[PATCH v3 0/2] netconsole: allow selection of egress interface via MAC address

[PATCH v3 0/2] netconsole: allow selection of egress interface via MAC address

[Uday Shankar]

This series adds support for selecting a netconsole egress interface by
specifying the MAC address (in place of the interface name) in the
boot/module parameter.

Signed-off-by: Uday Shankar <ushankar@purestorage.com>
---
Changes in v3:
- Rename MAC_ADDR_LEN to MAC_ADDR_STR_LEN (Johannes Berg)
- Link to v2: https://lore.kernel.org/r/20250204-netconsole-v2-0-5ef5eb5f6056@purestorage.com

---
Uday Shankar (2):
      net, treewide: define and use MAC_ADDR_STR_LEN
      netconsole: allow selection of egress interface via MAC address

 Documentation/networking/netconsole.rst |  6 +++-
 drivers/net/netconsole.c                |  2 +-
 drivers/nvmem/brcm_nvram.c              |  2 +-
 drivers/nvmem/layouts/u-boot-env.c      |  2 +-
 include/linux/if_ether.h                |  3 ++
 include/linux/netpoll.h                 |  6 ++++
 lib/net_utils.c                         |  4 +--
 net/core/netpoll.c                      | 51 +++++++++++++++++++++++++--------
 net/mac80211/debugfs_sta.c              |  5 ++--
 9 files changed, 60 insertions(+), 21 deletions(-)
---
base-commit: 3924fa995cdf3752f2f89f8de72834c4638c5ebf
change-id: 20250204-netconsole-4c610e2f871c

Best regards,
-- 
Uday Shankar <ushankar@purestorage.com>

[PATCH v3 1/2] net, treewide: define and use MAC_ADDR_STR_LEN

[Uday Shankar]

There are a few places in the tree which compute the length of the
string representation of a MAC address as 3 * ETH_ALEN - 1. Define a
constant for this and use it where relevant. No functionality changes
are expected.

Signed-off-by: Uday Shankar <ushankar@purestorage.com>
---
 drivers/net/netconsole.c           | 2 +-
 drivers/nvmem/brcm_nvram.c         | 2 +-
 drivers/nvmem/layouts/u-boot-env.c | 2 +-
 include/linux/if_ether.h           | 3 +++
 lib/net_utils.c                    | 4 +---
 net/mac80211/debugfs_sta.c         | 5 +++--
 6 files changed, 10 insertions(+), 8 deletions(-)

diff --git a/drivers/net/netconsole.c b/drivers/net/netconsole.c
index 86ab4a42769a49eebe5dd6f01dafafc6c86ec54f..6db5af2d8d059fa5c072194545d4408eec19b4a9 100644
--- a/drivers/net/netconsole.c
+++ b/drivers/net/netconsole.c
@@ -675,7 +675,7 @@ static ssize_t remote_mac_store(struct config_item *item, const char *buf,
 
 	if (!mac_pton(buf, remote_mac))
 		goto out_unlock;
-	if (buf[3 * ETH_ALEN - 1] && buf[3 * ETH_ALEN - 1] != '\n')
+	if (buf[MAC_ADDR_STR_LEN] && buf[MAC_ADDR_STR_LEN] != '\n')
 		goto out_unlock;
 	memcpy(nt->np.remote_mac, remote_mac, ETH_ALEN);
 
diff --git a/drivers/nvmem/brcm_nvram.c b/drivers/nvmem/brcm_nvram.c
index b810df727b446b1762a1851750f743e0de6e8788..b4cf245fb2467d281111001bb7ed8db5993a09b2 100644
--- a/drivers/nvmem/brcm_nvram.c
+++ b/drivers/nvmem/brcm_nvram.c
@@ -100,7 +100,7 @@ static int brcm_nvram_read_post_process_macaddr(void *context, const char *id, i
 {
 	u8 mac[ETH_ALEN];
 
-	if (bytes != 3 * ETH_ALEN - 1)
+	if (bytes != MAC_ADDR_STR_LEN)
 		return -EINVAL;
 
 	if (!mac_pton(buf, mac))
diff --git a/drivers/nvmem/layouts/u-boot-env.c b/drivers/nvmem/layouts/u-boot-env.c
index 731e6f4f12b2bf28e4547d128954a095545ad461..436426d4e8f910b51b92f88acddfbb40d374587a 100644
--- a/drivers/nvmem/layouts/u-boot-env.c
+++ b/drivers/nvmem/layouts/u-boot-env.c
@@ -37,7 +37,7 @@ static int u_boot_env_read_post_process_ethaddr(void *context, const char *id, i
 {
 	u8 mac[ETH_ALEN];
 
