[PATCH net-next v2] ppp: add IFLA_PPP_UNIT netlink attribute

[PATCH net-next v2] ppp: add IFLA_PPP_UNIT netlink attribute

[Martin Olivier]

Currently, the PPP rtnetlink API allows creating a new network interface
with a custom ifname, but it lacks the ability to specify a custom PPP
unit id.

Setting a specific unit id is currently only possible with the
PPPIOCNEWUNIT ioctl. If a user-space program also requires a custom
interface name, it must create the interface first with PPPIOCNEWUNIT
and then rename it.

Resolve this by introducing the IFLA_PPP_UNIT netlink attribute. This
allows user-space programs to atomically request both a custom ifname
and a specific PPP unit id during the RTM_NEWLINK creation process,
eliminating the post-creation renaming for this use case.

Signed-off-by: Martin Olivier <martin.olivier@live.fr>
---
Changes in v2:
- use nl policy to set IFLA_PPP_UNIT min allowed value instead of a manual check in ppp_nl_validate()
- use of nla_get_s32_default() to collect IFLA_PPP_UNIT value
Link to v1: https://lore.kernel.org/netdev/PAWP192MB2411A5E7D3BE1B55E155A92F9747A@PAWP192MB2411.EURP192.PROD.OUTLOOK.COM/
---
 drivers/net/ppp/ppp_generic.c      | 3 ++-
 include/uapi/linux/if_link.h       | 1 +
 tools/include/uapi/linux/if_link.h | 1 +
 3 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ppp/ppp_generic.c b/drivers/net/ppp/ppp_generic.c
index e9b41777be80..3d5d5fe8bad3 100644
--- a/drivers/net/ppp/ppp_generic.c
+++ b/drivers/net/ppp/ppp_generic.c
@@ -1292,6 +1292,7 @@ static int ppp_dev_configure(struct net *src_net, struct net_device *dev,
 
 static const struct nla_policy ppp_nl_policy[IFLA_PPP_MAX + 1] = {
 	[IFLA_PPP_DEV_FD]	= { .type = NLA_S32 },
+	[IFLA_PPP_UNIT]		= NLA_POLICY_MIN(NLA_S32, 0),
 };
 
 static int ppp_nl_validate(struct nlattr *tb[], struct nlattr *data[],
@@ -1316,7 +1317,6 @@ static int ppp_nl_newlink(struct net_device *dev,
 	struct nlattr **data = params->data;
 	struct nlattr **tb = params->tb;
 	struct ppp_config conf = {
-		.unit = -1,
 		.ifname_is_set = true,
 	};
 	struct file *file;
@@ -1342,6 +1342,7 @@ static int ppp_nl_newlink(struct net_device *dev,
 	}
 
 	conf.file = file;
+	conf.unit = nla_get_s32_default(data[IFLA_PPP_UNIT], -1);
 
 	/* Don't use device name generated by the rtnetlink layer when ifname
 	 * isn't specified. Let ppp_dev_configure() set the device name using
diff --git a/include/uapi/linux/if_link.h b/include/uapi/linux/if_link.h
index e9b5f79e1ee1..40523cd01a8b 100644
--- a/include/uapi/linux/if_link.h
+++ b/include/uapi/linux/if_link.h
@@ -1477,6 +1477,7 @@ enum {
 enum {
 	IFLA_PPP_UNSPEC,
 	IFLA_PPP_DEV_FD,
+	IFLA_PPP_UNIT,
 	__IFLA_PPP_MAX
 };
 #define IFLA_PPP_MAX (__IFLA_PPP_MAX - 1)
diff --git a/tools/include/uapi/linux/if_link.h b/tools/include/uapi/linux/if_link.h
index 7e46ca4cd31b..150a582ae498 100644
--- a/tools/include/uapi/linux/if_link.h
+++ b/tools/include/uapi/linux/if_link.h
@@ -1465,6 +1465,7 @@ enum {
 enum {
 	IFLA_PPP_UNSPEC,
 	IFLA_PPP_DEV_FD,
+	IFLA_PPP_UNIT,
 	__IFLA_PPP_MAX
 };
 #define IFLA_PPP_MAX (__IFLA_PPP_MAX - 1)
-- 
2.51.0

