Re: [PATCH 1/3] firewire-sbp2: Take into account Unit_Unique_ID

Re: [PATCH 1/3] firewire-sbp2: Take into account Unit_Unique_ID

[Stefan Richter]

On Feb 10 Chris Boot wrote:
> If the target's unit directory contains a Unit_Unique_ID entry, we
> should use that as the target's GUID for identification purposes. The
> SBP-2 standards document says:
> 
> "Although the node unique ID (EUI-64) present in the bus information
> block is sufficient to uniquely identify nodes attached to Serial Bus,
> it is insufficient to identify a target when a vendor implements a
> device with multiple Serial Bus node connections. In this case initiator
> software requires information by which a particular target may be
> uniquely identified, regardless of the Serial Bus access path used."
> 
> [ IEEE T10 P1155D Revision 4, Section 7.6 (page 51) ] and
> [ IEEE T10 P1467D Revision 5, Section 7.9 (page 74) ]
> 
> Signed-off-by: Chris Boot <bootc@bootc.net>
> Cc: Stefan Richter <stefanr@s5r6.in-berlin.de>
> ---
>  drivers/firewire/sbp2.c |   17 +++++++++++++++++
>  1 files changed, 17 insertions(+), 0 deletions(-)
> 
> diff --git a/drivers/firewire/sbp2.c b/drivers/firewire/sbp2.c
> index 80e95aa..ed5bbbf 100644
> --- a/drivers/firewire/sbp2.c
> +++ b/drivers/firewire/sbp2.c
> @@ -211,6 +211,7 @@ static struct fw_device *target_device(struct sbp2_target *tgt)
>  #define SBP2_CSR_UNIT_CHARACTERISTICS	0x3a
>  #define SBP2_CSR_FIRMWARE_REVISION	0x3c
>  #define SBP2_CSR_LOGICAL_UNIT_NUMBER	0x14
> +#define SBP2_CSR_UNIT_UNIQUE_ID		0x8d
>  #define SBP2_CSR_LOGICAL_UNIT_DIRECTORY	0xd4
>  
>  /* Management orb opcodes */
> @@ -997,6 +998,17 @@ static int sbp2_add_logical_unit(struct sbp2_target *tgt, int lun_entry)
>  	return 0;
>  }
>  
> +static int sbp2_get_unit_unique_id(struct sbp2_target *tgt,
> +				    const u32 *leaf)
> +{
> +	if ((leaf[0] & 0xffff0000) != 0x00020000)
> +		return -EINVAL;

This could be relaxed to "if (leaf[0] < 0x00020000)", but the stricter
check is fine too.

> +
> +	tgt->guid = (u64)leaf[1] << 32 | leaf[2];
> +
> +	return 0;
> +}
> +
>  static int sbp2_scan_logical_unit_dir(struct sbp2_target *tgt,
>  				      const u32 *directory)
>  {
> @@ -1048,6 +1060,11 @@ static int sbp2_scan_unit_dir(struct sbp2_target *tgt, const u32 *directory,
>  				return -ENOMEM;
>  			break;
>  
> +		case SBP2_CSR_UNIT_UNIQUE_ID:
> +			if (sbp2_get_unit_unique_id(tgt, ci.p - 1 + value) < 0)
> +				return -EINVAL;
> +			break;
> +
>  		case SBP2_CSR_LOGICAL_UNIT_DIRECTORY:
>  			/* Adjust for the increment in the iterator */
>  			if (sbp2_scan_logical_unit_dir(tgt, ci.p - 1 + value) < 0)

The error return here is wrong.  Garbage in a non-essential part of the
Config ROM is no reason to refuse to work with a device.  It is too common
for firmware to have various bogus values in there.  For instance, we
never check the CRC of a Config ROM block because wrongly calculated CRCs
or even zero CRC is quite commonly seen with otherwise correct Config ROMs.

And there is another problem with the patch:  In fringe cases, we might
now create more than one scsi_device instances with the same ieee1394_id
sysfs attribute value.  Those cases are:
 1. There are two targets present which expose the same, hence non-unique
    and thus standards-violating Unit_Unique_ID. Or
 2. There is a single target connected through more than one link, it has
    got a Unit_Unique_ID, and either
     2.a  it accepts concurrent login despite firewire-sbp2 demanding an
          exclusive login (which is its default mode), or
     2.b  firewire-sbp2 is configured to work in concurrent login mode and
          the target grants concurrent logins.

