[dm-devel] [PATCH v3 2/5] scsi_dh: add scsi_dh_attached_handler_name

[Moger, Babu]

I have tested these patches(1 to 5) with scsi_dh_rdac and scsi_dh_alua. These modules
are loaded as part of initrd image. For some devices scsi_dh_rdac is the default and 
for some scsi_dh_alua is default.  Everything worked as expected.

Output of dmsetup table

3600a0b8000501df0000008134b432748: 0 41943040 multipath 2 queue_if_no_path default_hw_handler 1 rdac 2 1 round-robin 0 1 1 66:0 6 round-robin 0 1 1 8:64 1
360080e50001b098200008f054f63c73c: 0 20971520 multipath 2 queue_if_no_path default_hw_handler 1 alua 2 1 round-robin 0 1 1 67:80 14 round-robin 0 1 1 67:160 9


> -----Original Message-----
> From: Mike Snitzer [mailto:snitzer at redhat.com]
> Sent: Thursday, May 10, 2012 9:11 AM
> To: Christoph Hellwig
> Cc: linux-scsi at vger.kernel.org; agk at redhat.com; hare at suse.de; Moger,
> Babu; sekharan at us.ibm.com
> Subject: Re: [PATCH v3 2/5] scsi_dh: add scsi_dh_attached_handler_name
> 
> On Thu, May 10 2012 at  2:55am -0400,
> Christoph Hellwig <hch at infradead.org> wrote:
> 
> > On Wed, May 09, 2012 at 09:12:46PM -0400, Mike Snitzer wrote:
> > > Originally posted to dm-devel but Chandra reminded me to post to
> > > linux-scsi for James to pick it up.
> > >
> > > -------8<-------
> > >
> > > Introduce scsi_dh_attached_handler_name() to retrieve the name of the
> > > scsi_dh that is attached to the scsi_device associated with the provided
> > > request queue.  Returns NULL if a scsi_dh is not attached.
> > >
> > > Also, fix scsi_dh_{attach,detach} function header comments to
> document
> > > @q rather than @sdev.
> >
> > Wha'ts the use case for this?
> 
> See this patch:
> http://www.redhat.com/archives/dm-devel/2012-May/msg00046.html
> 
> (I attributed this change to Hannes because it was based on his earlier
> patch... I should probably change that given that in the end I
> re-wrote/merged his patch with my earlier patch...)
> 
> Anyway, DM mpath doesn't want to know about the "scsi_dh" structure, but
> we need the name of the attached handler (to adjust the multipath
> device's 'hw_handler_name' and to get an additional ref on the attached
> scsi_dh via dm-mapth.c:parse_path's scsi_dh_attach).
> 
> BTW, only reason I split the scsi_dh change from the above dm-mpath
> patch is because I'm patching SCSI and DM and need to send the changes
> through different trees.
> 
> > The name is stale as soon as the function returns.
> 
> Yeah, I have since wondered about that myself.  In practice the attached
> handler should remain attached so the name really won't be stale.
> 
> But in theory there could be a race with scsi_dh_detach.  So I think the
> following should address your concern?
> 
> If so I'll refresh and repost the appropriate patches.
> 
> Thanks.
> 
> diff --git a/drivers/md/dm-mpath.c b/drivers/md/dm-mpath.c
> index 1039e7f..6f11956 100644
> --- a/drivers/md/dm-mpath.c
> +++ b/drivers/md/dm-mpath.c
> @@ -592,10 +592,11 @@ static struct pgpath *parse_path(struct dm_arg_set
> *as, struct path_selector *ps
>  		q = bdev_get_queue(p->path.dev->bdev);
> 
>  	if (m->use_default_hw_handler) {
> -		const char *attached_handler_name =
> scsi_dh_attached_handler_name(q);
> +		const char *attached_handler_name =
> +			scsi_dh_attached_handler_name(q, GFP_KERNEL);
>  		if (attached_handler_name) {
>  			kfree(m->hw_handler_name);
> -			m->hw_handler_name =
> kstrdup(attached_handler_name, GFP_KERNEL);
> +			m->hw_handler_name = attached_handler_name;
>  		}
>  	}
> 
> diff --git a/drivers/scsi/device_handler/scsi_dh.c
> b/drivers/scsi/device_handler/scsi_dh.c
> index 83071e4..33e422e 100644
> --- a/drivers/scsi/device_handler/scsi_dh.c
> +++ b/drivers/scsi/device_handler/scsi_dh.c
> @@ -533,10 +533,12 @@ EXPORT_SYMBOL_GPL(scsi_dh_detach);
>   * scsi_dh_attached_handler_name - Get attached device handler's name
>   * @q - Request queue that is associated with the scsi_device
>   *      that may have a device handler attached
> + * @gfp - the GFP mask used in the kmalloc() call when allocating memory
>   *
>   * Returns name of attached handler, NULL if no handler is attached.
> + * Caller must take care to free the returned string.
>   */
> -const char *scsi_dh_attached_handler_name(struct request_queue *q)
> +const char *scsi_dh_attached_handler_name(struct request_queue *q,
> gfp_t gfp)
>  {
>  	unsigned long flags;
>  	struct scsi_device *sdev;
> @@ -552,7 +554,7 @@ const char *scsi_dh_attached_handler_name(struct
> request_queue *q)
>  		return NULL;
> 
>  	if (sdev->scsi_dh_data)
> -		handler_name = sdev->scsi_dh_data->scsi_dh->name;
> +		handler_name = kstrdup(sdev->scsi_dh_data->scsi_dh-
> >name, gfp);
> 
>  	put_device(&sdev->sdev_gendev);
>  	return handler_name;
> diff --git a/include/scsi/scsi_dh.h b/include/scsi/scsi_dh.h
> index 94f502b..620c723 100644
> --- a/include/scsi/scsi_dh.h
> +++ b/include/scsi/scsi_dh.h
> @@ -60,7 +60,7 @@ extern int scsi_dh_activate(struct request_queue *,
> activate_complete, void *);
>  extern int scsi_dh_handler_exist(const char *);
>  extern int scsi_dh_attach(struct request_queue *, const char *);
>  extern void scsi_dh_detach(struct request_queue *);
> -extern const char *scsi_dh_attached_handler_name(struct request_queue
> *q);
> +extern const char *scsi_dh_attached_handler_name(struct request_queue
> *, gfp_t);
>  extern int scsi_dh_set_params(struct request_queue *, const char *);
>  #else
>  static inline int scsi_dh_activate(struct request_queue *req,
> @@ -81,7 +81,8 @@ static inline void scsi_dh_detach(struct request_queue
> *q)
>  {
>  	return;
>  }
> -static inline const char *scsi_dh_attached_handler_name(struct
> request_queue *q)
> +static inline const char *scsi_dh_attached_handler_name(struct
> request_queue *q,
> +							gfp_t gfp)
>  {
>  	return NULL;
>  }
> 
>