Re: [PATCH net-next v2] ppp: add IFLA_PPP_UNIT netlink attribute

[Jakub Kicinski]

On Sat, 14 Mar 2026 02:14:29 +0100 Martin Olivier wrote:
> Currently, the PPP rtnetlink API allows creating a new network interface
> with a custom ifname, but it lacks the ability to specify a custom PPP
> unit id.
> 
> Setting a specific unit id is currently only possible with the
> PPPIOCNEWUNIT ioctl. If a user-space program also requires a custom
> interface name, it must create the interface first with PPPIOCNEWUNIT
> and then rename it.
> 
> Resolve this by introducing the IFLA_PPP_UNIT netlink attribute. This
> allows user-space programs to atomically request both a custom ifname
> and a specific PPP unit id during the RTM_NEWLINK creation process,
> eliminating the post-creation renaming for this use case.

Qingfang Deng, you work on PPP, could you review this patch, please?

Re: [PATCH net-next v2] ppp: add IFLA_PPP_UNIT netlink attribute

[Qingfang Deng]

On Sat, 14 Mar 2026 02:14:29 +0100, Martin Olivier wrote:
> Currently, the PPP rtnetlink API allows creating a new network interface
> with a custom ifname, but it lacks the ability to specify a custom PPP
> unit id.
> 
> Setting a specific unit id is currently only possible with the
> PPPIOCNEWUNIT ioctl. If a user-space program also requires a custom
> interface name, it must create the interface first with PPPIOCNEWUNIT
> and then rename it.
> 
> Resolve this by introducing the IFLA_PPP_UNIT netlink attribute. This
> allows user-space programs to atomically request both a custom ifname
> and a specific PPP unit id during the RTM_NEWLINK creation process,
> eliminating the post-creation renaming for this use case.
> 
> Signed-off-by: Martin Olivier <martin.olivier@live.fr>
> ---
> Changes in v2:
> - use nl policy to set IFLA_PPP_UNIT min allowed value instead of a manual check in ppp_nl_validate()
> - use of nla_get_s32_default() to collect IFLA_PPP_UNIT value
> Link to v1: https://lore.kernel.org/netdev/PAWP192MB2411A5E7D3BE1B55E155A92F9747A@PAWP192MB2411.EURP192.PROD.OUTLOOK.COM/

The patch itself looks good to me, but I would like to check the
userspace changes too. Please create a pull request at
https://github.com/ppp-project/ppp/pulls

+Cc: Paul Mackerras, Guillaume Nault, Pali Rohár

Regards,
Qingfang

Re: [PATCH net-next v2] ppp: add IFLA_PPP_UNIT netlink attribute

[Guillaume Nault]

On Wed, Mar 18, 2026 at 09:59:29AM +0800, Qingfang Deng wrote:
> On Sat, 14 Mar 2026 02:14:29 +0100, Martin Olivier wrote:
> > Currently, the PPP rtnetlink API allows creating a new network interface
> > with a custom ifname, but it lacks the ability to specify a custom PPP
> > unit id.
> > 
> > Setting a specific unit id is currently only possible with the
> > PPPIOCNEWUNIT ioctl. If a user-space program also requires a custom
> > interface name, it must create the interface first with PPPIOCNEWUNIT
> > and then rename it.
> > 
> > Resolve this by introducing the IFLA_PPP_UNIT netlink attribute. This
> > allows user-space programs to atomically request both a custom ifname
> > and a specific PPP unit id during the RTM_NEWLINK creation process,
> > eliminating the post-creation renaming for this use case.
> > 
> > Signed-off-by: Martin Olivier <martin.olivier@live.fr>
> > ---
> > Changes in v2:
> > - use nl policy to set IFLA_PPP_UNIT min allowed value instead of a manual check in ppp_nl_validate()
> > - use of nla_get_s32_default() to collect IFLA_PPP_UNIT value
> > Link to v1: https://lore.kernel.org/netdev/PAWP192MB2411A5E7D3BE1B55E155A92F9747A@PAWP192MB2411.EURP192.PROD.OUTLOOK.COM/
> 
> The patch itself looks good to me, but I would like to check the
> userspace changes too. Please create a pull request at
> https://github.com/ppp-project/ppp/pulls
> 
> +Cc: Paul Mackerras, Guillaume Nault, Pali Rohár

