one thing of note, linux vfs implements a dcache. this connects the
virtual memory system to the filesystem. (but oddly in linux network
buffers are handled seperately.) there is no client-side caching in
the plan 9 kernel.
there is a notable exception. there is an executable cache.
>> One more point, I googled a lot on "kernel resident file systems and
>> non kernel resident file systems", but I could not find a single
>> useful link. It would be great if you could specify the difference
>> between the two. I wish that eases up the situation a bit.
since the devtab[] functions map 1:1 with 9p, all the mount driver
needs to do for calls outside the kernel is to marshal/demarshal
9p messages.
it's important to remember that most in-kernel file servers could easily
exist outside the kernel. the entire ip stack can be implemented from
user space. (and it has been in the past.)
> "Kernel resident filesystem" in this context simply means a filesystem
> which was created for use by the kernel; this may or may not be
> visible to user-space applications - I'm not too sure.
every element of mounttab[] has an associated device letter. to
mount the device, one does (typically)
bind -a '#'^$letter /dev
for example, to bind a second ip stack on /net.alt,
bind -a '#I1' /net.alt
> To sum up, you
> use the 9 primitive operations provided by each 'Dev' when you work
> with kernel-resident filesystems, while all other filesystems are
> dealt with using regular 9P.
all devices are accessed through devtab. it may be that that entry
is the mount driver. the mount driver turns devtab[]->fn into
the corresponding 9p message. (and vice versa.)
- erik
