConnected, in blkfront_connect.

blk_connect is called from xen_be_try_initialise, which moves to
XenbusStateConnected on success.  So, QEMU's blk_connect will always be
called before blkfront's blkfront_connect.

Paolo



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