Re: [Qemu-devel] [PATCH v2] iscsi: Refuse to open as writable if the LUN is write protected

[Peter Lieven]

On 30.10.2014 13:09, Paolo Bonzini wrote:
> On 10/30/2014 12:43 PM, Peter Lieven wrote:
> > On 30.10.2014 12:23, 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>
> > > ---
> > > v2: Improve error message.
> > >       Fall back to a warning if mode sense failed.
> > >       Check unmarshal return value.
> > > ---
> > >    block/iscsi.c | 46 ++++++++++++++++++++++++++++++++++++++++++++++
> > >    1 file changed, 46 insertions(+)
> > >
> > > diff --git a/block/iscsi.c b/block/iscsi.c
> > > index 233f462..dcacbca 100644
> > > --- a/block/iscsi.c
> > > +++ b/block/iscsi.c
> > > @@ -1219,6 +1219,44 @@ static void
> > > iscsi_attach_aio_context(BlockDriverState *bs,
> > >                  qemu_clock_get_ms(QEMU_CLOCK_REALTIME) + NOP_INTERVAL);
> > >    }
> > >    +static bool iscsi_is_write_protected(IscsiLun *iscsilun)
> > > +{
> > > +    struct scsi_task *task;
> > > +    struct scsi_mode_sense *ms = NULL;
> > > +
> > > +    task = iscsi_modesense6_sync(iscsilun->iscsi, iscsilun->lun,
> > > +            1, SCSI_MODESENSE_PC_CURRENT,
> > > +            0x3F,
> > > +            0, 255);
> > > +
> > > +    if (task == NULL) {
> > > +        error_report("Failed to send MODE_SENSE6 command: %s",
> > > +                     iscsi_get_error(iscsilun->iscsi));
> > > +        goto out;
> > > +    }
> > > +
> > > +    if (task->status != SCSI_STATUS_GOOD) {
> > > +        error_report("MODE_SENSE6 failed: %s",
> > > +                     iscsi_get_error(iscsilun->iscsi));
> > > +        goto out;
> > > +    }
> > > +    ms = scsi_datain_unmarshall(task);
> > > +    if (!ms) {
> > > +        error_report("MODE_SENSE6 failed: %s",
> > > +                     iscsi_get_error(iscsilun->iscsi));
> > > +        goto out;
> > > +    }
> > > +out:
> > > +    if (task) {
> > > +        scsi_free_scsi_task(task);
> > > +    }
> > > +    if (!ms) {
> > ms points to freed memory after scsi_free_scsi_task.
> > furthermore the requests likely fails with task->status != SCSI_STATUS_GOOD
> > if the modesense implementation is broken etc.
> This is a mix of your and Fam's code.  Looks good?
>
> static bool iscsi_is_write_protected(IscsiLun *iscsilun)
> {
>      struct scsi_task *task;
>      struct scsi_mode_sense *ms = NULL;
>      bool wrprotected = false;
>
>      task = iscsi_modesense6_sync(iscsilun->iscsi, iscsilun->lun,
>                                   1, SCSI_MODESENSE_PC_CURRENT,
>                                   0x3F, 0, 255);
>      if (task == NULL) {
>          error_report("Failed to send MODE_SENSE(6) command: %s",
>                       iscsi_get_error(iscsilun->iscsi));
>          goto out;
>      }
>
>      if (task->status != SCSI_STATUS_GOOD) {
>          error_report("MODE_SENSE(6) failed: %s",
>                       iscsi_get_error(iscsilun->iscsi));
>          goto out;
>      }
>      ms = scsi_datain_unmarshall(task);
>      if (!ms) {
>          error_report("Failed to unmarshall MODE_SENSE(6) data: %s",
>                       iscsi_get_error(iscsilun->iscsi));
>          goto out;
>      }
>      wrprotected = ms->device_specific_parameter & 0x80;
>
> out:
>      if (task) {
>          scsi_free_scsi_task(task);
>      }
>      return wrprotected;
> }

i would add the prefix "iSCSI: " to the error_reports as we
have it for other outputs. (noticed this after writing my mail).

Otherwise looks good.

Reviewed-by: Peter Lieven <address@hidden>

and actually also

Tested-by: Peter Lieven <address@hidden>

Peter