-	if (bytes != 3 * ETH_ALEN - 1)
+	if (bytes != MAC_ADDR_STR_LEN)
 		return -EINVAL;
 
 	if (!mac_pton(buf, mac))
diff --git a/include/linux/if_ether.h b/include/linux/if_ether.h
index 8a9792a6427ad9cf58b50c79cbfe185615800dcb..61b7335aa037c7232a0caa45572043057c02dde3 100644
--- a/include/linux/if_ether.h
+++ b/include/linux/if_ether.h
@@ -19,6 +19,9 @@
 #include <linux/skbuff.h>
 #include <uapi/linux/if_ether.h>
 
+/* XX:XX:XX:XX:XX:XX */
+#define MAC_ADDR_STR_LEN (3 * ETH_ALEN - 1)
+
 static inline struct ethhdr *eth_hdr(const struct sk_buff *skb)
 {
 	return (struct ethhdr *)skb_mac_header(skb);
diff --git a/lib/net_utils.c b/lib/net_utils.c
index 42bb0473fb22f977409f7a6792bb1340f4e911c3..215cda672fee1b5a029c2b61529c6813c0edab11 100644
--- a/lib/net_utils.c
+++ b/lib/net_utils.c
@@ -7,11 +7,9 @@
 
 bool mac_pton(const char *s, u8 *mac)
 {
-	size_t maxlen = 3 * ETH_ALEN - 1;
 	int i;
 
-	/* XX:XX:XX:XX:XX:XX */
-	if (strnlen(s, maxlen) < maxlen)
+	if (strnlen(s, MAC_ADDR_STR_LEN) < MAC_ADDR_STR_LEN)
 		return false;
 
 	/* Don't dirty result unless string is valid MAC. */
diff --git a/net/mac80211/debugfs_sta.c b/net/mac80211/debugfs_sta.c
index a67a9d3160086ac492d77092a0c8a74d2384b28c..11d51e348339f1eec1a7d3fd04b1439aaed64593 100644
--- a/net/mac80211/debugfs_sta.c
+++ b/net/mac80211/debugfs_sta.c
@@ -457,11 +457,12 @@ static ssize_t link_sta_addr_read(struct file *file, char __user *userbuf,
 				  size_t count, loff_t *ppos)
 {
 	struct link_sta_info *link_sta = file->private_data;
-	u8 mac[3 * ETH_ALEN + 1];
+	u8 mac[MAC_ADDR_STR_LEN + 2];
 
 	snprintf(mac, sizeof(mac), "%pM\n", link_sta->pub->addr);
 
-	return simple_read_from_buffer(userbuf, count, ppos, mac, 3 * ETH_ALEN);
+	return simple_read_from_buffer(userbuf, count, ppos, mac,
+				       MAC_ADDR_STR_LEN + 1);
 }
 
 LINK_STA_OPS(addr);

-- 
2.34.1

[PATCH v3 2/2] netconsole: allow selection of egress interface via MAC address

[Uday Shankar]

Currently, netconsole has two methods of configuration - module
parameter and configfs. The former interface allows for netconsole
activation earlier during boot (by specifying the module parameter on
the kernel command line), so it is preferred for debugging issues which
arise before userspace is up/the configfs interface can be used. The
module parameter syntax requires specifying the egress interface name.
This requirement makes it hard to use for a couple reasons:
- The egress interface name can be hard or impossible to predict. For
  example, installing a new network card in a system can change the
  interface names assigned by the kernel.
- When constructing the module parameter, one may have trouble
  determining the original (kernel-assigned) name of the interface
  (which is the name that should be given to netconsole) if some stable
  interface naming scheme is in effect. A human can usually look at
  kernel logs to determine the original name, but this is very painful
  if automation is constructing the parameter.

For these reasons, allow selection of the egress interface via MAC
address when configuring netconsole using the module parameter. Update
the netconsole documentation with an example of the new syntax.
Selection of egress interface by MAC address via configfs is far less
interesting (since when this interface can be used, one should be able
to easily convert between MAC address and interface name), so it is left
unimplemented.

