[RFC PATCH net-next v2] ethtool: Improve compatibility between netlink and ioctl interfaces

From: Ido Schimmel <idosch@nvidia.com>

With the ioctl interface, when autoneg is enabled, but without
specifying speed, duplex or link modes, the advertised link modes are
set to the supported link modes by the ethtool user space utility.
Example:

# ethtool --version
ethtool version 5.4

# ethtool -s eth0 advertise 0xC autoneg on

# ethtool eth0
Settings for eth0:
        Supported ports: [ TP ]
        Supported link modes:   10baseT/Half 10baseT/Full
                                100baseT/Half 100baseT/Full
                                1000baseT/Full
        Supported pause frame use: No
        Supports auto-negotiation: Yes
        Supported FEC modes: Not reported
        Advertised link modes:  100baseT/Half 100baseT/Full
        Advertised pause frame use: No
        Advertised auto-negotiation: Yes
        Advertised FEC modes: Not reported
        Speed: 1000Mb/s
        Duplex: Full
        Port: Twisted Pair
        PHYAD: 0
        Transceiver: internal
        Auto-negotiation: on
        MDI-X: Unknown (auto)
        Supports Wake-on: umbg
        Wake-on: d
        Current message level: 0x00000007 (7)
                               drv probe link
        Link detected: no

# ethtool -s eth0 autoneg on

184 more lines

diff --git a/Documentation/networking/ethtool-netlink.rst b/Documentation/networking/ethtool-netlink.rst
index 30b98245979f..2993bcaa93ca 100644
--- a/Documentation/networking/ethtool-netlink.rst
+++ b/Documentation/networking/ethtool-netlink.rst

@@ -65,11 +65,12 @@ all devices providing it (each device in a separate message).
 types. The interpretation of these flags is the same for all request types but
 the flags may not apply to requests. Recognized flags are:
 
-  =================================  ===================================
+  =================================  =========================================
   ``ETHTOOL_FLAG_COMPACT_BITSETS``   use compact format bitsets in reply
   ``ETHTOOL_FLAG_OMIT_REPLY``        omit optional reply (_SET and _ACT)
   ``ETHTOOL_FLAG_STATS``             include optional device statistics
-  =================================  ===================================
+  ``ETHTOOL_FLAG_LEGACY``            be compatible with legacy ioctl interface
+  =================================  =========================================
 
 New request flags should follow the general idea that if the flag is not set,
 the behaviour is backward compatible, i.e. requests from old clients not aware

@@ -442,6 +443,10 @@ autoselection is done on ethtool side with ioctl interface, netlink interface
 is supposed to allow requesting changes without knowing what exactly kernel
 supports.
 
+If autonegotiation is on (either set now or kept from before), no other
+parameter is specified (e.g., speed) and ``ETHTOOL_FLAG_LEGACY`` flag is set,
+kernel adjusts advertised modes to all supported modes. This autoselection is
+done on ethtool side with ioctl interface.
 
 LINKSTATE_GET
 =============

diff --git a/include/uapi/linux/ethtool_netlink.h b/include/uapi/linux/ethtool_netlink.h
index e2bf36e6964b..923c2379ade6 100644
--- a/include/uapi/linux/ethtool_netlink.h
+++ b/include/uapi/linux/ethtool_netlink.h

@@ -94,10 +94,13 @@ enum {
 #define ETHTOOL_FLAG_OMIT_REPLY	(1 << 1)
 /* request statistics, if supported by the driver */
 #define ETHTOOL_FLAG_STATS		(1 << 2)
+/* be compatible with legacy ioctl interface */
+#define ETHTOOL_FLAG_LEGACY		(1 << 3)
 
 #define ETHTOOL_FLAG_ALL (ETHTOOL_FLAG_COMPACT_BITSETS | \
 			  ETHTOOL_FLAG_OMIT_REPLY | \
-			  ETHTOOL_FLAG_STATS)
+			  ETHTOOL_FLAG_STATS | \
+			  ETHTOOL_FLAG_LEGACY)
 
 enum {
 	ETHTOOL_A_HEADER_UNSPEC,

diff --git a/net/ethtool/linkmodes.c b/net/ethtool/linkmodes.c
index 29dcd675b65a..e5e70662cc8e 100644
--- a/net/ethtool/linkmodes.c
+++ b/net/ethtool/linkmodes.c

@@ -290,9 +290,9 @@ linkmodes_set_policy[ETHTOOL_A_LINKMODES_MAX + 1] = {
 };
 
 /* Set advertised link modes to all supported modes matching requested speed
- * and duplex values. Called when autonegotiation is on, speed or duplex is
- * requested but no link mode change. This is done in userspace with ioctl()
- * interface, move it into kernel for netlink.
+ * and duplex values, if specified. Called when autonegotiation is on, speed,
+ * duplex or legacy behavior is requested but no link mode change. This is done
+ * in userspace with ioctl() interface, move it into kernel for netlink.
  * Returns true if advertised modes bitmap was modified.
  */
 static bool ethnl_auto_linkmodes(struct ethtool_link_ksettings *ksettings,

