Re: [RFC PATCH net-next 1/3] ethtool: Add link down reason callback

Currently, drivers can only tell whether the link is up/down through
ETHTOOL_GLINK callback, but no additional information is given in case
of link down.
This patch provides an infrastructure that allows drivers to hint
the user with the reason why the link is down, in order to ease the
debug process.

Reasons are separated to two types, generic and vendor specific.
Drivers can reply with a generic reason using the enums provided in this
patch (and the ones that will be added in the future), which will be
translated to strings by the userspace ethtool.
In case of a vendor specific reason (not suitable for most vendors),
drivers can reply with ETHTOOL_VENDOR_SPECIFIC reason, in this case the
vendor_reason field should be filled with a vendor specific status code
which will be parsed by the vendor specific userspace parser if one is
available.

This kind of information can save system administrators precious time
which will not be wasted trying to understand why the link won't go
up.

For example, when the cable is unplugged:
$ ethtool ethXX
...
Link detected: no (Cable unplugged)

Signed-off-by: Gal Pressman <redacted>
Signed-off-by: Saeed Mahameed <redacted>
---
 include/linux/ethtool.h      |  2 ++
 include/uapi/linux/ethtool.h | 33 +++++++++++++++++++++++++++++++++
 net/core/ethtool.c           | 24 ++++++++++++++++++++++++
 3 files changed, 59 insertions(+)

diff --git a/include/linux/ethtool.h b/include/linux/ethtool.h
index 83cc986..d472047 100644
--- a/include/linux/ethtool.h
+++ b/include/linux/ethtool.h

@@ -374,5 +374,7 @@ struct ethtool_ops {
 				      struct ethtool_link_ksettings *);
 	int	(*set_link_ksettings)(struct net_device *,
 				      const struct ethtool_link_ksettings *);
+	int	(*get_link_down_reason)(struct net_device *,
+					struct ethtool_link_down_reason *);
 };
 #endif /* _LINUX_ETHTOOL_H */

diff --git a/include/uapi/linux/ethtool.h b/include/uapi/linux/ethtool.h
index 7d4a594..8cf9d2c 100644
--- a/include/uapi/linux/ethtool.h
+++ b/include/uapi/linux/ethtool.h

@@ -550,6 +550,13 @@ struct ethtool_pauseparam {
 
 #define ETH_GSTRING_LEN		32
 
+struct ethtool_link_down_reason {
+	__u32	cmd;
+	__u32	reason;
+	__u32	vendor_reason;
+	__u32	reserved[4];
+};