Signed-off-by: Uday Shankar <ushankar@purestorage.com>
Reviewed-by: Breno Leitao <leitao@debian.org>
Tested-by: Breno Leitao <leitao@debian.org>
---
 Documentation/networking/netconsole.rst |  6 +++-
 include/linux/netpoll.h                 |  6 ++++
 net/core/netpoll.c                      | 51 +++++++++++++++++++++++++--------
 3 files changed, 50 insertions(+), 13 deletions(-)

diff --git a/Documentation/networking/netconsole.rst b/Documentation/networking/netconsole.rst
index 94c4680fdf3e7e1a0020d11b44547acfd68072a5..90a1bbb52918a0163828f4e96c89781e0bc6856b 100644
--- a/Documentation/networking/netconsole.rst
+++ b/Documentation/networking/netconsole.rst
@@ -45,7 +45,7 @@ following format::
 	r             if present, prepend kernel version (release) to the message
 	src-port      source for UDP packets (defaults to 6665)
 	src-ip        source IP to use (interface address)
-	dev           network interface (eth0)
+	dev           network interface name (eth0) or MAC address
 	tgt-port      port for logging agent (6666)
 	tgt-ip        IP address for logging agent
 	tgt-macaddr   ethernet MAC address for logging agent (broadcast)
@@ -62,6 +62,10 @@ or using IPv6::
 
  insmod netconsole netconsole=@/,@fd00:1:2:3::1/
 
+or using a MAC address to select the egress interface::
+
+   linux netconsole=4444@10.0.0.1/22:33:44:55:66:77,9353@10.0.0.2/12:34:56:78:9a:bc
+
 It also supports logging to multiple remote agents by specifying
 parameters for the multiple agents separated by semicolons and the
 complete string enclosed in "quotes", thusly::
diff --git a/include/linux/netpoll.h b/include/linux/netpoll.h
index f91e50a76efd4b016381c632456397eea1ea877f..1ade65b59be49cfdcf86ed6e938287b949aa9f58 100644
--- a/include/linux/netpoll.h
+++ b/include/linux/netpoll.h
@@ -25,7 +25,13 @@ union inet_addr {
 struct netpoll {
 	struct net_device *dev;
 	netdevice_tracker dev_tracker;
+	/*
+	 * Either dev_name or dev_mac can be used to specify the local
+	 * interface - dev_name is used if it is a nonempty string, else
+	 * dev_mac is used.
+	 */
 	char dev_name[IFNAMSIZ];
+	u8 dev_mac[ETH_ALEN];
 	const char *name;
 
 	union inet_addr local_ip, remote_ip;
diff --git a/net/core/netpoll.c b/net/core/netpoll.c
index 62b4041aae1ae8c7dc47c89fb40b14bbd4ad0e0e..327c409b1974b9ecc1e078c78ca090b05c3ca9dd 100644
--- a/net/core/netpoll.c
+++ b/net/core/netpoll.c
@@ -501,7 +501,8 @@ void netpoll_print_options(struct netpoll *np)
 		np_info(np, "local IPv6 address %pI6c\n", &np->local_ip.in6);
 	else
 		np_info(np, "local IPv4 address %pI4\n", &np->local_ip.ip);
-	np_info(np, "interface '%s'\n", np->dev_name);
+	np_info(np, "interface name '%s'\n", np->dev_name);
+	np_info(np, "local ethernet address '%pM'\n", np->dev_mac);
 	np_info(np, "remote port %d\n", np->remote_port);
 	if (np->ipv6)
 		np_info(np, "remote IPv6 address %pI6c\n", &np->remote_ip.in6);
@@ -570,11 +571,18 @@ int netpoll_parse_options(struct netpoll *np, char *opt)
 	cur++;
 
 	if (*cur != ',') {
-		/* parse out dev name */
+		/* parse out dev_name or dev_mac */
 		if ((delim = strchr(cur, ',')) == NULL)
 			goto parse_failed;
 		*delim = 0;
-		strscpy(np->dev_name, cur, sizeof(np->dev_name));
+
+		np->dev_name[0] = '\0';
+		eth_broadcast_addr(np->dev_mac);
+		if (!strchr(cur, ':'))
+			strscpy(np->dev_name, cur, sizeof(np->dev_name));
+		else if (!mac_pton(cur, np->dev_mac))
+			goto parse_failed;
+
 		cur = delim;
 	}
 	cur++;
@@ -679,27 +687,45 @@ int __netpoll_setup(struct netpoll *np, struct net_device *ndev)
 }
 EXPORT_SYMBOL_GPL(__netpoll_setup);
 
