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

Chris Boot
2012-02-11T12:26:29Z

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