netdev - Re: What's a good default TTL for DNS keys in the kernel

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Message-ID: <87imhvj7m6.fsf@cjr.nz>
Date:   Sun, 19 Apr 2020 21:58:25 -0300
From:   Paulo Alcantara <pc@....nz>
To:     David Howells <dhowells@...hat.com>,
        Steve French <smfrench@...il.com>
Cc:     dhowells@...hat.com, linux-nfs <linux-nfs@...r.kernel.org>,
        CIFS <linux-cifs@...r.kernel.org>, linux-afs@...ts.infradead.org,
        ceph-devel@...r.kernel.org, keyrings@...r.kernel.org,
        Network Development <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>, fweimer@...hat.com
Subject: Re: What's a good default TTL for DNS keys in the kernel

David Howells <dhowells@...hat.com> writes:

> Steve French <smfrench@...il.com> wrote:
>
>> For SMB3/CIFS mounts, Paulo added support last year for automatic
>> reconnect if the IP address of the server changes.  It also is helpful
>> when DFS (global name space) addresses change.
>
> What happens if the IP address the superblock is going to changes, then
> another mount is made back to the original IP address?  Does the second mount
> just pick the original superblock?

It is going to transparently reconnect to the new ip address, SMB share,
and cifs superblock is kept unchanged.  We, however, update internal
TCP_Server_Info structure to reflect new destination ip address.

For the second mount, since the hostname (extracted out of the UNC path
at mount time) resolves to a new ip address and that address was saved earlier
in TCP_Server_Info structure during reconnect, we will end up
reusing same cifs superblock as per fs/cifs/connect.c:cifs_match_super().