[PATCH] showmount: try v3 before falling back to v1

[PATCH] showmount: try v3 before falling back to v1

[Dan McGee]

A lot of people don't have anything below v3 enabled, so showmount is
completely unusable. Try v3 {tcp, udp} first; if they don't work, fall back
to v1 {tcp, udp}; if those don't work then just fail as before.

Signed-off-by: Dan McGee <dpmcgee@gmail.com>
---

First (and quick) attempt at a patch here for showmount. Let me know if you see
serious problems with it or the approach. It seemed relatively sane to me and
fixed my problems after brief testing.

See a report like this for some proof this is an issue in the wild:
http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=557954

Thanks,

-Dan

 utils/showmount/showmount.c |    8 ++++++++
 1 files changed, 8 insertions(+), 0 deletions(-)

diff --git a/utils/showmount/showmount.c b/utils/showmount/showmount.c
index 418e8b9..716c06d 100644
--- a/utils/showmount/showmount.c
+++ b/utils/showmount/showmount.c
@@ -96,6 +96,14 @@ static CLIENT *nfs_get_mount_client(const char *hostname)
 	rpcprog_t program = nfs_getrpcbyname(MOUNTPROG, nfs_sm_pgmtbl);
 	CLIENT *client;
 
+	client = clnt_create(hostname, program, MOUNTVERS_NFSV3, "tcp");
+	if (client)
+		return client;
+
+	client = clnt_create(hostname, program, MOUNTVERS_NFSV3, "udp");
+	if (client)
+		return client;
+
 	client = clnt_create(hostname, program, MOUNTVERS, "tcp");
 	if (client)
 		return client;
-- 
1.6.6

Re: [PATCH] showmount: try v3 before falling back to v1

[Chuck Lever]

On Jan 4, 2010, at 8:34 PM, Dan McGee wrote:

> A lot of people don't have anything below v3 enabled, so showmount is
> completely unusable. Try v3 {tcp, udp} first; if they don't work,  
> fall back
> to v1 {tcp, udp}; if those don't work then just fail as before.

I don't see any immediate problems with this.

It might be nice to add a command line option to select which  
transport to use, but that's entirely optional.

> Signed-off-by: Dan McGee <dpmcgee@gmail.com>
> ---
>
> First (and quick) attempt at a patch here for showmount. Let me know  
> if you see
> serious problems with it or the approach. It seemed relatively sane  
> to me and
> fixed my problems after brief testing.
>
> See a report like this for some proof this is an issue in the wild:
> http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=557954
>
> Thanks,
>
> -Dan
>
> utils/showmount/showmount.c |    8 ++++++++
> 1 files changed, 8 insertions(+), 0 deletions(-)
>
> diff --git a/utils/showmount/showmount.c b/utils/showmount/showmount.c
> index 418e8b9..716c06d 100644
> --- a/utils/showmount/showmount.c
> +++ b/utils/showmount/showmount.c
> @@ -96,6 +96,14 @@ static CLIENT *nfs_get_mount_client(const char  
> *hostname)
> 	rpcprog_t program = nfs_getrpcbyname(MOUNTPROG, nfs_sm_pgmtbl);
> 	CLIENT *client;
>
> +	client = clnt_create(hostname, program, MOUNTVERS_NFSV3, "tcp");
> +	if (client)
> +		return client;
> +
> +	client = clnt_create(hostname, program, MOUNTVERS_NFSV3, "udp");
> +	if (client)
> +		return client;
> +
> 	client = clnt_create(hostname, program, MOUNTVERS, "tcp");
> 	if (client)
> 		return client;
> -- 
> 1.6.6
>
> --
> To unsubscribe from this list: send the line "unsubscribe linux-nfs"  
> in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html

-- 
Chuck Lever
chuck[dot]lever[at]oracle[dot]com

Re: [PATCH] showmount: try v3 before falling back to v1

[Steve Dickson]

On 01/05/2010 12:31 PM, Chuck Lever wrote:
> 
> On Jan 4, 2010, at 8:34 PM, Dan McGee wrote:
> 
>> A lot of people don't have anything below v3 enabled, so showmount is
>> completely unusable. Try v3 {tcp, udp} first; if they don't work, fall
>> back
>> to v1 {tcp, udp}; if those don't work then just fail as before.
> 
> I don't see any immediate problems with this.
> 
Well I do have a bz request that we stop using the lower mount
version so we can move away from NFSv2 support... so here is
my version of this patch... 

Comments??

steved.


Author: Steve Dickson <steved@redhat.com>
Date:   Tue Jan 5 13:29:07 2010 -0500

    showmount: Try the highest mount version then fall back to lower ones
    
    Showmount should try the highest mount version first then fall
    back to the lower ones when the server returns a RPC_PROGVERSMISMATCH
    error. The idea being not using the lower mount versions will begin
    the process of moving away from NFSv2 support.
    
    Signed-off-by: Steve Dickson <steved@redhat.com>

diff --git a/utils/showmount/showmount.c b/utils/showmount/showmount.c
index 418e8b9..17224a6 100644
--- a/utils/showmount/showmount.c
+++ b/utils/showmount/showmount.c
@@ -85,22 +85,29 @@ static const char *nfs_sm_pgmtbl[] = {
 	NULL,
 };
 
+static const int mount_vers[] = {
+	MOUNTVERS_NFSV3,
+	MOUNTVERS_POSIX,
+	MOUNTVERS,
+};
+static const int max_vers = (sizeof(mount_vers)/sizeof(mount_vers[0]));
+
 /*
  * Generate an RPC client handle connected to the mountd service
  * at @hostname, or die trying.
  *
  * Supports both AF_INET and AF_INET6 server addresses.
  */
-static CLIENT *nfs_get_mount_client(const char *hostname)
+static CLIENT *nfs_get_mount_client(const char *hostname, int vers)
 {
 	rpcprog_t program = nfs_getrpcbyname(MOUNTPROG, nfs_sm_pgmtbl);
 	CLIENT *client;
 
-	client = clnt_create(hostname, program, MOUNTVERS, "tcp");
+	client = clnt_create(hostname, program, vers, "tcp");
 	if (client)
 		return client;
 
-	client = clnt_create(hostname, program, MOUNTVERS, "udp");
+	client = clnt_create(hostname, program, vers, "udp");
 	if (client)
 		return client;
 
