On May 31, 2012, at 11:40 AM, Jeff Layton wrote: > On Thu, 31 May 2012 10:28:49 -0400 > Chuck Lever <chuck.lever@xxxxxxxxxx> wrote: > >> >> On May 31, 2012, at 9:03 AM, Jeff Layton wrote: >> >>> If a NFS mount attempt fails with an ETIMEDOUT error, the mount.nfs code >>> doesn't currently attempt the next address in the list. For a NFSv4 mount >>> the initial mount() call almost always ends up going over >>> NFS_DEF_FG_TIMEOUT_MINUTES and the mount is never retried. >>> >>> For a v3 mount, it ends up continually retrying against the same IPv6 >>> address, and never tries the IPv4 address. Eventually it gives up once >>> it hits the NFS_DEF_FG_TIMEOUT_MINUTES timeout. >>> >>> It's possible that a server is just unreachable via IPv6 (due to a >>> routing misconfiguration for instance), or is dropping IPv6 frames on >>> the floor. In that situation, it might still be reachable via IPv4 and >>> trying the next address could have allowed the mount to succeed. >>> >>> Fix this by treating ETIMEDOUT in a similar fashion to ECONNREFUSED. >>> Have the client try the next address in the list before giving up and >>> returning an error. >> >> Bzzzzt. AF fallback is only legal to do if the admin did not specify a netid. >> >> Can you demonstrate that your patch works correctly if an IPv6 netid is specified? "Correctly" here means that no fallback occurs. >> > > If someone specifies an IPv6 netid (via proto= option) then we would > set AF_INET6 in the addrinfo "hints" and there will be no IPv4 > addresses in the mi->address list. So, this does still work correctly > when someone specifies an ipv6 netid. > > Chuck also pointed out on IRC that the description was a little > unclear, since it was specific to my test rig where the server had a > single IPv6 and IPv4 address in DNS. > > The loop that retries against different addresses doesn't care > about whether the addrs are v4 or v6. Correct. Moreover, we do get the right behavior because the initial DNS lookup populates the list of addresses to try, based on a specified netid (proto=). Thus, if no netid is specified, the list contains INET and INET6; if a netid is specified, the list contains only one address family. That properly limits the addresses that can be used when mount.nfs retries. > What this really tells mount.nfs > to do is to keep trying different addresses in the list if there are > any instead of giving up on an ETIMEDOUT error. > > -- > Jeff Layton <jlayton@xxxxxxxxxx> > -- > 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 -- Chuck Lever chuck[dot]lever[at]oracle[dot]com -- 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
