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

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Date:   Mon, 20 Apr 2020 15:21:23 -0300
From:   Paulo Alcantara <pc@....nz>
To:     David Howells <dhowells@...hat.com>
Cc:     dhowells@...hat.com, Steve French <smfrench@...il.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:

> Paulo Alcantara <pc@....nz> 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().
>
> Would that be a bug?

Probably.

I'm not sure how that code is supposed to work, TBH.