@@ -122,7 +129,7 @@ int main(int argc, char **argv)
 	mountlist list;
 	int i;
 	int n;
-	int maxlen;
+	int maxlen, vers=0;
 	char **dumpv;
 
 	program_name = argv[0];
@@ -185,7 +192,8 @@ int main(int argc, char **argv)
 		break;
 	}
 
-	mclient = nfs_get_mount_client(hostname);
+again:
+	mclient = nfs_get_mount_client(hostname, mount_vers[vers]);
 	mclient->cl_auth = authunix_create_default();
 	total_timeout.tv_sec = TOTAL_TIMEOUT;
 	total_timeout.tv_usec = 0;
@@ -197,6 +205,10 @@ int main(int argc, char **argv)
 			(xdrproc_t) xdr_void, NULL,
 			(xdrproc_t) xdr_exports, (caddr_t) &exportlist,
 			total_timeout);
+		if (clnt_stat == RPC_PROGVERSMISMATCH) {
+			if (++vers <  max_vers)
+				goto again;
+		}
 		if (clnt_stat != RPC_SUCCESS) {
 			clnt_perror(mclient, "rpc mount export");
 			clnt_destroy(mclient);
@@ -232,6 +244,10 @@ int main(int argc, char **argv)
 		(xdrproc_t) xdr_void, NULL,
 		(xdrproc_t) xdr_mountlist, (caddr_t) &dumplist,
 		total_timeout);
+	if (clnt_stat == RPC_PROGVERSMISMATCH) {
+		if (++vers <  max_vers)
+			goto again;
+	}
 	if (clnt_stat != RPC_SUCCESS) {
 		clnt_perror(mclient, "rpc mount dump");
 		clnt_destroy(mclient);

Re: [PATCH] showmount: try v3 before falling back to v1

[Chuck Lever]

On Jan 5, 2010, at 1:38 PM, Steve Dickson wrote:

> On 01/05/2010 12:31 PM, Chuck Lever wrote:
>>
>> On Jan 4, 2010, at 8:34 PM, Dan McGee wrote:
>>
>>> A lot of people don't have anything below v3 enabled, so showmount  
>>> is
>>> completely unusable. Try v3 {tcp, udp} first; if they don't work,  
>>> fall
>>> back
>>> to v1 {tcp, udp}; if those don't work then just fail as before.
>>
>> I don't see any immediate problems with this.
>>
> Well I do have a bz request that we stop using the lower mount
> version so we can move away from NFSv2 support... so here is
> my version of this patch...
>
> Comments??
>
> steved.
>
>
> Author: Steve Dickson <steved@redhat.com>
> Date:   Tue Jan 5 13:29:07 2010 -0500
>
>    showmount: Try the highest mount version then fall back to lower  
> ones
>
>    Showmount should try the highest mount version first then fall
>    back to the lower ones when the server returns a  
> RPC_PROGVERSMISMATCH
>    error. The idea being not using the lower mount versions will begin
>    the process of moving away from NFSv2 support.
>
>    Signed-off-by: Steve Dickson <steved@redhat.com>
>
> diff --git a/utils/showmount/showmount.c b/utils/showmount/showmount.c
> index 418e8b9..17224a6 100644
> --- a/utils/showmount/showmount.c
> +++ b/utils/showmount/showmount.c
> @@ -85,22 +85,29 @@ static const char *nfs_sm_pgmtbl[] = {
> 	NULL,
> };
>
> +static const int mount_vers[] = {

RPC version numbers are rpcvers_t, not int.

The array above this one is called "nfs_sm_pgmtbl"... to be consistent  
with existing code you should name this one "nfs_sm_verstbl".

> +	MOUNTVERS_NFSV3,
> +	MOUNTVERS_POSIX,
> +	MOUNTVERS,
> +};
> +static const int max_vers = (sizeof(mount_vers)/ 
> sizeof(mount_vers[0]));

Array indices are unsigned.

Calling this "max_vers" suggests it's actually a version number, and  
not an index into the version array; that's confusing.

The array above this one has a NULL entry as it's final element.  To  
be consistent with existing code, you should copy that logic for this  
array instead of using a separate "max_vers" variable.

> +
> /*
>  * Generate an RPC client handle connected to the mountd service
>  * at @hostname, or die trying.
>  *
>  * Supports both AF_INET and AF_INET6 server addresses.
>  */
> -static CLIENT *nfs_get_mount_client(const char *hostname)
> +static CLIENT *nfs_get_mount_client(const char *hostname, int vers)

RPC version numbers are rpcvers_t, not int.  At the very least,  
clnt_create(3t) takes an unsigned version number argument.

> {
> 	rpcprog_t program = nfs_getrpcbyname(MOUNTPROG, nfs_sm_pgmtbl);
> 	CLIENT *client;
>
> -	client = clnt_create(hostname, program, MOUNTVERS, "tcp");
> +	client = clnt_create(hostname, program, vers, "tcp");
> 	if (client)
> 		return client;
>
> -	client = clnt_create(hostname, program, MOUNTVERS, "udp");
> +	client = clnt_create(hostname, program, vers, "udp");
> 	if (client)
> 		return client;
>
> @@ -122,7 +129,7 @@ int main(int argc, char **argv)
> 	mountlist list;
> 	int i;
> 	int n;
> -	int maxlen;
> +	int maxlen, vers=0;

Array indices are unsigned integers.

Calling this "vers" suggests it's actually a version number, and not  
an index into the version array; that's confusing.

> 	char **dumpv;
>
> 	program_name = argv[0];
> @@ -185,7 +192,8 @@ int main(int argc, char **argv)
> 		break;
> 	}
>
> -	mclient = nfs_get_mount_client(hostname);
> +again:
> +	mclient = nfs_get_mount_client(hostname, mount_vers[vers]);
> 	mclient->cl_auth = authunix_create_default();
> 	total_timeout.tv_sec = TOTAL_TIMEOUT;
> 	total_timeout.tv_usec = 0;
> @@ -197,6 +205,10 @@ int main(int argc, char **argv)
> 			(xdrproc_t) xdr_void, NULL,
> 			(xdrproc_t) xdr_exports, (caddr_t) &exportlist,
> 			total_timeout);
> +		if (clnt_stat == RPC_PROGVERSMISMATCH) {
> +			if (++vers <  max_vers)
> +				goto again;
> +		}

clnt_create(3t) should tell you if the requested version number is  
working; libtirpc's version does a NULLPROC call, for example.  It  
would be simpler to move this check into nfs_get_mount_client(), then  
you wouldn't need the retry loop here.

