mount.nfs4 clientaddr= option inconsistent behaviour

Hi,

There is an inconsistent behaviour of mount.nfs4 regarding how to detect/handle the client IP address.
The "clientaddr" option is allowed for mount.nfs4, but this address is not used for the client IP address, and if there is any DNS failure or misconfiguration, mount.nfs4 will fail.

The error is in get_my_ipv4addr() at nfs4mount.c:170 (nfs-utils-1.1.0). This function fills *ip_addr with the client address, detected from the resolved machine name (gethostname() which is tried to be resolved in fill_ipv4_sockaddr). This cannot work if the machine name is not (yet) properly resolvable in DNS at mount time (e.g. we are nfs4-mounting the root filesystem very early). Using the clientaddr option provided before trying to resolve the gethostname() hostname, would be IMHO a more consistent behaviour.

This can cause much trouble too with multihomed clients. The right way would be to detect the client IP from the server IP (or resolved IP) (and deal with clients with multiple addresses per subnet, by taking the lowest address only)

Patch for this is easy (the first part, not the ip detection code), and can be provided if necessary.

Gabriel

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Hi Gabriel-

I may be mistaken, but I don't think that the Linux NFSv4 implementation is made for mounting the root file system. You may be wandering into an area that has had no testing, and in fact, the implementation may not be designed to do this at all.

Yes, this is good analysis, I think. Neil Brown added some logic to mount recently that determines the client's IP address by opening a socket to the server, and capturing the local endpoint's address. This takes into account which network interface is used on the client to contact the server. I'm not sure whether this logic is used for determining the clientaddr address yet.

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