Linux kernel compatability

Nathan Whitehorn nwhitehorn at freebsd.org
Tue Jan 4 16:05:34 UTC 2011


On 01/04/11 07:22, Alexander Kabaev wrote:
> On Mon, 3 Jan 2011 19:03:01 -1000 (HST)
> Jeff Roberson<jroberson at jroberson.net>  wrote:
>
>> On Mon, 3 Jan 2011, Alexander Kabaev wrote:
>>
>>> On Mon, 3 Jan 2011 10:31:24 -1000 (HST)
>>> Jeff Roberson<jroberson at jroberson.net>  wrote:
>> I would argue that the layer works very well for infiniband.  Much
>> better than almost.  It is only almost complete in that there is no
>> need for me to implement features that we're not using.
>>
>> I am interested in hearing your other concerns however.
>>
>> Thanks,
>> Jeff
>>
>
> The considerations are simple enough. First, we do not have many IB
> users of FreeBSD in the wild and those that we have (Isilon) seem to be
> perfectly capable of managing the IB stack out of the tree, without
> dumping the thousands of lines of the code into the base. If they had
> the stack before, but were not willing/capable to provide adequate care
> for it in the past, there is no reason to expect things to change with
> second stack, which now will rot in our tree instead of theirs.

Before this, it was very difficult to be an Infiniband user on FreeBSD, 
which I think explains the dearth. And that Isilon chose to port this 
giant piece of code twice indicates that they do care very much.

> Second, semi-complete Linux compat layer in kernel will have the
> same effect as linuxulator in userland - we do have some vendors still
> trying to bother with FreeBSD drivers for their hardware now and we
> will have none after we provide the possibility to hack their Linux
> code to run somewhat stably on top of Linux compat layer. Due to
> intentional fluidity of Linux kAPI, our shims will never quite walk and
> quack like their original implementation in Linux kernel and combined
> result will always be lees stable than native Linux linux drivers in
> Linux kernel.

This is perhaps an argument for keeping it tightly coupled to the 
Infiniband stack, but certainly not for keeping it out of the tree. It 
seems that most vendor drivers have their own adaptation layer anyway 
and it would be just as easy for them to continue supporting FreeBSD as 
they always have. Project Evil did not lead to a huge decrease in 
availability of FreeBSD network drivers. As far as I understand, as 
well, this emulation layer is much less complete even than our NDIS support.
-Nathan


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