svn commit: r275136 - in head/sys: dev/e1000 dev/ixgbe kern sys

[John Baldwin]

On Monday, December 01, 2014 07:19:13 AM Alfred Perlstein wrote:
> John,
> 
> Will work on a new revision based on feedback.
> 
> Two things to note however:
> 
> Already explored the idea of using kernel_sysctlbyname but rejected due to
> following:
> 
> It makes little sense to have a rw sysctl that only takes effect "some
> times". This violates POLA at the expense of making code appear cleaner.
> Expectation is that writable sysctls take effect or are read only. They are
> not to be "write sometimes" unless we are to introduce a new flag. Instead
> of going to a confusing model we consider some form of rw sysctl that can
> set itself ro somehow. Otherwise people will be confused as to why nic
> queues says N while actually M.  What the rw->ro api would look like I have
> no idea. Suggestions?

This is only somewhat true.  In the near distant future we will have a devctl 
tool which would let you do 'devctl detach igb0 && devctl attach igb0' which 
would honor your post-boot setting of hw.igb.num_queues.  Instead what is 
important to understand about this particular sysctl node is that it only 
takes affect when a device is attached.  However, there are other control 
knobs that also only affect future operations and not existing instances of 
objects, so I don't think this is that big of a leap.

-- 
John Baldwin