Message-id: <171331463783.17212.6690111336952371965@noble.neil.brown.name>
Date: Wed, 17 Apr 2024 10:43:57 +1000
From: "NeilBrown" <neilb@...e.de>
To: "Jeff Layton" <jlayton@...nel.org>
Cc: "Lorenzo Bianconi" <lorenzo@...nel.org>, linux-nfs@...r.kernel.org,
 lorenzo.bianconi@...hat.com, chuck.lever@...cle.com, netdev@...r.kernel.org,
 kuba@...nel.org
Subject: Re: [PATCH v8 3/6] NFSD: add write_version to netlink command

On Wed, 17 Apr 2024, Jeff Layton wrote:
> On Wed, 2024-04-17 at 09:05 +1000, NeilBrown wrote:
> > On Wed, 17 Apr 2024, Jeff Layton wrote:
> > > On Wed, 2024-04-17 at 07:48 +1000, NeilBrown wrote:
> > > > On Tue, 16 Apr 2024, Jeff Layton wrote:
> > > > > On Tue, 2024-04-16 at 13:16 +1000, NeilBrown wrote:
> > > > > > On Tue, 16 Apr 2024, Lorenzo Bianconi wrote:
> > > > > > > Introduce write_version netlink command through a "declarative" interface.
> > > > > > > This patch introduces a change in behavior since for version-set userspace
> > > > > > > is expected to provide a NFS major/minor version list it wants to enable
> > > > > > > while all the other ones will be disabled. (procfs write_version
> > > > > > > command implements imperative interface where the admin writes +3/-3 to
> > > > > > > enable/disable a single version.
> > > > > > 
> > > > > > It seems a little weird to me that the interface always disables all
> > > > > > version, but then also allows individual versions to be disabled.
> > > > > > 
> > > > > > Would it be reasonable to simply ignore the "enabled" flag when setting
> > > > > > version, and just enable all versions listed??
> > > > > > 
> > > > > > Or maybe only enable those with the flag, and don't disable those
> > > > > > without the flag?
> > > > > > 
> > > > > > Those don't necessarily seem much better - but the current behaviour
> > > > > > still seems odd.
> > > > > > 
> > > > > 
> > > > > I think it makes sense.
> > > > > 
> > > > > We disable all versions, and enable any that have the "enabled" flag set
> > > > > in the call from userland. Userland technically needn't send down the
> > > > > versions that are disabled in the call, but the current userland program
> > > > > does.
> > > > > 
> > > > > I worry about imperative interfaces that might only say -- "enable v4.1,
> > > > > but disable v3" and leave the others in their current state. That
> > > > > requires that both the kernel and userland keep state about what
> > > > > versions are currently enabled and disabled, and it's possible to get
> > > > > that wrong.
> > > > 
> > > > I understand and support your aversion for imperative interfaces.
> > > > But this interface, as currently implemented, looks somewhat imperative.
> > > > The message sent to the kernel could enable some interfaces and then
> > > > disable them.  I know that isn't the intent, but it is what the code
> > > > supports.  Hence "weird".
> > > > 
> > > > We could add code to make that sort of thing impossible, but there isn't
> > > > much point.  Better to make it syntactically impossible.
> > > > 
> > > > Realistically there will never be NFSv4.3 as there is no need - new
> > > > features can be added incrementally. 
> > > > 
> > > 
> > > There is no need _so_far_. Who knows what the future will bring? Maybe
> > > we'll need v4.3 in order to add some needed feature?
> > > 
> > > >  So we could just pass an array of
> > > > 5 active flags: 2,3,4.0,4.1,4.2.  I suspect you wouldn't like that and
> > > > I'm not sure that I do either.  A "read" would return the same array
> > > > with 3 possible states: unavailable, disabled, enabled.  (Maybe the
> > > > array could be variable length so 5.0 could be added one day...).
> > > > 
> > > 
> > > A set of flags is basically what this interface is. They just happen to
> > > also be labeled with the major and minorversion. I think that's a good
> > > thing.
> > 
> > Good for whom?  Labelling allows for labelling inconsistencies.
> > 
> 
> Now you're just being silly. You wanted a variable length array, but
> what if the next slot is not v4.3 but 5.0? A positional interpretation
> of a slot in an array is just as just as subject to problems.