As far as I understand, the original ioctl API allowed setting the unit
id for only one reason: to allow userspace to influence the name of the
ppp device to be created.

The netlink interface on the other hand already allows to set the
device name, without needing to play with the unit id. So what's the
use case for setting the unit id with netlink?

> Regards,
> Qingfang
> 

Re: [PATCH net-next v2] ppp: add IFLA_PPP_UNIT netlink attribute

[Pali Rohár]

On Wednesday 18 March 2026 09:59:29 Qingfang Deng wrote:
> On Sat, 14 Mar 2026 02:14:29 +0100, Martin Olivier wrote:
> > Currently, the PPP rtnetlink API allows creating a new network interface
> > with a custom ifname, but it lacks the ability to specify a custom PPP
> > unit id.
> > 
> > Setting a specific unit id is currently only possible with the
> > PPPIOCNEWUNIT ioctl. If a user-space program also requires a custom
> > interface name, it must create the interface first with PPPIOCNEWUNIT
> > and then rename it.
> > 
> > Resolve this by introducing the IFLA_PPP_UNIT netlink attribute. This
> > allows user-space programs to atomically request both a custom ifname
> > and a specific PPP unit id during the RTM_NEWLINK creation process,
> > eliminating the post-creation renaming for this use case.
> > 
> > Signed-off-by: Martin Olivier <martin.olivier@live.fr>
> > ---
> > Changes in v2:
> > - use nl policy to set IFLA_PPP_UNIT min allowed value instead of a manual check in ppp_nl_validate()
> > - use of nla_get_s32_default() to collect IFLA_PPP_UNIT value
> > Link to v1: https://lore.kernel.org/netdev/PAWP192MB2411A5E7D3BE1B55E155A92F9747A@PAWP192MB2411.EURP192.PROD.OUTLOOK.COM/
> 
> The patch itself looks good to me, but I would like to check the
> userspace changes too. Please create a pull request at
> https://github.com/ppp-project/ppp/pulls
> 
> +Cc: Paul Mackerras, Guillaume Nault, Pali Rohár
> 
> Regards,
> Qingfang

Hello Martin, in past I have sent similar change:
https://lore.kernel.org/linux-ppp/20210807163749.18316-1-pali@kernel.org/T/#u
Look at the discussion, it can be useful to understand why the change
was not accepted.

Re: [PATCH net-next v2] ppp: add IFLA_PPP_UNIT netlink attribute

[Pali Rohár]

Hello, I was not able to send my previous message to Martin. It failed on error:

<martin.olivier@live.fr>: host eur.olc.protection.outlook.com[52.101.68.24]
    said: 550 5.7.1 Unfortunately, messages from [172.105.4.254] weren't sent.
    Please contact your Internet service provider since part of their network
    is on our block list (S3140). You can also refer your provider to
    http://mail.live.com/mail/troubleshooting.aspx#errors. [Name=Protocol
    Filter Agent][AGT=PFA][MxId=11BD098F3639132A]
    [DB3PEPF0000885E.eurprd02.prod.outlook.com 2026-03-18T10:07:44.206Z
    08DE84C79B425097] (in reply to MAIL FROM command)

Can somebody forward my previous email message to Martin and ideally
mention that error?