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Date: Fri, 11 Feb 2011 13:49:06 +0100
From: Kevin Wolf <kwolf@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH] xen_disk: cope with missing xenstore "params"
	node
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To: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Cc: qemu-devel@nongnu.org

Am 11.02.2011 13:38, schrieb Stefano Stabellini:
> When disk is a cdrom and the drive is empty the "params" node in
> xenstore might be missing completely: cope with it instead of
> segfaulting.
> 
> Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
> 
> 
> diff --git a/hw/xen_disk.c b/hw/xen_disk.c
> index 134ac33..e553c4c 100644
> --- a/hw/xen_disk.c
> +++ b/hw/xen_disk.c
> @@ -577,12 +577,13 @@ static int blk_init(struct XenDevice *xendev)
>  {
>      struct XenBlkDev *blkdev = container_of(xendev, struct XenBlkDev, xendev);
>      int index, qflags, have_barriers, info = 0;
> -    char *h;
> +    char *h = NULL;
>  
>      /* read xenstore entries */
>      if (blkdev->params == NULL) {
>  	blkdev->params = xenstore_read_be_str(&blkdev->xendev, "params");
> -        h = strchr(blkdev->params, ':');
> +        if (blkdev->params != NULL)
> +            h = strchr(blkdev->params, ':');

The coding style requires braces here.

>  	if (h != NULL) {
>  	    blkdev->fileproto = blkdev->params;
>  	    blkdev->filename  = h+1;

Let me add some more context:

    if (h != NULL) {
        blkdev->fileproto = blkdev->params;
        blkdev->filename  = h+1;
        *h = 0;
    } else {
        blkdev->fileproto = "<unset>";
        blkdev->filename  = blkdev->params;
    }

So in the NULL case we now have blkdev->filename = NULL. Doesn't this
just move the crash a few lines downwards when bdrv_open() tries to use
NULL as its filename?

Kevin