I don't think it could look like a imperative interface, which the
current one does a bit.

> 
> > Maybe the kernel should be able to provide an ordered list of labels,
> > and separately an array of which labels are enabled/disabled.
> > Userspace could send down a new set of enabled/disabled flags based on
> > the agreed set of labels.
> > 
> 
> How is this better than what's been proposed? One strength of netlink is
> that the data is structured. The already proposed interface takes
> advantage of that.
> 
> > Here is a question that is a bit of a diversion, but might help us
> > understand the context more fully:
> > 
> >   Why would anyone disable v4.2 separately from v4.1 ??
> > 
> 
> Furthermore, what does it mean to disable v4.1 but leave v4.2 enabled?

Indeed!

> 
> > I understand that v2, v3, v4.0, v4.1 are effectively different protocols
> > and you might want to ensure that only the approved/tested protocol is
> > used.  But v4.2 is just a few enhancements on v4.1.  Why would you want
> > to disable it?
> > 
> > The answer I can think of that there might be bugs (perish the
> > thought!!) in some of those features so you might want to avoid using
> > them.
> > But in that case, it is really the features that you want to suppress,
> > not the protocol version.
> > 
> > Maybe I might want to disable delegation - to just write delegation.
> > Can I do that?  What if I just want to disable server-side copy, but
> > keep fallocate and umask support?
> > 
> > i.e.  is a list of versions really the granularity that we want to use
> > for this interface?
> > 
> 
> Our current goal is to replace rpc.nfsd with a new program that works
> via netlink. An important bit of what rpc.nfsd does is start the NFS
> server with the settings in /etc/nfs.conf. Some of those settings are
> vers3=, vers4.0=, etc. that govern how /proc/fs/nfsd/versions is set.
> We have an immediate need to deal with those settings today, and
> probably will for quite some time.
> 
> I'm not opposed to augmenting that with something more granular, but I
> don't think we should block this interface and wait on that. We can
> extend the interface at some point in the future to take a new feature
> bitmask or something, and just declare that (e.g.) declaring vers4.2=n
> disables some subset of those features.

I agree that we don't want to block "good" while we wait for "perfect".  I
just want to be sure that what we have is "good".

The current /proc interface uses strings like "v3" and "v4.1".
The proposed netlink interface uses pairs on u32s - "major" and "minor".
So we lose some easy paths for extensibility.  Are we comfortable with
that?

This isn't a big deal - certainly not a blocked.  I just don't feel
entirely comfortable about the current interface and I'm exploring to
see if there might be something better.

Thanks,
NeilBrown


> 
> > 
> > > 
> > > > 
> > > > I haven't managed to come up with anything *better* than the current
> > > > proposal and I don't want to stand in its way, but I wanted to highlight
> > > > that it looks weird - as much imperative as declarative - in case
> > > > someone else might be able to come up with a better alternative.
> > > > 
> > > 
> > > The intention was to create a symmetrical interface. We have 2
> > > operations: a "get" that asks "what versions are currently supported and
> > > are they enabled?", and a "set" that says "here is the new state of
> > > version enablement".
> > > 
> > > The userland tool always sends down a complete set of versions. The
> > > kernel is (currently) more forgiving, and treats omitted versions as
> > > being disabled. The kernel could require that every supported version be
> > > represented in the "set" operation, if that's more desirable.
> > > 
> > > > > 
> > > > > My thinking was that by using a declarative interface like this, we
> > > > > eliminate ambiguity in how these interfaces are supposed to work. The
> > > > > client sends down an entire version map in one fell swoop, and we know
> > > > > exactly what the result should look like.
> > > > > 
> > > > > Note that you can enable or disable just a single version with the
> > > > > userland tool, but this way all of that complexity stays in userland.
> > > > > 
> > > > > > Also for getting the version, the doc says:
> > > > > > 
> > > > > >      doc: get nfs enabled versions
> > > > > > 
> > > > > > which I don't think it quite right.  The code reports all supported
> > > > > > versions, and indicates which of those are enabled.  So maybe:
> > > > > > 
> > > > > >      doc: get enabled status for all supported versions
> > > > > > 
> > > > > > 
> > > > > > I think that fact that it actually lists all supported versions is
> > > > > > useful and worth making explicit.