But nfs_get_mount_client() already doesn't care why the  
clnt_create(3t) call fails, it just retries the creation with  
different parameters if it didn't succeed.  Do we really care enough  
to retry _only_ if the specific RPC version isn't available?  We use  
the same procedure number with the same arguments and the same results  
for all three protocol versions, yes?

> 		if (clnt_stat != RPC_SUCCESS) {
> 			clnt_perror(mclient, "rpc mount export");
> 			clnt_destroy(mclient);
> @@ -232,6 +244,10 @@ int main(int argc, char **argv)
> 		(xdrproc_t) xdr_void, NULL,
> 		(xdrproc_t) xdr_mountlist, (caddr_t) &dumplist,
> 		total_timeout);
> +	if (clnt_stat == RPC_PROGVERSMISMATCH) {
> +		if (++vers <  max_vers)
> +			goto again;
> +	}
> 	if (clnt_stat != RPC_SUCCESS) {
> 		clnt_perror(mclient, "rpc mount dump");
> 		clnt_destroy(mclient);

-- 
Chuck Lever
chuck[dot]lever[at]oracle[dot]com

Re: [PATCH] showmount: try v3 before falling back to v1

[Steve Dickson]

On 01/05/2010 02:23 PM, Chuck Lever wrote:
>>
>> Author: Steve Dickson <steved@redhat.com>
>> Date:   Tue Jan 5 13:29:07 2010 -0500
>>
>>    showmount: Try the highest mount version then fall back to lower ones
>>
>>    Showmount should try the highest mount version first then fall
>>    back to the lower ones when the server returns a RPC_PROGVERSMISMATCH
>>    error. The idea being not using the lower mount versions will begin
>>    the process of moving away from NFSv2 support.
>>
>>    Signed-off-by: Steve Dickson <steved@redhat.com>
>>
>> diff --git a/utils/showmount/showmount.c b/utils/showmount/showmount.c
>> index 418e8b9..17224a6 100644
>> --- a/utils/showmount/showmount.c
>> +++ b/utils/showmount/showmount.c
>> @@ -85,22 +85,29 @@ static const char *nfs_sm_pgmtbl[] = {
>>     NULL,
>> };
>>
>> +static const int mount_vers[] = {
> 
> RPC version numbers are rpcvers_t, not int.
True..

> 
> The array above this one is called "nfs_sm_pgmtbl"... to be consistent
> with existing code you should name this one "nfs_sm_verstbl".
> 
>> +    MOUNTVERS_NFSV3,
>> +    MOUNTVERS_POSIX,
>> +    MOUNTVERS,
>> +};
>> +static const int max_vers = (sizeof(mount_vers)/sizeof(mount_vers[0]));
> 
> Array indices are unsigned.
Sure... 

> 
> Calling this "max_vers" suggests it's actually a version number, and not
> an index into the version array; that's confusing.
Its pretty simple code.. don't see this confusion.... but..
It changed to  mount_vers_tbl
> 
> The array above this one has a NULL entry as it's final element.  To be
> consistent with existing code, you should copy that logic for this array
> instead of using a separate "max_vers" variable.
Having the NULL messes up the sizeof calculations
 
> 
>> +
>> /*
>>  * Generate an RPC client handle connected to the mountd service
>>  * at @hostname, or die trying.
>>  *
>>  * Supports both AF_INET and AF_INET6 server addresses.
>>  */
>> -static CLIENT *nfs_get_mount_client(const char *hostname)
>> +static CLIENT *nfs_get_mount_client(const char *hostname, int vers)
> 
> RPC version numbers are rpcvers_t, not int.  At the very least,
> clnt_create(3t) takes an unsigned version number argument.
> 
>> {
>>     rpcprog_t program = nfs_getrpcbyname(MOUNTPROG, nfs_sm_pgmtbl);
>>     CLIENT *client;
>>
>> -    client = clnt_create(hostname, program, MOUNTVERS, "tcp");
>> +    client = clnt_create(hostname, program, vers, "tcp");
>>     if (client)
>>         return client;
>>
>> -    client = clnt_create(hostname, program, MOUNTVERS, "udp");
>> +    client = clnt_create(hostname, program, vers, "udp");
>>     if (client)
>>         return client;
>>
>> @@ -122,7 +129,7 @@ int main(int argc, char **argv)
>>     mountlist list;
>>     int i;
>>     int n;
>> -    int maxlen;
>> +    int maxlen, vers=0;
> 
> Array indices are unsigned integers.
> 
> Calling this "vers" suggests it's actually a version number, and not an
> index into the version array; that's confusing.
and an index call 'j' or 'i' is descriptive?? vers is clear enough imho...

> 
>>     char **dumpv;
>>
>>     program_name = argv[0];
>> @@ -185,7 +192,8 @@ int main(int argc, char **argv)
>>         break;
>>     }
>>
>> -    mclient = nfs_get_mount_client(hostname);
>> +again:
>> +    mclient = nfs_get_mount_client(hostname, mount_vers[vers]);
>>     mclient->cl_auth = authunix_create_default();
>>     total_timeout.tv_sec = TOTAL_TIMEOUT;
>>     total_timeout.tv_usec = 0;
>> @@ -197,6 +205,10 @@ int main(int argc, char **argv)
>>             (xdrproc_t) xdr_void, NULL,
>>             (xdrproc_t) xdr_exports, (caddr_t) &exportlist,
>>             total_timeout);
>> +        if (clnt_stat == RPC_PROGVERSMISMATCH) {
>> +            if (++vers <  max_vers)
>> +                goto again;
>> +        }
> 
> clnt_create(3t) should tell you if the requested version number is
> working; libtirpc's version does a NULLPROC call, for example.  It would
> be simpler to move this check into nfs_get_mount_client(), then you
> wouldn't need the retry loop here.
clnt_create() does not fail.. the clnt_call() does.. 

> 
> But nfs_get_mount_client() already doesn't care why the clnt_create(3t)
> call fails, it just retries the creation with different parameters if it
> didn't succeed.  Do we really care enough to retry _only_ if the
> specific RPC version isn't available?  We use the same procedure number
> with the same arguments and the same results for all three protocol
> versions, yes?
Let not make a mountain out of mole hill... the goal of this patch is stop using the lower mount protocol version so server can only support v3 and v4... nothing
more... 


steved.

