First off, I really am a big fan of filesystem interfaces as used in Plan
9 - after all my PhD work was based on the model :)
My objective here is to debate and understand how the points made in the
paper relate to the Plan9 networking model.
* performance overhead: app requesting data from a socket typically
needs to perform 2 system calls (select/read or alt/read)
alt ? which is not required ? is not a system call. only a read or write is
required.
Well, select() or alt might or might not be required depending on whether
you want your thread to wait till the read operation waiting
for data from the network completes. You may argue that since threads are
"cheap" in Plan9 you can afford to have a thread wait on the read
operation. But that to me is a different question...
* lack of an "kernel up-call API": which allows the kernel to inform an
app each time network data is available
plan 9 uses synchronous i/o, so this statement doesn't make sense
in plan 9. you can use threads to do i/o asynch w.r.t. your application,
but the i/o itself is still synchronous w.r.t. the kernel.
Whether the IO is synchronous or not, there is this
read()->process()->read()... alternating sequence of operations that is
required, wherein the application has to explicitly go fetch data from the network
using the read operation. To borrow text from the paper:
<snip>
The API does not provide the programmer a way in which to say, "Whenever
there is data for me, call me to process it directly."
</snip>
* hard to implement "multi homing" with support for multiple network
interfaces
i have no idea how this relates to the use of a fs in implementing the
network stack. why would using a filsystem (or not) make any difference
in the ability to multihome?
by the way, plan 9 beats the pants off anything else i've used for multiple
network / interface support. it's support for mulitple ip stacks is quite
neat.
The question was meant to ask as to how easy it is to programmatically
use the filesystem interface in a multi home network. But I agree that support for
multiple network interfaces in Plan9 is way superior.
