Re: [9fans] FreeBSD 9p work

[Alexander Viro <viro@math.psu.edu>]

On Thu, 12 Sep 2002, Geoff Collyer wrote:

> I say "NFS/vfs/vnode" because the edges of those things have always
> seemed blurry, but it's not essential to use NFS.  Is the vnode or VFS
> machinery really not sufficiently general to handle file system
> protocols other than NFS?

VFS is kernel mechanism - think of it as an equivalent of chan.c and
friends.  Filesystems provide methods; VFS calls them.  And that's
normal function calls.  It doesn't know anything about any protocols -
that stuff belongs to filesystem.

Notice that in Plan 9 _all_ userland filesystems are the same as far
as kernel is concerned - it's #m.  devmnt.c is just one of the kernel
filesystems and the fact that its implementation of methods happens
to talk 9P is its private business.  The rest of kernel doesn't know
or care about that.

To get 9P on FreeBSD you either need to provide a kernel filesystem
a-la devmnt.c or take existing kernel filesystem that would happen to
talk to userland and do protocol translation in userland.  In either
variant VFS will call (kernel) filesystem methods; then filesystem
will either talk 9P directly or talk some other protocol and have
userland process translate it into 9P.

The former requires writing a kernel fs.  The latter requires choosing
a protocol used by one of existing kernel filesystems and translating
between it and 9P.  AFAICS that will be messy for all such protocols -
none of them matches 9P well enough.