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Date:   Wed, 29 May 2019 09:24:41 -0400
From:   "J. Bruce Fields" <bfields@fieldses.org>
To:     Steve Dickson <SteveD@RedHat.com>
Cc:     Jeff Layton <jlayton@kernel.org>, linux-nfs@vger.kernel.org,
        jfajerski@suse.com
Subject: Re: [PATCH] manpage: explain why showmount doesn't really work
 against a v4-only server
Message-ID: <20190529132441.GA8235@fieldses.org>
References: <20190510215445.1823-1-jlayton@kernel.org>
 <20190511135442.GA15721@fieldses.org>
 <fe3a9c31-a4cc-0a38-9a8f-1af53e7665d0@RedHat.com>
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On Wed, May 29, 2019 at 09:15:35AM -0400, Steve Dickson wrote:
> Bruce,
> 
> On 5/11/19 9:54 AM, J. Bruce Fields wrote:
> > On Fri, May 10, 2019 at 05:54:45PM -0400, Jeff Layton wrote:
> >> From: Jeff Layton <jlayton@redhat.com>
> >>
> >> I occasionally see people that expect valid info when running showmount
> >> against a server that may export some or all filesystems via NFSv4.
> >> Let's make it clear that it only works by talking to the remote MNT
> >> service, and that that may not be available from a v4-only server.
> > 
> > Looks fine.
> > 
> > I wonder if it'd also be helpful for showmount to detect this case and
> > say something.  E.g. the following (not even compileable, but you get
> > the idea).
> > 
> > We've also talked about trying to cobble together an export list by
> > scanning the root filesystem over NFSv4, but that's likely to be
> > complicated and wouldn't give all the same results without further
> > protocol extensions anyway, so I think that idea's dead.
> > 
> > --b.
> I'm a bit confused... Does this patch go along with Jeff's manpage change?

It's separate.  And doesn't even compile.  You can ignore it for now.

--b.

> 
> steved.
> > 
> > diff --git a/utils/showmount/showmount.c b/utils/showmount/showmount.c
> > index 394f5284a219..de9a6d38783a 100644
> > --- a/utils/showmount/showmount.c
> > +++ b/utils/showmount/showmount.c
> > @@ -115,6 +115,22 @@ static CLIENT *nfs_get_mount_client(const char *hostname, rpcvers_t vers)
> >  	exit(1);
> >  }
> >  
> > +void warn_if_v4_only(char *hostname)
> > +{
> > +	struct sockaddr_in server_addr, client_addr;
> > +
> > +	if (fill_ipv4_sockaddr(hostname, &serveraddr))
> > +		return;
> > +	server_addr.sin_port = htnos(NFS_PORT);
> > +	client_addr.sin_family = 0;
> > +	client_addr.sin_addr.s_addr = 0;
> > +	clnt_ping(&server_addr, NFS_PROGRAM, 4, "tcp", &client_addr);
> > +
> > +	if (rpc.createerr == RPC_SUCCESS)
> > +		printf("Server responding to NFSv4 but not MNT; try mounting "
> > +			"%s:/ instead of showmount", hostname);
> > +}
> > +
> >  int main(int argc, char **argv)
> >  {
> >  	char hostname_buf[MAXHOSTLEN];
> > @@ -199,6 +215,7 @@ int main(int argc, char **argv)
> >  		fprintf(stderr, "%s: unable to create RPC auth handle.\n",
> >  				program_name);
> >  		clnt_destroy(mclient);
> > +		warn_if_v4_only(hostname);
> >  		exit(1);
> >  	}
> >  	total_timeout.tv_sec = TOTAL_TIMEOUT;
> >