[openib-general] [PATCH] user_mad: Add receive side RMPP support

[Sean Hefty]

Fab Tillier wrote:
>>The user would need to know how large of a buffer to allocate for the read.
>>  If the user needs to allocate two buffers, then they either need to be
>>able to process data the spans multiple buffers, or a second data copy is
>>required.  There's also an issue if the user is using multiple threads...
> 
> 
> Ok, so my idea sucked.  What about not coalescing in the kernel, and just
> handing up MADs to be coalesced in user-mode?  It would require a buffer
> allocation in UM, as well as copies, but those currently happen in the kernel
> and could be eliminated, no?

Nah... your idea was fine as something to throw out.  :)

Currently, only a single data copy is performed to transfer received RMPP 
MADs from the kernel to a usermode app.  The coalescing occurs as the data 
is copied from a chain of MADs in the kernel to the app's buffer.

- Sean