Re: [RFC] Netlink and user-space buffer pointers

[Mike Christie <michaelc@cs.wisc.edu>]

snipped lkml and netdev. I do not think they care do they.

James Smart wrote:
> Note: We've transitioned off topic. If what this means is "there isn't a
> good
> way except by ioctls (which still isn't easily portable) or system calls",
> then that's ok. Then at least we know the limits and can look at other
> implementation alternatives.
> 

So we have

1. sysfs: prbably bad becuase to pass down every attr for the command we
need a seperate file. This does not seem like it meets the binary sysfs
file requirement.

2. configfs: again bad becuase we have to pass down eveyr attr for the
command in a speperate file.

3. ioctl: Christoph has not allowed scsi drivers to add ioctls so I
doubt he would let some other scsi code let it.

4. syscall:

5. netlink: netdev guys do not want use to pass pointers. So we either
have a worst case double copy (copy from userspace to network and
network to buffer that is within the LLDs queue limits (do like sg where
it as a preallocated buffer)) or if we used the bio code like how the
ll_rw_blk.c does just fail if the command is to large. In some cases the
io may just be too large and have to fail though.

	5A. modify netlink to copy data to a buffer that is within some sort of
limits we can DMA from.
	5B. debate with netdev guys about passing poitners, in which case we
could have some of the problem 5 has in that when we map data we do not
have much control over the pages so we may have to drop down to a copy
to some preallocate buffer or fail model.

6. char device

7. what else...