> > > > > > 
> > > > > > 
> > > > > 
> > > > > Agreed. We should make that change before merging anything.
> > > > > 
> > > > > > > 
> > > > > > > Reviewed-by: Jeff Layton <jlayton@...nel.org>
> > > > > > > Tested-by: Jeff Layton <jlayton@...nel.org>
> > > > > > > Signed-off-by: Lorenzo Bianconi <lorenzo@...nel.org>
> > > > > > > ---
> > > > > > >  Documentation/netlink/specs/nfsd.yaml |  37 +++++++
> > > > > > >  fs/nfsd/netlink.c                     |  24 +++++
> > > > > > >  fs/nfsd/netlink.h                     |   5 +
> > > > > > >  fs/nfsd/netns.h                       |   1 +
> > > > > > >  fs/nfsd/nfsctl.c                      | 150 ++++++++++++++++++++++++++
> > > > > > >  fs/nfsd/nfssvc.c                      |   3 +-
> > > > > > >  include/uapi/linux/nfsd_netlink.h     |  18 ++++
> > > > > > >  7 files changed, 236 insertions(+), 2 deletions(-)
> > > > > > > 
> > > > > > > diff --git a/Documentation/netlink/specs/nfsd.yaml b/Documentation/netlink/specs/nfsd.yaml
> > > > > > > index cbe6c5fd6c4d..0396e8b3ea1f 100644
> > > > > > > --- a/Documentation/netlink/specs/nfsd.yaml
> > > > > > > +++ b/Documentation/netlink/specs/nfsd.yaml
> > > > > > > @@ -74,6 +74,26 @@ attribute-sets:
> > > > > > >        -
> > > > > > >          name: leasetime
> > > > > > >          type: u32
> > > > > > > +  -
> > > > > > > +    name: version
> > > > > > > +    attributes:
> > > > > > > +      -
> > > > > > > +        name: major
> > > > > > > +        type: u32
> > > > > > > +      -
> > > > > > > +        name: minor
> > > > > > > +        type: u32
> > > > > > > +      -
> > > > > > > +        name: enabled
> > > > > > > +        type: flag
> > > > > > > +  -
> > > > > > > +    name: server-proto
> > > > > > > +    attributes:
> > > > > > > +      -
> > > > > > > +        name: version
> > > > > > > +        type: nest
> > > > > > > +        nested-attributes: version
> > > > > > > +        multi-attr: true
> > > > > > >  
> > > > > > >  operations:
> > > > > > >    list:
> > > > > > > @@ -120,3 +140,20 @@ operations:
> > > > > > >              - threads
> > > > > > >              - gracetime
> > > > > > >              - leasetime
> > > > > > > +    -
> > > > > > > +      name: version-set
> > > > > > > +      doc: set nfs enabled versions
> > > > > > > +      attribute-set: server-proto
> > > > > > > +      flags: [ admin-perm ]
> > > > > > > +      do:
> > > > > > > +        request:
> > > > > > > +          attributes:
> > > > > > > +            - version
> > > > > > > +    -
> > > > > > > +      name: version-get
> > > > > > > +      doc: get nfs enabled versions
> > > > > > > +      attribute-set: server-proto
> > > > > > > +      do:
> > > > > > > +        reply:
> > > > > > > +          attributes:
> > > > > > > +            - version
> > > > > > > diff --git a/fs/nfsd/netlink.c b/fs/nfsd/netlink.c
> > > > > > > index 20a646af0324..bf5df9597288 100644
> > > > > > > --- a/fs/nfsd/netlink.c
> > > > > > > +++ b/fs/nfsd/netlink.c
> > > > > > > @@ -10,6 +10,13 @@
> > > > > > >  
> > > > > > >  #include <uapi/linux/nfsd_netlink.h>
> > > > > > >  
> > > > > > > +/* Common nested types */
> > > > > > > +const struct nla_policy nfsd_version_nl_policy[NFSD_A_VERSION_ENABLED + 1] = {
> > > > > > > +	[NFSD_A_VERSION_MAJOR] = { .type = NLA_U32, },
> > > > > > > +	[NFSD_A_VERSION_MINOR] = { .type = NLA_U32, },
> > > > > > > +	[NFSD_A_VERSION_ENABLED] = { .type = NLA_FLAG, },
