On 12/06/2021 08:01, Greg KH wrote:
On Fri, Jun 11, 2021 at 03:23:39PM +0000, Jonathan Davies wrote:
When the predictable device naming scheme for NICs is not in use, it is
common for there to be udev rules to rename interfaces to names with
prefix "eth".
Since the timing at which USB NICs are discovered is unpredictable, it
can be interfere with udev's attempt to rename another interface to
"eth0" if a freshly discovered USB interface is initially given the name
"eth0".
Hence it is useful to be able to override the default name. A new usbnet
module parameter allows this to be configured.
Signed-off-by: Jonathan Davies <jonathan.davies@xxxxxxxxxxx>
Suggested-by: Prashanth Sreenivasa <prashanth.sreenivasa@xxxxxxxxxxx>
---
drivers/net/usb/usbnet.c | 13 ++++++++++---
1 file changed, 10 insertions(+), 3 deletions(-)
diff --git a/drivers/net/usb/usbnet.c b/drivers/net/usb/usbnet.c
index ecf6284..55f6230 100644
--- a/drivers/net/usb/usbnet.c
+++ b/drivers/net/usb/usbnet.c
@@ -72,6 +72,13 @@ static int msg_level = -1;
module_param (msg_level, int, 0);
MODULE_PARM_DESC (msg_level, "Override default message level");
+#define DEFAULT_ETH_DEV_NAME "eth%d"
+
+static char *eth_device_name = DEFAULT_ETH_DEV_NAME;
+module_param(eth_device_name, charp, 0644);
+MODULE_PARM_DESC(eth_device_name, "Device name pattern for Ethernet devices"
+ " (default: \"" DEFAULT_ETH_DEV_NAME "\")");
This is not the 1990's, please do not add new module parameters as they
are on a global driver level, and not on a device level.
The initial name is set at probe-time, so the device doesn't exist yet.
So I felt like it was a choice between either changing the hard-coded
"eth%d" string or providing a driver-level module parameter. Is there a
better alternative?
Also changing the way usb network devices are named is up to userspace,
the kernel should not be involved in this. What is wrong with just
renaming it in userspace as you want to today?
Yes, renaming devices is the responsibility of userspace. Normally udev
will rename a device shortly after it is probed. But there's a window
during which it has the name the kernel initially assigns. If there's
other renaming activity happening during that window there's a chance of
collisions.
Userspace solutions include:
1. udev backing off and retrying in the event of a collision; or
2. avoiding ever renaming a device to a name in the "eth%d" namespace.
Solution 1 is ugly and slow. It's much neater to avoid the collisions in
the first place where possible.
Solution 2 arises naturally from use of the predictable device naming
scheme. But when userspace is not using that, solution 2 may not apply.
Yes, the problem is a result of userspace decisions, but that doesn't
mean the kernel can't help make things easier.
Thanks,
Jonathan
