On 20/07/09 01:47 PM, Garrett D'Amore wrote: > Darren Reed wrote: >> Garrett D'Amore wrote: >>> Darren Reed wrote: >>>> The current design of mac_header_info() and its accompanying structure >>>> suggest that when it comes to the MAC header, a variable sized one, >>>> where >>>> each packet may have a different MAC header length, was planned for. >>>> >>>> >>>> However the current implementation runs counter to that: all of the >>>> MAC >>>> types currently set the header length to a constant, which some may >>>> consider >>>> to be a bug for ethernet as it would always exclude the VLAN header >>>> if that >>>> were present. >>>> >>>> However, if we aren't going to implement per-packet variation of MAC >>>> header sizes, then doesn't it make sense to have the header length >>>> also be >>>> a property of the MAC provider itself, rather than just a packet? >>>> i.e. to >>>> have a mac_header_len() that is modeled after mac_addr_len(). >>>> >>>> Is anyone aware of any MAC layer devices that are likely to run on >>>> Solaris that would have a variable size MAC header? >>> >>> I've seen devices where the MAC header was dependent on the type of >>> packet -- anycast used one length, and unicast another. (Don't >>> remember what the protocol, possibly ATM or HIPPI.) >> >> So nothing likely to actually run on Solaris :) > > Do we know if IPoIB has a fixed header length?
Well, the mac_ib module behaves like it is fixed. >>> The other thing is that there is work on things like RBridges, plus >>> the VLAN protocols, to embed additional information into the headers >>> and extend the header length. >> >> Both of which would at least have a "minimum" length, yes? > > What do you mean by "minimum"? That the MAC header will always be at least X bytes long, but otherwise, one can't be sure. >> >> Should mac_header_len() return sizeof(struct ether_header) for >> packets with the VLAN header intact? >> Or would that be a bug? > > I don't know... I suspect its a bug, but that might depend on how the > client is used. I don't have any experience with the mac consumer > API. (Whose job is it to do vlan tag insertion? The mac layers, or > the clients?) I suspect that someone needs to make up their mind about what the role of mhi_hdrsize is (set by calling mac_header_info()). Is it going to be the correct MAC header length (ie not 14 for _all_ ethernet packets) or is it going to be something else? That it isn't always correct seems to be avoided by the mac code that chooses not to call mac_header_info() for ethernet whilst it does for other protocols (feels like an optimisation to avoid all the other work in mac_header_info() on the "fast" ethernet path.) however dls_link_header_info() does it right: for VLAN packets, mhi_hdrsize is set to the size of the VLAN packet. I've filed 6862429 but.... Darren
