[linux-cifs-client] DFS support in CIFS

[Steve French]

> Currently I'm writing DFS support in cifs kernel module
> At current state I can work read/write/list files in DFS shares and so on.
> Only two big things hasn't been done:

2. not enough knowledge to do propper cleanup when cleaning nested 
trees, module crashes on 'rmmod cifs'

So, Does anybody know a way to accomplish 1 problem or any proposal how 


I had finished part of the code necessary for DFS a few years ago (and 
they are in mainline) as you have probably noticed.

CIFS code can recognize DFS referral, get the referral list - and for 
referrals with server as ip address could probably work today with small 
changes.  ip address based referrals are ok, although not common.


> 1. resolving server names to ip in kernel space
I think the easiest approach for kernels 2.6.12 or later will be to define a key type (keyed on hostname) for the upcall and use the
key management api to return the ip address (see Documentation/keys.txt etc and Dave Howells web page at RedHat).  Most other
upcall possibilities (captive ioctl, cn.ko, or worse netlink, or pseudo-fs require a long running daemon which is 
probably not ideal, and also have some problems with reliability).  This should probably not be a cifs specific key type
but cifs would be the first user of it.


>2. not enough knowledge to do propper cleanup when cleaning nested 
> trees, module crashes on 'rmmod cifs'
There may be a way to do this with explicit mounts from a daemon in userspace (I hope we can avoid this) but surely this
is something the automounter deals with.  Again the key request api (with a null, noncached key - passing as description
the mount parms you want to issue?) might work.  An alternative if mount in kernel could be to attached a list of the
"sub-mounts" (implicit dfs mounts) off the CIFS_SB (cifs specific portion of the superblock).

In any case - let's discuss this more.  I would like to take a look at integrating this - the DFS code has languished too long.