Re: [PATCH] showmount: try v3 before falling back to v1

[Steve Dickson]

Revised patch incorporating the code review comments... 

steved. 

commit a96b79f57f49ce5b4d05b6b9da79bdec03b13764
Author: Steve Dickson <steved@redhat.com>
Date:   Tue Jan 5 15:39:00 2010 -0500

    showmount: Try the highest mount version then fall back to lower ones
    
    Showmount should try the highest mount version first then fall
    back to the lower ones when the server returns a RPC_PROGVERSMISMATCH
    error. The idea being not using the lower mount versions will begin
    the process of moving away from NFSv2 support.
    
    Signed-off-by: Steve Dickson <steved@redhat.com>

diff --git a/utils/showmount/showmount.c b/utils/showmount/showmount.c
index 418e8b9..74cf116 100644
--- a/utils/showmount/showmount.c
+++ b/utils/showmount/showmount.c
@@ -78,29 +78,36 @@ static void usage(FILE *fp, int n)
 	exit(n);
 }
 
-static const char *nfs_sm_pgmtbl[] = {
+static const char *mount_pgm_tbl[] = {
 	"showmount",
 	"mount",
 	"mountd",
 	NULL,
 };
 
+static const rpcvers_t mount_vers_tbl[] = {
+	MOUNTVERS_NFSV3,
+	MOUNTVERS_POSIX,
+	MOUNTVERS,
+};
+static const int max_vers_tblsz = 
+	(sizeof(mount_vers_tbl)/sizeof(mount_vers_tbl[0]));
+
 /*
  * Generate an RPC client handle connected to the mountd service
  * at @hostname, or die trying.
  *
  * Supports both AF_INET and AF_INET6 server addresses.
  */
-static CLIENT *nfs_get_mount_client(const char *hostname)
+static CLIENT *nfs_get_mount_client(const char *hostname, rpcvers_t vers)
 {
-	rpcprog_t program = nfs_getrpcbyname(MOUNTPROG, nfs_sm_pgmtbl);
+	rpcprog_t program = nfs_getrpcbyname(MOUNTPROG, mount_pgm_tbl);
 	CLIENT *client;
 
-	client = clnt_create(hostname, program, MOUNTVERS, "tcp");
+	client = clnt_create(hostname, program, vers, "tcp");
 	if (client)
 		return client;
-
-	client = clnt_create(hostname, program, MOUNTVERS, "udp");
+	client = clnt_create(hostname, program, vers, "udp");
 	if (client)
 		return client;
 
@@ -123,6 +130,7 @@ int main(int argc, char **argv)
 	int i;
 	int n;
 	int maxlen;
+	int unsigned vers=0;
 	char **dumpv;
 
 	program_name = argv[0];
@@ -185,7 +193,8 @@ int main(int argc, char **argv)
 		break;
 	}
 
-	mclient = nfs_get_mount_client(hostname);
+again:
+	mclient = nfs_get_mount_client(hostname, mount_vers_tbl[vers]);
 	mclient->cl_auth = authunix_create_default();
 	total_timeout.tv_sec = TOTAL_TIMEOUT;
 	total_timeout.tv_usec = 0;
@@ -197,6 +206,10 @@ int main(int argc, char **argv)
 			(xdrproc_t) xdr_void, NULL,
 			(xdrproc_t) xdr_exports, (caddr_t) &exportlist,
 			total_timeout);
+		if (clnt_stat == RPC_PROGVERSMISMATCH) {
+			if (++vers <  max_vers_tblsz)
+				goto again;
+		}
 		if (clnt_stat != RPC_SUCCESS) {
 			clnt_perror(mclient, "rpc mount export");
 			clnt_destroy(mclient);
@@ -232,6 +245,10 @@ int main(int argc, char **argv)
 		(xdrproc_t) xdr_void, NULL,
 		(xdrproc_t) xdr_mountlist, (caddr_t) &dumplist,
 		total_timeout);
+	if (clnt_stat == RPC_PROGVERSMISMATCH) {
+		if (++vers <  max_vers_tblsz)
+			goto again;
+	}
 	if (clnt_stat != RPC_SUCCESS) {
 		clnt_perror(mclient, "rpc mount dump");
 		clnt_destroy(mclient);

Re: [PATCH] showmount: try v3 before falling back to v1

[Dan McGee]