We do not need to care for case 1.  It cannot be distinguished from case
2, and we already do not care for the case that there are two or more
nodes with a non-unique Node_Unique_ID.  Devices with the latter bug exist
but are rare, judging from historical discussion on linux1394-devel.

Case 2.a is highly unlikely, and I think we should not worry about that
either.

Should we do something about case 2.b?  Where in the Linux SCSI
initiator stack is multipathing handled --- in transport layer drivers or
higher up?  (Cc'ing LSML for this question.)
-- 
Stefan Richter
-=====-===-- --=- -=-==
http://arcgraph.de/sr/

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Re: [PATCH 1/3] firewire-sbp2: Take into account Unit_Unique_ID

[Chris Boot]

On 11/02/2012 11:12, Stefan Richter wrote:
> On Feb 10 Chris Boot wrote:
>> If the target's unit directory contains a Unit_Unique_ID entry, we
>> should use that as the target's GUID for identification purposes. The
>> SBP-2 standards document says:
>>
>> "Although the node unique ID (EUI-64) present in the bus information
>> block is sufficient to uniquely identify nodes attached to Serial Bus,
>> it is insufficient to identify a target when a vendor implements a
>> device with multiple Serial Bus node connections. In this case initiator
>> software requires information by which a particular target may be
>> uniquely identified, regardless of the Serial Bus access path used."
>>
>> [ IEEE T10 P1155D Revision 4, Section 7.6 (page 51) ] and
>> [ IEEE T10 P1467D Revision 5, Section 7.9 (page 74) ]
>>
>> Signed-off-by: Chris Boot<bootc@bootc.net>
>> Cc: Stefan Richter<stefanr@s5r6.in-berlin.de>
>> ---
>>   drivers/firewire/sbp2.c |   17 +++++++++++++++++
>>   1 files changed, 17 insertions(+), 0 deletions(-)
>>
>> diff --git a/drivers/firewire/sbp2.c b/drivers/firewire/sbp2.c
>> index 80e95aa..ed5bbbf 100644
>> --- a/drivers/firewire/sbp2.c
>> +++ b/drivers/firewire/sbp2.c
>> @@ -211,6 +211,7 @@ static struct fw_device *target_device(struct sbp2_target *tgt)
>>   #define SBP2_CSR_UNIT_CHARACTERISTICS	0x3a
>>   #define SBP2_CSR_FIRMWARE_REVISION	0x3c
>>   #define SBP2_CSR_LOGICAL_UNIT_NUMBER	0x14
>> +#define SBP2_CSR_UNIT_UNIQUE_ID		0x8d
>>   #define SBP2_CSR_LOGICAL_UNIT_DIRECTORY	0xd4
>>
>>   /* Management orb opcodes */
>> @@ -997,6 +998,17 @@ static int sbp2_add_logical_unit(struct sbp2_target *tgt, int lun_entry)
>>   	return 0;
>>   }
>>
>> +static int sbp2_get_unit_unique_id(struct sbp2_target *tgt,
>> +				    const u32 *leaf)
>> +{
>> +	if ((leaf[0]&  0xffff0000) != 0x00020000)
>> +		return -EINVAL;
>
> This could be relaxed to "if (leaf[0]<  0x00020000)", but the stricter
> check is fine too.

Well the standard does say the length must be exactly 2 rather than just 
defining it a leaf node that contains an EUI-64. But I did not realise 
various firmware gets things quite so wrong sometimes...