+/*
+ * Returns a pointer to a string representation of the identifier used
+ * to select the egress interface for the given netpoll instance. buf
+ * must be a buffer of length at least MAC_ADDR_STR_LEN + 1.
+ */
+static char *egress_dev(struct netpoll *np, char *buf)
+{
+	if (np->dev_name[0])
+		return np->dev_name;
+
+	snprintf(buf, MAC_ADDR_STR_LEN, "%pM", np->dev_mac);
+	return buf;
+}
+
 int netpoll_setup(struct netpoll *np)
 {
+	struct net *net = current->nsproxy->net_ns;
+	char buf[MAC_ADDR_STR_LEN + 1];
 	struct net_device *ndev = NULL;
 	bool ip_overwritten = false;
 	struct in_device *in_dev;
 	int err;
 
 	rtnl_lock();
-	if (np->dev_name[0]) {
-		struct net *net = current->nsproxy->net_ns;
+	if (np->dev_name[0])
 		ndev = __dev_get_by_name(net, np->dev_name);
-	}
+	else if (is_valid_ether_addr(np->dev_mac))
+		ndev = dev_getbyhwaddr_rcu(net, ARPHRD_ETHER, np->dev_mac);
+
 	if (!ndev) {
-		np_err(np, "%s doesn't exist, aborting\n", np->dev_name);
+		np_err(np, "%s doesn't exist, aborting\n", egress_dev(np, buf));
 		err = -ENODEV;
 		goto unlock;
 	}
 	netdev_hold(ndev, &np->dev_tracker, GFP_KERNEL);
 
 	if (netdev_master_upper_dev_get(ndev)) {
-		np_err(np, "%s is a slave device, aborting\n", np->dev_name);
+		np_err(np, "%s is a slave device, aborting\n",
+		       egress_dev(np, buf));
 		err = -EBUSY;
 		goto put;
 	}
@@ -707,7 +733,8 @@ int netpoll_setup(struct netpoll *np)
 	if (!netif_running(ndev)) {
 		unsigned long atmost;
 
-		np_info(np, "device %s not up yet, forcing it\n", np->dev_name);
+		np_info(np, "device %s not up yet, forcing it\n",
+			egress_dev(np, buf));
 
 		err = dev_open(ndev, NULL);
 
@@ -741,7 +768,7 @@ int netpoll_setup(struct netpoll *np)
 			if (!ifa) {
 put_noaddr:
 				np_err(np, "no IP address for %s, aborting\n",
-				       np->dev_name);
+				       egress_dev(np, buf));
 				err = -EDESTADDRREQ;
 				goto put;
 			}
@@ -772,13 +799,13 @@ int netpoll_setup(struct netpoll *np)
 			}
 			if (err) {
 				np_err(np, "no IPv6 address for %s, aborting\n",
-				       np->dev_name);
+				       egress_dev(np, buf));
 				goto put;
 			} else
 				np_info(np, "local IPv6 %pI6c\n", &np->local_ip.in6);
 #else
 			np_err(np, "IPv6 is not supported %s, aborting\n",
-			       np->dev_name);
+			       egress_dev(np, buf));
 			err = -EINVAL;
 			goto put;
 #endif

-- 
2.34.1

Re: [PATCH v3 1/2] net, treewide: define and use MAC_ADDR_STR_LEN

[Michal Swiatkowski]

On Wed, Feb 05, 2025 at 10:21:30PM -0700, Uday Shankar wrote:
> There are a few places in the tree which compute the length of the
> string representation of a MAC address as 3 * ETH_ALEN - 1. Define a
> constant for this and use it where relevant. No functionality changes
> are expected.
> 
> Signed-off-by: Uday Shankar <ushankar@purestorage.com>
> ---
>  drivers/net/netconsole.c           | 2 +-
>  drivers/nvmem/brcm_nvram.c         | 2 +-
>  drivers/nvmem/layouts/u-boot-env.c | 2 +-
>  include/linux/if_ether.h           | 3 +++
>  lib/net_utils.c                    | 4 +---
>  net/mac80211/debugfs_sta.c         | 5 +++--
>  6 files changed, 10 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/net/netconsole.c b/drivers/net/netconsole.c
> index 86ab4a42769a49eebe5dd6f01dafafc6c86ec54f..6db5af2d8d059fa5c072194545d4408eec19b4a9 100644
> --- a/drivers/net/netconsole.c
> +++ b/drivers/net/netconsole.c
> @@ -675,7 +675,7 @@ static ssize_t remote_mac_store(struct config_item *item, const char *buf,
>  
[...]

