On 9 February 2016 at 12:19, David Gwynne <[email protected]> wrote: > >> On 9 Feb 2016, at 9:12 PM, Mike Belopuhov <[email protected]> wrote: >> >> On 9 February 2016 at 11:31, David Gwynne <[email protected]> wrote: >>> On Mon, Feb 08, 2016 at 11:02:06PM +1000, David Gwynne wrote: >>>> On Sat, Feb 06, 2016 at 04:43:28PM -0500, Anthony Eden wrote: >>>>>> Synopsis: <alignment fault on armv7 (omap) using carp(4)> >>>>> >>>>> To me that behavior might suggest the problem is deeper than a >>>>> bookkeeping mistake of aligning memory in mbuf. >>>> >>>> nope, you were right, it's a screwup with alignment. >>>> >>>> the problem is multicast packets that arent to a carp interfaces >>>> mac address have to be duplicated and sent to all carp interfaces >>>> on a parent. the duplication is done with m_copym2, which doesn't >>>> respect the alignment requirements of the ip header inside the 14 >>>> byte ethernet header. >>>> >>>> the following dups the packet inside carp, and makes sure the >>>> ethernet payload is aligned properly. >>>> >>>> i was able to reproduce this on sparc64, and i believe this fixes >>>> it. could you test it and see if it helps? >>> >>> mpi@ pointed out that bridge@ has a special function to do a deep >>> copy of mbufs that get the ip payload alignment right, and that we >>> should share. >>> >>> this moves the functionality in with the rest of the mbuf functions. >>> >>> could a bridge user test this to see if it still works? carp seems >>> fine with this on sparc64 stil. >>> >>> ok? >>> >> >> m_adj can be done as part of the m_copym2 as well. > > you want to shove m_adj into m_copym2? or you want m_copym2 callers to > m_prepend 2 bytes first? > >> In the long run I don't think that introducing a new function >> makes sense, not sure about 5.9 and right now, though. > > im not sure using m_copym2 for a deep copy makes that much sense generally. > it's not a great implementation, and the vast majority of the callers use it > to copy everything.
after talking to dlg@ i think that I'd prefer something like m_copypacket from FreeBSD that preserves the alignment of the first mbuf in the chain.