> > > > > > > +};
> > > > > > > +
> > > > > > >  /* NFSD_CMD_THREADS_SET - do */
> > > > > > >  static const struct nla_policy nfsd_threads_set_nl_policy[NFSD_A_SERVER_WORKER_LEASETIME + 1] = {
> > > > > > >  	[NFSD_A_SERVER_WORKER_THREADS] = { .type = NLA_U32, },
> > > > > > > @@ -17,6 +24,11 @@ static const struct nla_policy nfsd_threads_set_nl_policy[NFSD_A_SERVER_WORKER_L
> > > > > > >  	[NFSD_A_SERVER_WORKER_LEASETIME] = { .type = NLA_U32, },
> > > > > > >  };
> > > > > > >  
> > > > > > > +/* NFSD_CMD_VERSION_SET - do */
> > > > > > > +static const struct nla_policy nfsd_version_set_nl_policy[NFSD_A_SERVER_PROTO_VERSION + 1] = {
> > > > > > > +	[NFSD_A_SERVER_PROTO_VERSION] = NLA_POLICY_NESTED(nfsd_version_nl_policy),
> > > > > > > +};
> > > > > > > +
> > > > > > >  /* Ops table for nfsd */
> > > > > > >  static const struct genl_split_ops nfsd_nl_ops[] = {
> > > > > > >  	{
> > > > > > > @@ -38,6 +50,18 @@ static const struct genl_split_ops nfsd_nl_ops[] = {
> > > > > > >  		.doit	= nfsd_nl_threads_get_doit,
> > > > > > >  		.flags	= GENL_CMD_CAP_DO,
> > > > > > >  	},
> > > > > > > +	{
> > > > > > > +		.cmd		= NFSD_CMD_VERSION_SET,
> > > > > > > +		.doit		= nfsd_nl_version_set_doit,
> > > > > > > +		.policy		= nfsd_version_set_nl_policy,
> > > > > > > +		.maxattr	= NFSD_A_SERVER_PROTO_VERSION,
> > > > > > > +		.flags		= GENL_ADMIN_PERM | GENL_CMD_CAP_DO,
> > > > > > > +	},
> > > > > > > +	{
> > > > > > > +		.cmd	= NFSD_CMD_VERSION_GET,
> > > > > > > +		.doit	= nfsd_nl_version_get_doit,
> > > > > > > +		.flags	= GENL_CMD_CAP_DO,
> > > > > > > +	},
> > > > > > >  };
> > > > > > >  
> > > > > > >  struct genl_family nfsd_nl_family __ro_after_init = {
> > > > > > > diff --git a/fs/nfsd/netlink.h b/fs/nfsd/netlink.h
> > > > > > > index 4137fac477e4..c7c0da275481 100644
> > > > > > > --- a/fs/nfsd/netlink.h
> > > > > > > +++ b/fs/nfsd/netlink.h
> > > > > > > @@ -11,6 +11,9 @@
> > > > > > >  
> > > > > > >  #include <uapi/linux/nfsd_netlink.h>
> > > > > > >  
> > > > > > > +/* Common nested types */
> > > > > > > +extern const struct nla_policy nfsd_version_nl_policy[NFSD_A_VERSION_ENABLED + 1];
> > > > > > > +
> > > > > > >  int nfsd_nl_rpc_status_get_start(struct netlink_callback *cb);
> > > > > > >  int nfsd_nl_rpc_status_get_done(struct netlink_callback *cb);
> > > > > > >  
> > > > > > > @@ -18,6 +21,8 @@ int nfsd_nl_rpc_status_get_dumpit(struct sk_buff *skb,
> > > > > > >  				  struct netlink_callback *cb);
> > > > > > >  int nfsd_nl_threads_set_doit(struct sk_buff *skb, struct genl_info *info);
> > > > > > >  int nfsd_nl_threads_get_doit(struct sk_buff *skb, struct genl_info *info);
> > > > > > > +int nfsd_nl_version_set_doit(struct sk_buff *skb, struct genl_info *info);
> > > > > > > +int nfsd_nl_version_get_doit(struct sk_buff *skb, struct genl_info *info);
> > > > > > >  
> > > > > > >  extern struct genl_family nfsd_nl_family;
> > > > > > >  
> > > > > > > diff --git a/fs/nfsd/netns.h b/fs/nfsd/netns.h
> > > > > > > index d4be519b5734..14ec15656320 100644
> > > > > > > --- a/fs/nfsd/netns.h
> > > > > > > +++ b/fs/nfsd/netns.h
> > > > > > > @@ -218,6 +218,7 @@ struct nfsd_net {
> > > > > > >  /* Simple check to find out if a given net was properly initialized */
> > > > > > >  #define nfsd_netns_ready(nn) ((nn)->sessionid_hashtbl)
> > > > > > >  
> > > > > > > +extern bool nfsd_support_version(int vers);
