4.13 32 bit clients/servers and 64 bit clients/servers

The 64 bit nature of the NFS version 3 protocol introduces several compatibility problems. The most notable two are mismatched clients and servers, that is, a 32 bit client and a 64 bit server or a 64 bit client and a 32 bit server.

The problems of a 64 bit client and a 32 bit server are easy to handle. The client will never encounter a file that it can not handle. If it sends a request to the server that the server can not handle, the server should reject the request with an appropriate error.

The problems of a 32 bit client and a 64 bit server are much harder to handle. In this situation, the server does not have a problem because it can handle anything that the client can generate. However, the client may encounter a file that it can not handle. The client will not be able to handle a file whose size can not be expressed in 32 bits. Thus, the client will not be able to properly decode the size of the file into its local attributes structure. Also, a file can grow beyond the limit of the client while the client is accessing the file.

The solutions to these problems are left up to the individual implementor. However, there are two common approaches used to resolve this situation. The implementor can choose between them or even can invent a new solution altogether. The most common solution is for the client to deny access to any file whose size can not be expressed in 32 bits. This is probably the safest, but does introduce some strange semantics when the file grows beyond the limit of the client while it is being access by that client. The file becomes inaccessible even while it is being accessed.

The second solution is for the client to map any size greater than it can handle to the maximum size that it can handle. Effectively, it is lying to the application program. This allows the application access as much of the file as possible given the 32 bit offset restriction. This eliminates the strange semantic of the file effectively disappearing after it has been accessed, but does introduce other problems. The client will not be able to access the entire file.

Currently, the first solution is the recommended solution. However, client implementors are encouraged to do the best that they can to reduce the effects of this situation.