>> +
>> +	tgt->guid = (u64)leaf[1]<<  32 | leaf[2];
>> +
>> +	return 0;
>> +}
>> +
>>   static int sbp2_scan_logical_unit_dir(struct sbp2_target *tgt,
>>   				      const u32 *directory)
>>   {
>> @@ -1048,6 +1060,11 @@ static int sbp2_scan_unit_dir(struct sbp2_target *tgt, const u32 *directory,
>>   				return -ENOMEM;
>>   			break;
>>
>> +		case SBP2_CSR_UNIT_UNIQUE_ID:
>> +			if (sbp2_get_unit_unique_id(tgt, ci.p - 1 + value)<  0)
>> +				return -EINVAL;
>> +			break;
>> +
>>   		case SBP2_CSR_LOGICAL_UNIT_DIRECTORY:
>>   			/* Adjust for the increment in the iterator */
>>   			if (sbp2_scan_logical_unit_dir(tgt, ci.p - 1 + value)<  0)
>
> The error return here is wrong.  Garbage in a non-essential part of the
> Config ROM is no reason to refuse to work with a device.  It is too common
> for firmware to have various bogus values in there.  For instance, we
> never check the CRC of a Config ROM block because wrongly calculated CRCs
> or even zero CRC is quite commonly seen with otherwise correct Config ROMs.

Wow. I didn't expect things to get so bad. :-( I guess in this case we 
simply ignore the return value, which would have the effect of not 
setting the GUID.

> And there is another problem with the patch:  In fringe cases, we might
> now create more than one scsi_device instances with the same ieee1394_id
> sysfs attribute value.   Those cases are:
>   1. There are two targets present which expose the same, hence non-unique
>      and thus standards-violating Unit_Unique_ID. Or
>   2. There is a single target connected through more than one link, it has
>      got a Unit_Unique_ID, and either
>       2.a  it accepts concurrent login despite firewire-sbp2 demanding an
>            exclusive login (which is its default mode), or
>       2.b  firewire-sbp2 is configured to work in concurrent login mode and
>            the target grants concurrent logins.
>
> We do not need to care for case 1.  It cannot be distinguished from case
> 2, and we already do not care for the case that there are two or more
> nodes with a non-unique Node_Unique_ID.  Devices with the latter bug exist
> but are rare, judging from historical discussion on linux1394-devel.
>
> Case 2.a is highly unlikely, and I think we should not worry about that
> either.
>
> Should we do something about case 2.b?  Where in the Linux SCSI
> initiator stack is multipathing handled --- in transport layer drivers or
> higher up?  (Cc'ing LSML for this question.)

I believe multipathing is handled by multipathd, which uses devmapper to 
handle the actual data flow. Multipathd itself works out which LUNs it 
can see over multiple paths (using multiple /dev/sdX devices) and just 
creates the devmapper mappings as necessary. I'm not even convinced 
multipathd would care about the SBP-2 target port identifier, preferring 
instead to use the WWN on the LUN.

HTH,
Chris

-- 
Chris Boot
bootc@bootc.net

Re: [PATCH 1/3] firewire-sbp2: Take into account Unit_Unique_ID

[Stefan Richter]

On Feb 11 Chris Boot wrote:
> On 11/02/2012 11:12, Stefan Richter wrote:
> > On Feb 10 Chris Boot wrote:
> >> +	if ((leaf[0]&  0xffff0000) != 0x00020000)
> >> +		return -EINVAL;
> >
> > This could be relaxed to "if (leaf[0]<  0x00020000)", but the stricter
> > check is fine too.
> 
> Well the standard does say the length must be exactly 2 rather than just 
> defining it a leaf node that contains an EUI-64. But I did not realise 
> various firmware gets things quite so wrong sometimes...

I expect firmware writers to get length == 2 right, but we need to
protect ourselves against very dumb mistakes or malicious input of course.

Whether the length field is 2 or not could be totally ignored by
firewire-sbp2 just like we ignore the block CRC, except that we need to
catch the corner case of a bogus Config ROM where the descriptor leaf
overlaps the 1 kB ROM size limit, or that it is placed right at the end of
the ROM but is shorter than 2 quadlets.

core-device.c::read_config_rom() already catches the cases of blocks
overlapping the end of the ROM but merely handles them by overwriting the
block length by 0.  Higher-level code which reads a descriptor block or
directory block in the Config ROM cache is required to respect the length
field of the block.  We could simplify this for upper layer code by
overwriting the pointer to the block instead of the header of the block,
like it is done already with pointers to blocks outside of the ROM.

Anyway; if the length of an alleged EUI-64 descriptor leaf is greater than
2, I agree that there is little reason to look at the rest of the
descriptor; it would likely contain garbage too.
-- 
Stefan Richter
-=====-===-- --=- -=-==
http://arcgraph.de/sr/