[Qemu-devel] [PATCH] block: do not probe zero-sized disks

[Qemu-devel] [PATCH] block: do not probe zero-sized disks

[Paolo Bonzini]

A blank CD or DVD is visible as a zero-sized disks.  Probing such
disks will lead to an EIO and a failure to start the VM.  Treating
them as raw is a better solution.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 block.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/block.c b/block.c
index c05875f..b9da10e 100644
--- a/block.c
+++ b/block.c
@@ -532,7 +532,7 @@ static int find_image_format(const char *filename, BlockDriver **pdrv)
     }
 
     /* Return the raw BlockDriver * to scsi-generic devices or empty drives */
-    if (bs->sg || !bdrv_is_inserted(bs)) {
+    if (bs->sg || !bdrv_is_inserted(bs) || bdrv_getlength(bs) == 0) {
         bdrv_delete(bs);
         drv = bdrv_find_format("raw");
         if (!drv) {
-- 
1.8.1

Re: [Qemu-devel] [PATCH] block: do not probe zero-sized disks

[Kevin Wolf]

Am 10.01.2013 15:39, schrieb Paolo Bonzini:
> A blank CD or DVD is visible as a zero-sized disks.  Probing such
> disks will lead to an EIO and a failure to start the VM.  Treating
> them as raw is a better solution.
> 
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  block.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/block.c b/block.c
> index c05875f..b9da10e 100644
> --- a/block.c
> +++ b/block.c
> @@ -532,7 +532,7 @@ static int find_image_format(const char *filename, BlockDriver **pdrv)
>      }
>  
>      /* Return the raw BlockDriver * to scsi-generic devices or empty drives */
> -    if (bs->sg || !bdrv_is_inserted(bs)) {
> +    if (bs->sg || !bdrv_is_inserted(bs) || bdrv_getlength(bs) == 0) {
>          bdrv_delete(bs);
>          drv = bdrv_find_format("raw");
>          if (!drv) {
> 

Thanks, rebased and applied to the block branch.

Kevin

Re: [Qemu-devel] [PATCH] block: do not probe zero-sized disks

[Eric Blake]

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On 01/10/2013 07:39 AM, Paolo Bonzini wrote:
> A blank CD or DVD is visible as a zero-sized disks.  Probing such
> disks will lead to an EIO and a failure to start the VM.  Treating
> them as raw is a better solution.
> 
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  block.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/block.c b/block.c
> index c05875f..b9da10e 100644
> --- a/block.c
> +++ b/block.c
> @@ -532,7 +532,7 @@ static int find_image_format(const char *filename, BlockDriver **pdrv)
>      }
>  
>      /* Return the raw BlockDriver * to scsi-generic devices or empty drives */
> -    if (bs->sg || !bdrv_is_inserted(bs)) {
> +    if (bs->sg || !bdrv_is_inserted(bs) || bdrv_getlength(bs) == 0) {

Do we need to extend this to all files with size smaller than the length
of the header used in probing to determine a non-raw file?  Or is the
case of someone passing a 1-byte file as a backing file of a device too
unlikely, where refusing to start the VM is okay for that case?

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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Re: [Qemu-devel] [PATCH] block: do not probe zero-sized disks

[Stefan Hajnoczi]

On Thu, Jan 10, 2013 at 03:39:27PM +0100, Paolo Bonzini wrote:
> A blank CD or DVD is visible as a zero-sized disks.  Probing such
> disks will lead to an EIO and a failure to start the VM.  Treating
> them as raw is a better solution.
> 
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  block.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/block.c b/block.c
> index c05875f..b9da10e 100644
> --- a/block.c
> +++ b/block.c
> @@ -532,7 +532,7 @@ static int find_image_format(const char *filename, BlockDriver **pdrv)
>      }
>  
>      /* Return the raw BlockDriver * to scsi-generic devices or empty drives */
> -    if (bs->sg || !bdrv_is_inserted(bs)) {
> +    if (bs->sg || !bdrv_is_inserted(bs) || bdrv_getlength(bs) == 0) {

Looks good but I wouldn't understand the reason for the zero size check
when reading the code.  Please add a comment so no one changes/removes
this code in the future.

Stefan