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Subject: Re: [PATCH] manpage: explain why showmount doesn't really work
 against a v4-only server
To:     "J. Bruce Fields" <bfields@fieldses.org>,
        Jeff Layton <jlayton@kernel.org>
Cc:     linux-nfs@vger.kernel.org, jfajerski@suse.com
References: <20190510215445.1823-1-jlayton@kernel.org>
 <20190511135442.GA15721@fieldses.org>
From:   Steve Dickson <SteveD@RedHat.com>
Message-ID: <fe3a9c31-a4cc-0a38-9a8f-1af53e7665d0@RedHat.com>
Date:   Wed, 29 May 2019 09:15:35 -0400
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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?

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;
>