On Tue, Jan 5, 2010 at 2:38 PM, Steve Dickson <SteveD@redhat.com> wrote=
:
> On 01/05/2010 02:23 PM, Chuck Lever wrote:
>>>
>>> Author: Steve Dickson <steved@redhat.com>
>>> Date: =C2=A0 Tue Jan 5 13:29:07 2010 -0500
>>>
>>> =C2=A0 =C2=A0showmount: Try the highest mount version then fall bac=
k to lower ones
>>>
>>> =C2=A0 =C2=A0Showmount should try the highest mount version first t=
hen fall
>>> =C2=A0 =C2=A0back to the lower ones when the server returns a RPC_P=
ROGVERSMISMATCH
>>> =C2=A0 =C2=A0error. The idea being not using the lower mount versio=
ns will begin
>>> =C2=A0 =C2=A0the process of moving away from NFSv2 support.
>>>
>>> =C2=A0 =C2=A0Signed-off-by: Steve Dickson <steved@redhat.com>
>>>
>>> diff --git a/utils/showmount/showmount.c b/utils/showmount/showmoun=
t.c
>>> index 418e8b9..17224a6 100644
>>> --- a/utils/showmount/showmount.c
>>> +++ b/utils/showmount/showmount.c
>>> @@ -85,22 +85,29 @@ static const char *nfs_sm_pgmtbl[] =3D {
>>> =C2=A0 =C2=A0 NULL,
>>> };
>>>
>>> +static const int mount_vers[] =3D {
>>
>> RPC version numbers are rpcvers_t, not int.
> True..
>
>>
>> The array above this one is called "nfs_sm_pgmtbl"... to be consiste=
nt
>> with existing code you should name this one "nfs_sm_verstbl".
>>
>>> + =C2=A0 =C2=A0MOUNTVERS_NFSV3,
>>> + =C2=A0 =C2=A0MOUNTVERS_POSIX,
>>> + =C2=A0 =C2=A0MOUNTVERS,
>>> +};
>>> +static const int max_vers =3D (sizeof(mount_vers)/sizeof(mount_ver=
s[0]));
>>
>> Array indices are unsigned.
> Sure...
>
>>
>> Calling this "max_vers" suggests it's actually a version number, and=
 not
>> an index into the version array; that's confusing.
> Its pretty simple code.. don't see this confusion.... but..
> It changed to =C2=A0mount_vers_tbl
>>
>> The array above this one has a NULL entry as it's final element. =C2=
=A0To be
>> consistent with existing code, you should copy that logic for this a=
rray
>> instead of using a separate "max_vers" variable.
> Having the NULL messes up the sizeof calculations
>
>>
>>> +
>>> /*
>>> =C2=A0* Generate an RPC client handle connected to the mountd servi=
ce
>>> =C2=A0* at @hostname, or die trying.
>>> =C2=A0*
>>> =C2=A0* Supports both AF_INET and AF_INET6 server addresses.
>>> =C2=A0*/
>>> -static CLIENT *nfs_get_mount_client(const char *hostname)
>>> +static CLIENT *nfs_get_mount_client(const char *hostname, int vers=
)
>>
>> RPC version numbers are rpcvers_t, not int. =C2=A0At the very least,
>> clnt_create(3t) takes an unsigned version number argument.
>>
>>> {
>>> =C2=A0 =C2=A0 rpcprog_t program =3D nfs_getrpcbyname(MOUNTPROG, nfs=
_sm_pgmtbl);
>>> =C2=A0 =C2=A0 CLIENT *client;
>>>
>>> - =C2=A0 =C2=A0client =3D clnt_create(hostname, program, MOUNTVERS,=
 "tcp");
>>> + =C2=A0 =C2=A0client =3D clnt_create(hostname, program, vers, "tcp=
");
>>> =C2=A0 =C2=A0 if (client)
>>> =C2=A0 =C2=A0 =C2=A0 =C2=A0 return client;
>>>
>>> - =C2=A0 =C2=A0client =3D clnt_create(hostname, program, MOUNTVERS,=
 "udp");
>>> + =C2=A0 =C2=A0client =3D clnt_create(hostname, program, vers, "udp=
");
>>> =C2=A0 =C2=A0 if (client)
>>> =C2=A0 =C2=A0 =C2=A0 =C2=A0 return client;
>>>
>>> @@ -122,7 +129,7 @@ int main(int argc, char **argv)
>>> =C2=A0 =C2=A0 mountlist list;
>>> =C2=A0 =C2=A0 int i;
>>> =C2=A0 =C2=A0 int n;
>>> - =C2=A0 =C2=A0int maxlen;
>>> + =C2=A0 =C2=A0int maxlen, vers=3D0;
>>
>> Array indices are unsigned integers.
>>
>> Calling this "vers" suggests it's actually a version number, and not=
 an
>> index into the version array; that's confusing.
> and an index call 'j' or 'i' is descriptive?? vers is clear enough im=
ho...
>
>>
>>> =C2=A0 =C2=A0 char **dumpv;
>>>
>>> =C2=A0 =C2=A0 program_name =3D argv[0];
>>> @@ -185,7 +192,8 @@ int main(int argc, char **argv)
>>> =C2=A0 =C2=A0 =C2=A0 =C2=A0 break;
>>> =C2=A0 =C2=A0 }
>>>
>>> - =C2=A0 =C2=A0mclient =3D nfs_get_mount_client(hostname);
>>> +again:
>>> + =C2=A0 =C2=A0mclient =3D nfs_get_mount_client(hostname, mount_ver=
s[vers]);
>>> =C2=A0 =C2=A0 mclient->cl_auth =3D authunix_create_default();
>>> =C2=A0 =C2=A0 total_timeout.tv_sec =3D TOTAL_TIMEOUT;
>>> =C2=A0 =C2=A0 total_timeout.tv_usec =3D 0;
>>> @@ -197,6 +205,10 @@ int main(int argc, char **argv)
>>> =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 (xdrproc_t) xdr_void, NUL=
L,
>>> =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 (xdrproc_t) xdr_exports, =
(caddr_t) &exportlist,
>>> =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 total_timeout);
>>> + =C2=A0 =C2=A0 =C2=A0 =C2=A0if (clnt_stat =3D=3D RPC_PROGVERSMISMA=
TCH) {
>>> + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0if (++vers < =C2=A0max_v=
ers)
>>> + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0goto again=
;
>>> + =C2=A0 =C2=A0 =C2=A0 =C2=A0}
>>
>> clnt_create(3t) should tell you if the requested version number is
>> working; libtirpc's version does a NULLPROC call, for example. =C2=A0=
It would
>> be simpler to move this check into nfs_get_mount_client(), then you
>> wouldn't need the retry loop here.
> clnt_create() does not fail.. the clnt_call() does..
>
>>
>> But nfs_get_mount_client() already doesn't care why the clnt_create(=
3t)
>> call fails, it just retries the creation with different parameters i=
f it
>> didn't succeed. =C2=A0Do we really care enough to retry _only_ if th=
e
>> specific RPC version isn't available? =C2=A0We use the same procedur=
e number
>> with the same arguments and the same results for all three protocol
>> versions, yes?
> Let not make a mountain out of mole hill... the goal of this patch is=
 stop using the lower mount protocol version so server can only support=
 v3 and v4... nothing
> more...

As a side note, I don't care what gets accepted as long as it works
with modern versions of NFS. Let me know if you need anything more
from me, but I'm glad I got the discussion going.

