Re: [Qemu-devel] [PATCH] iscsi: Refuse to open as writable if the LUN is write protected

[Paolo Bonzini]

On 10/29/2014 02:13 PM, Fam Zheng wrote:
> Before, when a write protected iSCSI target is attached as scsi-disk
> with BDRV_O_RDWR, we report it as writable, while in fact all writes
> will fail.
> 
> One way to improve this is to report write protect flag as true to
> guest, but a even better way is to refuse using a write protected LUN to
> guest.
> 
> Target write protect flag is checked with a mode sense query.
> 
> Signed-off-by: Fam Zheng <address@hidden>
> ---
>  block/iscsi.c | 30 ++++++++++++++++++++++++++++++
>  1 file changed, 30 insertions(+)
> 
> diff --git a/block/iscsi.c b/block/iscsi.c
> index 233f462..c154928 100644
> --- a/block/iscsi.c
> +++ b/block/iscsi.c
> @@ -1339,6 +1339,36 @@ static int iscsi_open(BlockDriverState *bs, QDict 
> *options, int flags,
>      scsi_free_scsi_task(task);
>      task = NULL;
>  
> +    /* Check the write protect flag of the LUN if we want to write */
> +    if (flags & BDRV_O_RDWR) {
> +        struct scsi_mode_sense *ms;
> +
> +        task = iscsi_modesense6_sync(iscsilun->iscsi, iscsilun->lun,
> +                                      1, SCSI_MODESENSE_PC_CURRENT,
> +                                      0x3F,
> +                                      0, 255);
> +
> +        if (task == NULL) {
> +            error_setg(errp, "Failed to send MODE_SENSE10 command: %s\n",

This is MODE SENSE(6).  Fixed and applied.

Paolo

> +                       iscsi_get_error(iscsilun->iscsi));
> +            ret = -EINVAL;
> +            goto out;
> +        }
> +
> +        if (task->status != SCSI_STATUS_GOOD) {
> +            error_setg(errp, "MODE_SENSE10 failed: %s\n",
> +                       iscsi_get_error(iscsi));
> +            ret = -EINVAL;
> +            goto out;
> +        }
> +        ms = scsi_datain_unmarshall(task);
> +        if (ms->device_specific_parameter & 0x80) {
> +            error_setg(errp, "Cannot open a write protected LUN as 
> read-write");
> +            ret = -EPERM;
> +            goto out;
> +        }
> +    }
> +
>      iscsi_readcapacity_sync(iscsilun, &local_err);
>      if (local_err != NULL) {
>          error_propagate(errp, local_err);
>