> > > > > > >  extern void nfsd_netns_free_versions(struct nfsd_net *nn);
> > > > > > >  
> > > > > > >  extern unsigned int nfsd_net_id;
> > > > > > > diff --git a/fs/nfsd/nfsctl.c b/fs/nfsd/nfsctl.c
> > > > > > > index 38a5df03981b..2c8929ef79e9 100644
> > > > > > > --- a/fs/nfsd/nfsctl.c
> > > > > > > +++ b/fs/nfsd/nfsctl.c
> > > > > > > @@ -1757,6 +1757,156 @@ int nfsd_nl_threads_get_doit(struct sk_buff *skb, struct genl_info *info)
> > > > > > >  	return err;
> > > > > > >  }
> > > > > > >  
> > > > > > > +/**
> > > > > > > + * nfsd_nl_version_set_doit - set the nfs enabled versions
> > > > > > > + * @skb: reply buffer
> > > > > > > + * @info: netlink metadata and command arguments
> > > > > > > + *
> > > > > > > + * Return 0 on success or a negative errno.
> > > > > > > + */
> > > > > > > +int nfsd_nl_version_set_doit(struct sk_buff *skb, struct genl_info *info)
> > > > > > > +{
> > > > > > > +	const struct nlattr *attr;
> > > > > > > +	struct nfsd_net *nn;
> > > > > > > +	int i, rem;
> > > > > > > +
> > > > > > > +	if (GENL_REQ_ATTR_CHECK(info, NFSD_A_SERVER_PROTO_VERSION))
> > > > > > > +		return -EINVAL;
> > > > > > > +
> > > > > > > +	mutex_lock(&nfsd_mutex);
> > > > > > > +
> > > > > > > +	nn = net_generic(genl_info_net(info), nfsd_net_id);
> > > > > > > +	if (nn->nfsd_serv) {
> > > > > > > +		mutex_unlock(&nfsd_mutex);
> > > > > > > +		return -EBUSY;
> > > > > > > +	}
> > > > > > > +
> > > > > > > +	/* clear current supported versions. */
> > > > > > > +	nfsd_vers(nn, 2, NFSD_CLEAR);
> > > > > > > +	nfsd_vers(nn, 3, NFSD_CLEAR);
> > > > > > > +	for (i = 0; i <= NFSD_SUPPORTED_MINOR_VERSION; i++)
> > > > > > > +		nfsd_minorversion(nn, i, NFSD_CLEAR);
> > > > > > > +
> > > > > > > +	nlmsg_for_each_attr(attr, info->nlhdr, GENL_HDRLEN, rem) {
> > > > > > > +		struct nlattr *tb[NFSD_A_VERSION_MAX + 1];
> > > > > > > +		u32 major, minor = 0;
> > > > > > > +		bool enabled;
> > > > > > > +
> > > > > > > +		if (nla_type(attr) != NFSD_A_SERVER_PROTO_VERSION)
> > > > > > > +			continue;
> > > > > > > +
> > > > > > > +		if (nla_parse_nested(tb, NFSD_A_VERSION_MAX, attr,
> > > > > > > +				     nfsd_version_nl_policy, info->extack) < 0)
> > > > > > > +			continue;
> > > > > > > +
> > > > > > > +		if (!tb[NFSD_A_VERSION_MAJOR])
> > > > > > > +			continue;
> > > > > > > +
> > > > > > > +		major = nla_get_u32(tb[NFSD_A_VERSION_MAJOR]);
> > > > > > > +		if (tb[NFSD_A_VERSION_MINOR])
> > > > > > > +			minor = nla_get_u32(tb[NFSD_A_VERSION_MINOR]);
> > > > > > > +
> > > > > > > +		enabled = nla_get_flag(tb[NFSD_A_VERSION_ENABLED]);
> > > > > > > +
> > > > > > > +		switch (major) {
> > > > > > > +		case 4:
> > > > > > > +			nfsd_minorversion(nn, minor, enabled ? NFSD_SET : NFSD_CLEAR);
> > > > > > > +			break;
> > > > > > > +		case 3:
> > > > > > > +		case 2:
> > > > > > > +			if (!minor)
> > > > > > > +				nfsd_vers(nn, major, enabled ? NFSD_SET : NFSD_CLEAR);
> > > > > > > +			break;
> > > > > > > +		default:
> > > > > > > +			break;
> > > > > > > +		}
> > > > > > > +	}
> > > > > > > +
> > > > > > > +	mutex_unlock(&nfsd_mutex);
> > > > > > > +
> > > > > > > +	return 0;
> > > > > > > +}
> > > > > > > +
> > > > > > > +/**
> > > > > > > + * nfsd_nl_version_get_doit - get the nfs enabled versions
> > > > > > > + * @skb: reply buffer
> > > > > > > + * @info: netlink metadata and command arguments
> > > > > > > + *
> > > > > > > + * Return 0 on success or a negative errno.