-Dan

Re: [PATCH] showmount: try v3 before falling back to v1

[Chuck Lever]

On Jan 5, 2010, at 3:41 PM, Steve Dickson wrote:

> Revised patch incorporating the code review comments...
>
> steved.
>
> commit a96b79f57f49ce5b4d05b6b9da79bdec03b13764
> Author: Steve Dickson <steved@redhat.com>
> Date:   Tue Jan 5 15:39:00 2010 -0500
>
>    showmount: Try the highest mount version then fall back to lower  
> ones
>
>    Showmount should try the highest mount version first then fall
>    back to the lower ones when the server returns a  
> RPC_PROGVERSMISMATCH
>    error. The idea being not using the lower mount versions will begin
>    the process of moving away from NFSv2 support.
>
>    Signed-off-by: Steve Dickson <steved@redhat.com>
>
> diff --git a/utils/showmount/showmount.c b/utils/showmount/showmount.c
> index 418e8b9..74cf116 100644
> --- a/utils/showmount/showmount.c
> +++ b/utils/showmount/showmount.c
> @@ -78,29 +78,36 @@ static void usage(FILE *fp, int n)
> 	exit(n);
> }
>
> -static const char *nfs_sm_pgmtbl[] = {
> +static const char *mount_pgm_tbl[] = {
> 	"showmount",
> 	"mount",
> 	"mountd",
> 	NULL,
> };
>
> +static const rpcvers_t mount_vers_tbl[] = {
> +	MOUNTVERS_NFSV3,
> +	MOUNTVERS_POSIX,
> +	MOUNTVERS,
> +};
> +static const int max_vers_tblsz =
> +	(sizeof(mount_vers_tbl)/sizeof(mount_vers_tbl[0]));
> +
> /*
>  * Generate an RPC client handle connected to the mountd service
>  * at @hostname, or die trying.
>  *
>  * Supports both AF_INET and AF_INET6 server addresses.
>  */
> -static CLIENT *nfs_get_mount_client(const char *hostname)
> +static CLIENT *nfs_get_mount_client(const char *hostname, rpcvers_t  
> vers)
> {
> -	rpcprog_t program = nfs_getrpcbyname(MOUNTPROG, nfs_sm_pgmtbl);
> +	rpcprog_t program = nfs_getrpcbyname(MOUNTPROG, mount_pgm_tbl);
> 	CLIENT *client;
>
> -	client = clnt_create(hostname, program, MOUNTVERS, "tcp");
> +	client = clnt_create(hostname, program, vers, "tcp");
> 	if (client)
> 		return client;
> -
> -	client = clnt_create(hostname, program, MOUNTVERS, "udp");
> +	client = clnt_create(hostname, program, vers, "udp");
> 	if (client)
> 		return client;
>
> @@ -123,6 +130,7 @@ int main(int argc, char **argv)
> 	int i;
> 	int n;
> 	int maxlen;
> +	int unsigned vers=0;
> 	char **dumpv;
>
> 	program_name = argv[0];
> @@ -185,7 +193,8 @@ int main(int argc, char **argv)
> 		break;
> 	}
>
> -	mclient = nfs_get_mount_client(hostname);
> +again:
> +	mclient = nfs_get_mount_client(hostname, mount_vers_tbl[vers]);
> 	mclient->cl_auth = authunix_create_default();
> 	total_timeout.tv_sec = TOTAL_TIMEOUT;
> 	total_timeout.tv_usec = 0;
> @@ -197,6 +206,10 @@ int main(int argc, char **argv)
> 			(xdrproc_t) xdr_void, NULL,
> 			(xdrproc_t) xdr_exports, (caddr_t) &exportlist,
> 			total_timeout);
> +		if (clnt_stat == RPC_PROGVERSMISMATCH) {
> +			if (++vers <  max_vers_tblsz)
> +				goto again;
> +		}

If you're going to do this, you should destroy the clnt before  
retrying.  Better yet you can use CLNT_CONTROL() to change the RPC  
version of the clnt on the fly... that way you don't have to destroy  
the clnt and create a new one, which has to try creating both "tcp"  
and "udp" in some cases, making for a long timeout each time if the  
server doesn't support "tcp".

My preference however, is to do the simple thing, and use  
clnt_create_vers(3t) in nfs_get_mount_client().  AFAICT you wouldn't  
need any of this extra logic or the new table.

> 		if (clnt_stat != RPC_SUCCESS) {
> 			clnt_perror(mclient, "rpc mount export");
> 			clnt_destroy(mclient);
> @@ -232,6 +245,10 @@ int main(int argc, char **argv)
> 		(xdrproc_t) xdr_void, NULL,
> 		(xdrproc_t) xdr_mountlist, (caddr_t) &dumplist,
> 		total_timeout);
> +	if (clnt_stat == RPC_PROGVERSMISMATCH) {
> +		if (++vers <  max_vers_tblsz)
> +			goto again;
> +	}
> 	if (clnt_stat != RPC_SUCCESS) {
> 		clnt_perror(mclient, "rpc mount dump");
> 		clnt_destroy(mclient);
>
> --
> To unsubscribe from this list: send the line "unsubscribe linux-nfs"  
> in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html

-- 
Chuck Lever
chuck[dot]lever[at]oracle[dot]com

Re: [PATCH] showmount: try v3 before falling back to v1

[Steve Dickson]

