linux-kernel - Re: [PATCH 2/3] firewire-sbp2: Ignore SBP-2 targets on the local node

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Message-ID: <20120211122832.25f00d59@stein>
Date:	Sat, 11 Feb 2012 12:28:32 +0100
From:	Stefan Richter <stefanr@...6.in-berlin.de>
To:	Chris Boot <bootc@...tc.net>
Cc:	linux1394-devel@...ts.sourceforge.net,
	linux-kernel@...r.kernel.org, Greg KH <gregkh@...uxfoundation.org>
Subject: Re: [PATCH 2/3] firewire-sbp2: Ignore SBP-2 targets on the local
 node

On Feb 10 Chris Boot wrote:
> The firewire-sbp2 module tries to login to an SBP-2/3 target even when
> it is running on the local node, which fails because of the inability to
> fetch data from DMA mapped regions using firewire transactions on the
> local node. It also doesn't make much sense to have the initiator and
> target on the same node, so this patch prevents this behaviour.
> 
> Signed-off-by: Chris Boot <bootc@...tc.net>
> Cc: Stefan Richter <stefanr@...6.in-berlin.de>
> ---
>  drivers/firewire/sbp2.c |   19 +++++++++++++++++--
>  1 files changed, 17 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/firewire/sbp2.c b/drivers/firewire/sbp2.c
> index ed5bbbf..1572a79 100644
> --- a/drivers/firewire/sbp2.c
> +++ b/drivers/firewire/sbp2.c
> @@ -1138,6 +1138,12 @@ static int sbp2_probe(struct device *dev)
>  	struct Scsi_Host *shost;
>  	u32 model, firmware_revision;
>  
> +	/* ignore targets on the local node */
> +	if (device->node == device->card->local_node) {
> +		dev_set_drvdata(&unit->device, NULL);
> +		return 0;
> +	}
> +
>  	if (dma_get_max_seg_size(device->card->device) > SBP2_MAX_SEG_SIZE)
>  		BUG_ON(dma_set_max_seg_size(device->card->device,
>  					    SBP2_MAX_SEG_SIZE));
> @@ -1204,6 +1210,10 @@ static void sbp2_update(struct fw_unit *unit)
>  	struct sbp2_target *tgt = dev_get_drvdata(&unit->device);
>  	struct sbp2_logical_unit *lu;
>  
> +	/* no drvdata means a target on a local node; ignoring */
> +	if (!tgt)
> +		return;
> +
>  	fw_device_enable_phys_dma(fw_parent_device(unit));
>  
>  	/*
> @@ -1223,10 +1233,15 @@ static int sbp2_remove(struct device *dev)
>  	struct fw_device *device = fw_parent_device(unit);
>  	struct sbp2_target *tgt = dev_get_drvdata(&unit->device);
>  	struct sbp2_logical_unit *lu, *next;
> -	struct Scsi_Host *shost =
> -		container_of((void *)tgt, struct Scsi_Host, hostdata[0]);
> +	struct Scsi_Host *shost;
>  	struct scsi_device *sdev;
>  
> +	/* no drvdata means a target on a local node; ignoring */
> +	if (!tgt)
> +		return 0;
> +
> +	shost = container_of((void *)tgt, struct Scsi_Host, hostdata[0]);
> +
>  	/* prevent deadlocks */
>  	sbp2_unblock(tgt);
>  

In the long run, we might want to support target and initiator set up to
reside on the same node and talking to each other via loopback, if
somebody really needs it and if it can be done with reasonably little
effort.  Until then, the patch is fine with me WRT what it accomplishes.

But I do wonder:  Shouldn't this be implemented by returning from the
driver probe method with an error?  If so, which errno should be
returned?  (Cc'ing driver core maintainer for this question.)
-- 
Stefan Richter
-=====-===-- --=- -=-==
http://arcgraph.de/sr/
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