@@ -340,7 +340,7 @@ static bool ethnl_validate_master_slave_cfg(u8 cfg)
 
 static int ethnl_update_linkmodes(struct genl_info *info, struct nlattr **tb,
 				  struct ethtool_link_ksettings *ksettings,
-				  bool *mod)
+				  bool req_legacy, bool *mod)
 {
 	struct ethtool_link_settings *lsettings = &ksettings->base;
 	bool req_speed, req_duplex;

@@ -383,7 +383,7 @@ static int ethnl_update_linkmodes(struct genl_info *info, struct nlattr **tb,
 	ethnl_update_u8(&lsettings->master_slave_cfg, master_slave_cfg, mod);
 
 	if (!tb[ETHTOOL_A_LINKMODES_OURS] && lsettings->autoneg &&
-	    (req_speed || req_duplex) &&
+	    (req_speed || req_duplex || req_legacy) &&
 	    ethnl_auto_linkmodes(ksettings, req_speed, req_duplex))
 		*mod = true;
 

@@ -397,6 +397,7 @@ int ethnl_set_linkmodes(struct sk_buff *skb, struct genl_info *info)
 	struct ethnl_req_info req_info = {};
 	struct net_device *dev;
 	bool mod = false;
+	bool req_legacy;
 	int ret;
 
 	ret = nlmsg_parse(info->nlhdr, GENL_HDRLEN, tb,

@@ -410,6 +411,7 @@ int ethnl_set_linkmodes(struct sk_buff *skb, struct genl_info *info)
 					 true);
 	if (ret < 0)
 		return ret;
+	req_legacy = req_info.flags & ETHTOOL_FLAG_LEGACY;
 	dev = req_info.dev;
 	ret = -EOPNOTSUPP;
 	if (!dev->ethtool_ops->get_link_ksettings ||

@@ -427,7 +429,7 @@ int ethnl_set_linkmodes(struct sk_buff *skb, struct genl_info *info)
 		goto out_ops;
 	}
 
-	ret = ethnl_update_linkmodes(info, tb, &ksettings, &mod);
+	ret = ethnl_update_linkmodes(info, tb, &ksettings, req_legacy, &mod);
 	if (ret < 0)
 		goto out_ops;
 

-- 
2.26.2

From: Ido Schimmel

Sent: 04 October 2020 11:17

With the ioctl interface, when autoneg is enabled, but without
specifying speed, duplex or link modes, the advertised link modes are
set to the supported link modes by the ethtool user space utility.

...

Fix this incompatibility problem by introducing a new flag in the
ethtool netlink request header: 'ETHTOOL_FLAG_LEGACY'. The purpose of
the flag is to indicate to the kernel that it needs to be compatible
with the legacy ioctl interface. A patch to the ethtool user space
utility will make sure the flag is always set.

You need to do that the other way around.
You can't assume the kernel and application are updated
at the same time.

	David

-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)

On Sun, Oct 04, 2020 at 12:46:31PM +0000, David Laight wrote:

From: Ido Schimmel

quoted

Sent: 04 October 2020 11:17

With the ioctl interface, when autoneg is enabled, but without
specifying speed, duplex or link modes, the advertised link modes are
set to the supported link modes by the ethtool user space utility.

...

quoted

Fix this incompatibility problem by introducing a new flag in the
ethtool netlink request header: 'ETHTOOL_FLAG_LEGACY'. The purpose of
the flag is to indicate to the kernel that it needs to be compatible
with the legacy ioctl interface. A patch to the ethtool user space
utility will make sure the flag is always set.

You need to do that the other way around.
You can't assume the kernel and application are updated
at the same time.

Thanks, David. In case ethtool is updated without updating the kernel we
will indeed get an error:

# ethtool -s eth0 autoneg on
netlink error: unrecognized request flags (offset 36)
netlink error: Operation not supported

Will wait for Michal's comments before doing another round.

On Sun, Oct 04, 2020 at 04:37:57PM +0300, Ido Schimmel wrote:

On Sun, Oct 04, 2020 at 12:46:31PM +0000, David Laight wrote:

quoted

From: Ido Schimmel

quoted

Sent: 04 October 2020 11:17

With the ioctl interface, when autoneg is enabled, but without
specifying speed, duplex or link modes, the advertised link modes are
set to the supported link modes by the ethtool user space utility.

...

quoted

Fix this incompatibility problem by introducing a new flag in the
ethtool netlink request header: 'ETHTOOL_FLAG_LEGACY'. The purpose of
the flag is to indicate to the kernel that it needs to be compatible
with the legacy ioctl interface. A patch to the ethtool user space
utility will make sure the flag is always set.

You need to do that the other way around.
You can't assume the kernel and application are updated
at the same time.

Thanks, David. In case ethtool is updated without updating the kernel we
will indeed get an error:

# ethtool -s eth0 autoneg on
netlink error: unrecognized request flags (offset 36)
netlink error: Operation not supported

Will wait for Michal's comments before doing another round.

Inverting the logic of the flag wouldn't help much as any tool using the
inverted flag would have the same problem with older kernels. Also,
ethtool needs to handle such errors for any newly added global flag as
discussed in

  http://lkml.kernel.org/r/20200923224510.h3kpgczd6wkpoitp@lion.mk-sys.cz

I'll be too busy today but I'll try to propose a patch implementing the
retry logic in ethtool tomorrow morning.

Michal