On 01/05/2010 05:31 PM, Chuck Lever wrote:
> 
> On Jan 5, 2010, at 3:41 PM, Steve Dickson wrote:
> 
>> Revised patch incorporating the code review comments...
>>
>> steved.
>>
>> commit a96b79f57f49ce5b4d05b6b9da79bdec03b13764
>> Author: Steve Dickson <steved@redhat.com>
>> Date:   Tue Jan 5 15:39:00 2010 -0500
>>
>>    showmount: Try the highest mount version then fall back to lower ones
>>
>>    Showmount should try the highest mount version first then fall
>>    back to the lower ones when the server returns a RPC_PROGVERSMISMATCH
>>    error. The idea being not using the lower mount versions will begin
>>    the process of moving away from NFSv2 support.
>>
>>    Signed-off-by: Steve Dickson <steved@redhat.com>
>>
>> diff --git a/utils/showmount/showmount.c b/utils/showmount/showmount.c
>> index 418e8b9..74cf116 100644
>> --- a/utils/showmount/showmount.c
>> +++ b/utils/showmount/showmount.c
>> @@ -78,29 +78,36 @@ static void usage(FILE *fp, int n)
>>     exit(n);
>> }
>>
>> -static const char *nfs_sm_pgmtbl[] = {
>> +static const char *mount_pgm_tbl[] = {
>>     "showmount",
>>     "mount",
>>     "mountd",
>>     NULL,
>> };
>>
>> +static const rpcvers_t mount_vers_tbl[] = {
>> +    MOUNTVERS_NFSV3,
>> +    MOUNTVERS_POSIX,
>> +    MOUNTVERS,
>> +};
>> +static const int max_vers_tblsz =
>> +    (sizeof(mount_vers_tbl)/sizeof(mount_vers_tbl[0]));
>> +
>> /*
>>  * Generate an RPC client handle connected to the mountd service
>>  * at @hostname, or die trying.
>>  *
>>  * Supports both AF_INET and AF_INET6 server addresses.
>>  */
>> -static CLIENT *nfs_get_mount_client(const char *hostname)
>> +static CLIENT *nfs_get_mount_client(const char *hostname, rpcvers_t
>> vers)
>> {
>> -    rpcprog_t program = nfs_getrpcbyname(MOUNTPROG, nfs_sm_pgmtbl);
>> +    rpcprog_t program = nfs_getrpcbyname(MOUNTPROG, mount_pgm_tbl);
>>     CLIENT *client;
>>
>> -    client = clnt_create(hostname, program, MOUNTVERS, "tcp");
>> +    client = clnt_create(hostname, program, vers, "tcp");
>>     if (client)
>>         return client;
>> -
>> -    client = clnt_create(hostname, program, MOUNTVERS, "udp");
>> +    client = clnt_create(hostname, program, vers, "udp");
>>     if (client)
>>         return client;
>>
>> @@ -123,6 +130,7 @@ int main(int argc, char **argv)
>>     int i;
>>     int n;
>>     int maxlen;
>> +    int unsigned vers=0;
>>     char **dumpv;
>>
>>     program_name = argv[0];
>> @@ -185,7 +193,8 @@ int main(int argc, char **argv)
>>         break;
>>     }
>>
>> -    mclient = nfs_get_mount_client(hostname);
>> +again:
>> +    mclient = nfs_get_mount_client(hostname, mount_vers_tbl[vers]);
>>     mclient->cl_auth = authunix_create_default();
>>     total_timeout.tv_sec = TOTAL_TIMEOUT;
>>     total_timeout.tv_usec = 0;
>> @@ -197,6 +206,10 @@ int main(int argc, char **argv)
>>             (xdrproc_t) xdr_void, NULL,
>>             (xdrproc_t) xdr_exports, (caddr_t) &exportlist,
>>             total_timeout);
>> +        if (clnt_stat == RPC_PROGVERSMISMATCH) {
>> +            if (++vers <  max_vers_tblsz)
>> +                goto again;
>> +        }
> 
> If you're going to do this, you should destroy the clnt before
> retrying.  Better yet you can use CLNT_CONTROL() to change the RPC
> version of the clnt on the fly... that way you don't have to destroy the
> clnt and create a new one, which has to try creating both "tcp" and
> "udp" in some cases, making for a long timeout each time if the server
> doesn't support "tcp".
This is a very short lived command and 99.9% of the time this code will
not executed... so I guess I was not too worried about opening a couple
extra fd in the every unlikely case a server does not support v3... 

> 
> My preference however, is to do the simple thing, and use
> clnt_create_vers(3t) in nfs_get_mount_client().  AFAICT you wouldn't
> need any of this extra logic or the new table.
Yes I saw clnt_create_vers()... but I thought staying backwards
compatible with the glibc was a better idea... 

steved. 

Re: [PATCH] showmount: try v3 before falling back to v1

[Chuck Lever]

On Jan 5, 2010, at 6:24 PM, Steve Dickson wrote:

> On 01/05/2010 05:31 PM, Chuck Lever wrote:
>>
>> On Jan 5, 2010, at 3:41 PM, Steve Dickson wrote:
>>
>>> Revised patch incorporating the code review comments...
>>>
>>> steved.
>>>
>>> commit a96b79f57f49ce5b4d05b6b9da79bdec03b13764
>>> Author: Steve Dickson <steved@redhat.com>
>>> Date:   Tue Jan 5 15:39:00 2010 -0500
>>>
>>>   showmount: Try the highest mount version then fall back to lower  
>>> ones
>>>
>>>   Showmount should try the highest mount version first then fall
>>>   back to the lower ones when the server returns a  
>>> RPC_PROGVERSMISMATCH
>>>   error. The idea being not using the lower mount versions will  
>>> begin
>>>   the process of moving away from NFSv2 support.
>>>
>>>   Signed-off-by: Steve Dickson <steved@redhat.com>
>>>
>>> diff --git a/utils/showmount/showmount.c b/utils/showmount/ 
>>> showmount.c
>>> index 418e8b9..74cf116 100644
>>> --- a/utils/showmount/showmount.c
>>> +++ b/utils/showmount/showmount.c
>>> @@ -78,29 +78,36 @@ static void usage(FILE *fp, int n)
>>>    exit(n);
>>> }
>>>
>>> -static const char *nfs_sm_pgmtbl[] = {
>>> +static const char *mount_pgm_tbl[] = {
>>>    "showmount",
>>>    "mount",
>>>    "mountd",
>>>    NULL,
>>> };
>>>
>>> +static const rpcvers_t mount_vers_tbl[] = {
>>> +    MOUNTVERS_NFSV3,
>>> +    MOUNTVERS_POSIX,
>>> +    MOUNTVERS,
>>> +};
>>> +static const int max_vers_tblsz =
>>> +    (sizeof(mount_vers_tbl)/sizeof(mount_vers_tbl[0]));
>>> +
>>> /*
>>> * Generate an RPC client handle connected to the mountd service
>>> * at @hostname, or die trying.
>>> *
>>> * Supports both AF_INET and AF_INET6 server addresses.
>>> */
>>> -static CLIENT *nfs_get_mount_client(const char *hostname)
>>> +static CLIENT *nfs_get_mount_client(const char *hostname, rpcvers_t
>>> vers)
>>> {
>>> -    rpcprog_t program = nfs_getrpcbyname(MOUNTPROG, nfs_sm_pgmtbl);
>>> +    rpcprog_t program = nfs_getrpcbyname(MOUNTPROG, mount_pgm_tbl);
>>>    CLIENT *client;
>>>
>>> -    client = clnt_create(hostname, program, MOUNTVERS, "tcp");
>>> +    client = clnt_create(hostname, program, vers, "tcp");
>>>    if (client)
>>>        return client;
>>> -
>>> -    client = clnt_create(hostname, program, MOUNTVERS, "udp");
>>> +    client = clnt_create(hostname, program, vers, "udp");
>>>    if (client)
>>>        return client;
>>>
>>> @@ -123,6 +130,7 @@ int main(int argc, char **argv)
>>>    int i;
>>>    int n;
>>>    int maxlen;
>>> +    int unsigned vers=0;
>>>    char **dumpv;
>>>
>>>    program_name = argv[0];
>>> @@ -185,7 +193,8 @@ int main(int argc, char **argv)
>>>        break;
>>>    }
>>>
>>> -    mclient = nfs_get_mount_client(hostname);
>>> +again:
>>> +    mclient = nfs_get_mount_client(hostname, mount_vers_tbl[vers]);
>>>    mclient->cl_auth = authunix_create_default();
>>>    total_timeout.tv_sec = TOTAL_TIMEOUT;
>>>    total_timeout.tv_usec = 0;
>>> @@ -197,6 +206,10 @@ int main(int argc, char **argv)
>>>            (xdrproc_t) xdr_void, NULL,
>>>            (xdrproc_t) xdr_exports, (caddr_t) &exportlist,
>>>            total_timeout);
>>> +        if (clnt_stat == RPC_PROGVERSMISMATCH) {
>>> +            if (++vers <  max_vers_tblsz)
>>> +                goto again;
>>> +        }
>>
>> If you're going to do this, you should destroy the clnt before
>> retrying.  Better yet you can use CLNT_CONTROL() to change the RPC
>> version of the clnt on the fly... that way you don't have to  
>> destroy the
>> clnt and create a new one, which has to try creating both "tcp" and
>> "udp" in some cases, making for a long timeout each time if the  
>> server
>> doesn't support "tcp".
> This is a very short lived command and 99.9% of the time this code  
> will
> not executed... so I guess I was not too worried about opening a  
> couple
> extra fd in the every unlikely case a server does not support v3...

