Neil Brown wrote: > Hi. > > Suppose I have a mobile client such as a notebook computer which > changes networks from time to time - e.g. when "docked" it uses a > wired network, but when I "undock" it uses a wireless network. And > as I move around it might change from one wireless network to > another. > > Is it at all reasonable to expect that I could have an NFS mounted > filesystem that continues to work across all of those changes? > > If we just assume NFSv3 and ignore locking for the moment, then this > seems to work quite well if you use UDP, but fails badly if you use > TCP. This is because the connected socket holds on to the old source > address. Could this possibly be handled by some type of user-level connection manager that would be able to deal with the changing of a server's IP address? > > I think that the only way to get the client to close and re-open the > socket would be to wait for 5 minutes with no IO requests. But that > would be hard to ensure. Any attempt to access any file will trigger > a request which will keep retrying which will keep the socket active, > so the client won't close it.... It doesn't seem to work anyway. The > RPC client appears to try to connect from the same source IP address, > though I haven't checked the code to be sure of this. Again, this is where I think a connection manager could help... The kernel could do a "this server is broken give me another please" up-call and the CM could do all the needed host-to-address translation, making sure the IP address that is passed down a valid and working address... Continuing with this theory... this might be a cheap and dirty way of getting redundant or failover mount for v2/v3... with read-only mounts of course... > > Would it be worthwhile/practical to have a 'remount' mount option to > request that the socket be closed and re-opened? Only if we could teach autofs to do this... otherwise it should be auto-magically... imho.. > > If there were any active locks, there is probably nothing useful that > can be done for them. Unless the client manages to send a NOTIFY to > the server before changing IP address, the server will never drop the > locks. Maybe "-o remount,reopen" would only work if "-o nolocks" > were in force. It's not an ideal solution, but it might be better > than the current situations? Or read-only mounts... Meaning, we start with read-only and then move on to read/write mounts.. > > I'm not sure whether NFSv4 makes this easier or harder. Can you > continue a client session (SET_CLIENTID) from a different IP address? > Can you change the callback address for a CLIENT once it is created? I would think easier since there is less traffic between the server and client due to delegations... my two cents... steved. -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