> > > > > > > + */
> > > > > > > +int nfsd_nl_version_get_doit(struct sk_buff *skb, struct genl_info *info)
> > > > > > > +{
> > > > > > > +	struct nfsd_net *nn;
> > > > > > > +	int i, err;
> > > > > > > +	void *hdr;
> > > > > > > +
> > > > > > > +	skb = genlmsg_new(GENLMSG_DEFAULT_SIZE, GFP_KERNEL);
> > > > > > > +	if (!skb)
> > > > > > > +		return -ENOMEM;
> > > > > > > +
> > > > > > > +	hdr = genlmsg_iput(skb, info);
> > > > > > > +	if (!hdr) {
> > > > > > > +		err = -EMSGSIZE;
> > > > > > > +		goto err_free_msg;
> > > > > > > +	}
> > > > > > > +
> > > > > > > +	mutex_lock(&nfsd_mutex);
> > > > > > > +	nn = net_generic(genl_info_net(info), nfsd_net_id);
> > > > > > > +
> > > > > > > +	for (i = 2; i <= 4; i++) {
> > > > > > > +		int j;
> > > > > > > +
> > > > > > > +		for (j = 0; j <= NFSD_SUPPORTED_MINOR_VERSION; j++) {
> > > > > > > +			struct nlattr *attr;
> > > > > > > +
> > > > > > > +			/* Don't record any versions the kernel doesn't have
> > > > > > > +			 * compiled in
> > > > > > > +			 */
> > > > > > > +			if (!nfsd_support_version(i))
> > > > > > > +				continue;
> > > > > > > +
> > > > > > > +			/* NFSv{2,3} does not support minor numbers */
> > > > > > > +			if (i < 4 && j)
> > > > > > > +				continue;
> > > > > > > +
> > > > > > > +			attr = nla_nest_start(skb,
> > > > > > > +					      NFSD_A_SERVER_PROTO_VERSION);
> > > > > > > +			if (!attr) {
> > > > > > > +				err = -EINVAL;
> > > > > > > +				goto err_nfsd_unlock;
> > > > > > > +			}
> > > > > > > +
> > > > > > > +			if (nla_put_u32(skb, NFSD_A_VERSION_MAJOR, i) ||
> > > > > > > +			    nla_put_u32(skb, NFSD_A_VERSION_MINOR, j)) {
> > > > > > > +				err = -EINVAL;
> > > > > > > +				goto err_nfsd_unlock;
> > > > > > > +			}
> > > > > > > +
> > > > > > > +			/* Set the enabled flag if the version is enabled */
> > > > > > > +			if (nfsd_vers(nn, i, NFSD_TEST) &&
> > > > > > > +			    (i < 4 || nfsd_minorversion(nn, j, NFSD_TEST)) &&
> > > > > > > +			    nla_put_flag(skb, NFSD_A_VERSION_ENABLED)) {
> > > > > > > +				err = -EINVAL;
> > > > > > > +				goto err_nfsd_unlock;
> > > > > > > +			}
> > > > > > > +
> > > > > > > +			nla_nest_end(skb, attr);
> > > > > > > +		}
> > > > > > > +	}
> > > > > > > +
> > > > > > > +	mutex_unlock(&nfsd_mutex);
> > > > > > > +	genlmsg_end(skb, hdr);
> > > > > > > +
> > > > > > > +	return genlmsg_reply(skb, info);
> > > > > > > +
> > > > > > > +err_nfsd_unlock:
> > > > > > > +	mutex_unlock(&nfsd_mutex);
> > > > > > > +err_free_msg:
> > > > > > > +	nlmsg_free(skb);
> > > > > > > +
> > > > > > > +	return err;
> > > > > > > +}
> > > > > > > +
> > > > > > >  /**
> > > > > > >   * nfsd_net_init - Prepare the nfsd_net portion of a new net namespace
> > > > > > >   * @net: a freshly-created network namespace
> > > > > > > diff --git a/fs/nfsd/nfssvc.c b/fs/nfsd/nfssvc.c
> > > > > > > index ca193f7ff0e1..4fc91f50138a 100644
> > > > > > > --- a/fs/nfsd/nfssvc.c
> > > > > > > +++ b/fs/nfsd/nfssvc.c
> > > > > > > @@ -133,8 +133,7 @@ struct svc_program		nfsd_program = {
> > > > > > >  	.pg_rpcbind_set		= nfsd_rpcbind_set,
> > > > > > >  };
> > > > > > >  
> > > > > > > -static bool
> > > > > > > -nfsd_support_version(int vers)
> > > > > > > +bool nfsd_support_version(int vers)
> > > > > > >  {
> > > > > > >  	if (vers >= NFSD_MINVERS && vers < NFSD_NRVERS)
> > > > > > >  		return nfsd_version[vers] != NULL;
> > > > > > > diff --git a/include/uapi/linux/nfsd_netlink.h b/include/uapi/linux/nfsd_netlink.h
> > > > > > > index ccc78a5ee650..8a0a2b344923 100644
> > > > > > > --- a/include/uapi/linux/nfsd_netlink.h
> > > > > > > +++ b/include/uapi/linux/nfsd_netlink.h
> > > > > > > @@ -38,10 +38,28 @@ enum {
> > > > > > >  	NFSD_A_SERVER_WORKER_MAX = (__NFSD_A_SERVER_WORKER_MAX - 1)
> > > > > > >  };
> > > > > > >  
> > > > > > > +enum {
> > > > > > > +	NFSD_A_VERSION_MAJOR = 1,
> > > > > > > +	NFSD_A_VERSION_MINOR,
> > > > > > > +	NFSD_A_VERSION_ENABLED,
> > > > > > > +
> > > > > > > +	__NFSD_A_VERSION_MAX,
> > > > > > > +	NFSD_A_VERSION_MAX = (__NFSD_A_VERSION_MAX - 1)
> > > > > > > +};
> > > > > > > +
> > > > > > > +enum {
> > > > > > > +	NFSD_A_SERVER_PROTO_VERSION = 1,
> > > > > > > +
> > > > > > > +	__NFSD_A_SERVER_PROTO_MAX,
> > > > > > > +	NFSD_A_SERVER_PROTO_MAX = (__NFSD_A_SERVER_PROTO_MAX - 1)
> > > > > > > +};
> > > > > > > +
> > > > > > >  enum {
> > > > > > >  	NFSD_CMD_RPC_STATUS_GET = 1,
> > > > > > >  	NFSD_CMD_THREADS_SET,
> > > > > > >  	NFSD_CMD_THREADS_GET,
> > > > > > > +	NFSD_CMD_VERSION_SET,
> > > > > > > +	NFSD_CMD_VERSION_GET,
> > > > > > >  
> > > > > > >  	__NFSD_CMD_MAX,
> > > > > > >  	NFSD_CMD_MAX = (__NFSD_CMD_MAX - 1)
> > > > > > > -- 
> > > > > > > 2.44.0
> > > > > > > 
> > > > > > > 
> > > > > > 
> > > > > 
> > > > > -- 
> > > > > Jeff Layton <jlayton@...nel.org>
> > > > > 
> > > > 
> > > 
> > > -- 
> > > Jeff Layton <jlayton@...nel.org>
> > > 
> > 
> 
> -- 
> Jeff Layton <jlayton@...nel.org>
> 

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