Dude, come on.  How hard is it to add two extra clnt_destroy(3) calls?

What about the potential for additional hangs during retries when  
neither v3 nor TCP is supported?  CLNT_CONTROL() would allow you to  
create the client once, and then reuse it.  I can send you a patch on  
top of this one that does that.

--
Chuck Lever
chuck[dot]lever[at]oracle[dot]com

Re: [PATCH] showmount: try v3 before falling back to v1

[Steve Dickson]

Addressed the not freeing of the client handle when the RPC_PROGVERSMISMATCH
error occurs. Also discovered there no hang when the server does not 
support TCP connections due to the fact the clnt_create() quires the
server on what transports are supported... 

steved.


Author: Steve Dickson <steved@redhat.com>
Date:   Thu Jan 7 11:30:03 2010 -0500

    showmount: Try the highest mount version then fall back to lower ones
    
    Showmount should try the highest mount version first then fall
    back to the lower ones when the server returns a RPC_PROGVERSMISMATCH
    error. The idea being not using the lower mount versions will begin
    the process of moving away from NFSv2 support.
    
    Signed-off-by: Steve Dickson <steved@redhat.com>

diff --git a/utils/showmount/showmount.c b/utils/showmount/showmount.c
index 418e8b9..80fd47a 100644
--- a/utils/showmount/showmount.c
+++ b/utils/showmount/showmount.c
@@ -78,29 +78,36 @@ static void usage(FILE *fp, int n)
 	exit(n);
 }
 
-static const char *nfs_sm_pgmtbl[] = {
+static const char *mount_pgm_tbl[] = {
 	"showmount",
 	"mount",
 	"mountd",
 	NULL,
 };
 
+static const rpcvers_t mount_vers_tbl[] = {
+	MOUNTVERS_NFSV3,
+	MOUNTVERS_POSIX,
+	MOUNTVERS,
+};
+static const int max_vers_tblsz = 
+	(sizeof(mount_vers_tbl)/sizeof(mount_vers_tbl[0]));
+
 /*
  * Generate an RPC client handle connected to the mountd service
  * at @hostname, or die trying.
  *
  * Supports both AF_INET and AF_INET6 server addresses.
  */
-static CLIENT *nfs_get_mount_client(const char *hostname)
+static CLIENT *nfs_get_mount_client(const char *hostname, rpcvers_t vers)
 {
-	rpcprog_t program = nfs_getrpcbyname(MOUNTPROG, nfs_sm_pgmtbl);
+	rpcprog_t program = nfs_getrpcbyname(MOUNTPROG, mount_pgm_tbl);
 	CLIENT *client;
 
-	client = clnt_create(hostname, program, MOUNTVERS, "tcp");
+	client = clnt_create(hostname, program, vers, "tcp");
 	if (client)
 		return client;
-
-	client = clnt_create(hostname, program, MOUNTVERS, "udp");
+	client = clnt_create(hostname, program, vers, "udp");
 	if (client)
 		return client;
 
@@ -123,6 +130,7 @@ int main(int argc, char **argv)
 	int i;
 	int n;
 	int maxlen;
+	int unsigned vers=0;
 	char **dumpv;
 
 	program_name = argv[0];
@@ -185,7 +193,8 @@ int main(int argc, char **argv)
 		break;
 	}
 
-	mclient = nfs_get_mount_client(hostname);
+again:
+	mclient = nfs_get_mount_client(hostname, mount_vers_tbl[vers]);
 	mclient->cl_auth = authunix_create_default();
 	total_timeout.tv_sec = TOTAL_TIMEOUT;
 	total_timeout.tv_usec = 0;
@@ -197,6 +206,12 @@ int main(int argc, char **argv)
 			(xdrproc_t) xdr_void, NULL,
 			(xdrproc_t) xdr_exports, (caddr_t) &exportlist,
 			total_timeout);
+		if (clnt_stat == RPC_PROGVERSMISMATCH) {
+			if (++vers <  max_vers_tblsz) {
+				clnt_destroy(mclient);
+				goto again;
+			}
+		}
 		if (clnt_stat != RPC_SUCCESS) {
 			clnt_perror(mclient, "rpc mount export");
 			clnt_destroy(mclient);
@@ -232,6 +247,12 @@ int main(int argc, char **argv)
 		(xdrproc_t) xdr_void, NULL,
 		(xdrproc_t) xdr_mountlist, (caddr_t) &dumplist,
 		total_timeout);
+	if (clnt_stat == RPC_PROGVERSMISMATCH) {
+		if (++vers <  max_vers_tblsz) {
+			clnt_destroy(mclient);
+			goto again;
+		}
+	}
 	if (clnt_stat != RPC_SUCCESS) {
 		clnt_perror(mclient, "rpc mount dump");
 		clnt_destroy(mclient);