Re: [Qemu-devel] [PATCH 1/2] iscsi: Use bs->sg for everything else than disks

["Benoît Canet" <benoit.canet@irqsave.net>]

The Wednesday 05 Mar 2014 à 16:00:48 (+0100), Kevin Wolf wrote :
> The current iscsi block driver code makes the rather arbitrary decision
> that TYPE_MEDIUM_CHANGER and TYPE_TAPE devices have bs->sg = 1 and all
> other device types are disks.
> 
> Instead of this, check for TYPE_DISK to expose the disk interface and
> make everything else bs->sg = 1. In particular, this includes devices
> with TYPE_STORAGE_ARRAY, which is what LUN 0 of an iscsi target is.
> (See https://bugzilla.redhat.com/show_bug.cgi?id=1067784 for the exact
> scenario.)
> 
> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> ---
>  block/iscsi.c | 9 ++++-----
>  1 file changed, 4 insertions(+), 5 deletions(-)
> 
> diff --git a/block/iscsi.c b/block/iscsi.c
> index 0a15f53..b490e98 100644
> --- a/block/iscsi.c
> +++ b/block/iscsi.c
> @@ -1231,12 +1231,11 @@ static int iscsi_open(BlockDriverState *bs, QDict *options, int flags,
>      bs->total_sectors = sector_lun2qemu(iscsilun->num_blocks, iscsilun);
>      bs->request_alignment = iscsilun->block_size;
>  
> -    /* Medium changer or tape. We dont have any emulation for this so this must
> -     * be sg ioctl compatible. We force it to be sg, otherwise qemu will try
> -     * to read from the device to guess the image format.
> +    /* We don't have any emulation for devices other than disks and CD-ROMs, so
> +     * this must be sg ioctl compatible. We force it to be sg, otherwise qemu
> +     * will try to read from the device to guess the image format.
>       */
> -    if (iscsilun->type == TYPE_MEDIUM_CHANGER ||
> -        iscsilun->type == TYPE_TAPE) {
> +    if (iscsilun->type != TYPE_DISK && iscsilun->type != TYPE_ROM) {
I don't understand you are talking about type TYPE_STORAGE_ARRAY in the commit
message but testing against TYPE_ROM and they are not the same.
Maybe a comment explaining the role of TYPE_ROM would give a clue to non scsi
savy persons like me.

Best regards

Benoît

>          bs->sg = 1;
>      }
>  
> -- 
> 1.8.1.4
> 
>