What about ieee80211_sta_debugfs_add()? (net/mac80211/debugfs_sta.c)

In gerneal looks fine, thanks:
Reviewed-by: Michal Swiatkowski <michal.swiatkowski@linux.intel.com>

> 
> -- 
> 2.34.1

Re: [PATCH v3 1/2] net, treewide: define and use MAC_ADDR_STR_LEN

[Johannes Berg]

On Thu, 2025-02-06 at 10:44 +0100, Michal Swiatkowski wrote:
> 
> >  net/mac80211/debugfs_sta.c         | 5 +++--
> 
> What about ieee80211_sta_debugfs_add()? (net/mac80211/debugfs_sta.c)

What about it? It's modified accordingly, just needs a bit more +/-1
now.

For that:
Acked-by: Johannes Berg <johannes@sipsolutions.net>

Thanks for the rename, per the robot report that just came in it looks
like that also saved you from some hassle in drivers that have their own
MAC_ADDR_LEN for some reason :)

johannes

Re: [PATCH v3 1/2] net, treewide: define and use MAC_ADDR_STR_LEN

[Michal Swiatkowski]

On Thu, Feb 06, 2025 at 10:50:36AM +0100, Johannes Berg wrote:
> On Thu, 2025-02-06 at 10:44 +0100, Michal Swiatkowski wrote:
> > 
> > >  net/mac80211/debugfs_sta.c         | 5 +++--
> > 
> > What about ieee80211_sta_debugfs_add()? (net/mac80211/debugfs_sta.c)
> 
> What about it? It's modified accordingly, just needs a bit more +/-1
> now.

I meant that it can be done in this patch too. 

> 
> For that:
> Acked-by: Johannes Berg <johannes@sipsolutions.net>
> 
> Thanks for the rename, per the robot report that just came in it looks
> like that also saved you from some hassle in drivers that have their own
> MAC_ADDR_LEN for some reason :)
> 
> johannes

Re: [PATCH v3 1/2] net, treewide: define and use MAC_ADDR_STR_LEN

[Johannes Berg]

On Thu, 2025-02-06 at 11:24 +0100, Michal Swiatkowski wrote:
> On Thu, Feb 06, 2025 at 10:50:36AM +0100, Johannes Berg wrote:
> > On Thu, 2025-02-06 at 10:44 +0100, Michal Swiatkowski wrote:
> > > 
> > > >  net/mac80211/debugfs_sta.c         | 5 +++--
> > > 
> > > What about ieee80211_sta_debugfs_add()? (net/mac80211/debugfs_sta.c)
> > 
> > What about it? It's modified accordingly, just needs a bit more +/-1
> > now.
> 
> I meant that it can be done in this patch too. 

Oh, oops, right. I thought it _was_ done here, because I didn't pay
enough attention to the actual change. Either way is fine to me though.

johannes

Re: [PATCH v3 2/2] netconsole: allow selection of egress interface via MAC address

[Jakub Kicinski]

On Wed, 05 Feb 2025 22:21:31 -0700 Uday Shankar wrote:
> Currently, netconsole has two methods of configuration - module
> parameter and configfs. The former interface allows for netconsole
> activation earlier during boot (by specifying the module parameter on
> the kernel command line), so it is preferred for debugging issues which
> arise before userspace is up/the configfs interface can be used. The
> module parameter syntax requires specifying the egress interface name.
> This requirement makes it hard to use for a couple reasons:
> - The egress interface name can be hard or impossible to predict. For
>   example, installing a new network card in a system can change the
>   interface names assigned by the kernel.
> - When constructing the module parameter, one may have trouble
>   determining the original (kernel-assigned) name of the interface
>   (which is the name that should be given to netconsole) if some stable
>   interface naming scheme is in effect. A human can usually look at
>   kernel logs to determine the original name, but this is very painful
>   if automation is constructing the parameter.
> 
> For these reasons, allow selection of the egress interface via MAC
> address when configuring netconsole using the module parameter. Update
> the netconsole documentation with an example of the new syntax.
> Selection of egress interface by MAC address via configfs is far less
> interesting (since when this interface can be used, one should be able
> to easily convert between MAC address and interface name), so it is left
> unimplemented.

Sounds like dev_getbyhwaddr_rcu() will warn here. Either wrap it 
in  RCU temporarily or combine the series with Breno's patch to 
add a new helper?
-- 
pw-bot: cr