Re: [PATCH 08/10] scsi/scsi_bus: Add scsi_device_get

[Maxim Levitsky <mlevitsk@redhat.com>]

On Fri, 2020-09-25 at 13:26 -0400, Paolo Bonzini wrote:
> From: Maxim Levitsky <mlevitsk@redhat.com>
> 
> Add scsi_device_get which finds the scsi device
> and takes a reference to it.
> 
> Suggested-by: Stefan Hajnoczi <stefanha@gmail.com>
> Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
> Message-Id: <20200913160259.32145-8-mlevitsk@redhat.com>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
> 	Compared to Maxim's patch, I am avoiding the extra argument
> 	to do_scsi_device_find by moving the RCU_READ_LOCK_GUARD()
> 	out of do_scsi_device_find itself.
Which is a good idea, although my mindset was like, I got a device,
lets just grab a ref to it before it disappears and then do
whatever I want. The extra argument was ugly no doubt though.

Best regards,
	Maxim Levitsky

> 
>  hw/scsi/scsi-bus.c     | 11 +++++++++++
>  include/hw/scsi/scsi.h |  1 +
>  2 files changed, 12 insertions(+)
> 
> diff --git a/hw/scsi/scsi-bus.c b/hw/scsi/scsi-bus.c
> index 7599113efe..eda8cb7e70 100644
> --- a/hw/scsi/scsi-bus.c
> +++ b/hw/scsi/scsi-bus.c
> @@ -73,6 +73,17 @@ SCSIDevice *scsi_device_find(SCSIBus *bus, int channel, int id, int lun)
>      return do_scsi_device_find(bus, channel, id, lun, false);
>  }
>  
> +SCSIDevice *scsi_device_get(SCSIBus *bus, int channel, int id, int lun)
> +{
> +    SCSIDevice *d;
> +    RCU_READ_LOCK_GUARD();
> +    d = do_scsi_device_find(bus, channel, id, lun, false);
> +    if (d) {
> +        object_ref(d);
> +    }
> +    return d;
> +}
> +
>  static void scsi_device_realize(SCSIDevice *s, Error **errp)
>  {
>      SCSIDeviceClass *sc = SCSI_DEVICE_GET_CLASS(s);
> diff --git a/include/hw/scsi/scsi.h b/include/hw/scsi/scsi.h
> index 7a55cdbd74..09fa5c9d2a 100644
> --- a/include/hw/scsi/scsi.h
> +++ b/include/hw/scsi/scsi.h
> @@ -190,6 +190,7 @@ int scsi_device_get_sense(SCSIDevice *dev, uint8_t *buf, int len, bool fixed);
>  int scsi_SG_IO_FROM_DEV(BlockBackend *blk, uint8_t *cmd, uint8_t cmd_size,
>                          uint8_t *buf, uint8_t buf_size);
>  SCSIDevice *scsi_device_find(SCSIBus *bus, int channel, int target, int lun);
> +SCSIDevice *scsi_device_get(SCSIBus *bus, int channel, int target, int lun);
>  
>  /* scsi-generic.c. */
>  extern const SCSIReqOps scsi_generic_req_ops;