On 07/06/13 18:05, Chris Stankevitz wrote:
On Fri, Jun 7, 2013 at 1:06 AM, Alan McKinnon <alan.mckin...@gmail.com> wrote:Regarding this string "eth0":1. What does this string represent? Is it a file on a filesystem? (no!) Is it okay for me to call it an "ethernet *device*"It's just a name.I'm interested in a bit more resolution here. I believe we established that the name "eth0" is given by the kernel. Presumably these names are made available through system calls. What is the name of the system call that provides these monikers? I'm curious by what moniker systemcalls refer to these devices. For example, is the systemcall that retrieves these monikers called "GetEthernetNames"?
http://www.kernel.org/doc/htmldocs/device-drivers/API-device-rename.html and top of this file will tell how the names calculate: http://cgit.freedesktop.org/systemd/systemd/tree/src/udev/udev-builtin-net_id.c#n20
What you CANNOT do with udev is eg switch the names eth0 and eth1 around after the kernel has named them. That was tried for years, it doesn't work. So now udev never interferes with kernel namespace, it create it's own namespaceOkay. From your description I conclude that there are two classes of names for ethernet devices. "Kernel ethernet names" and "udev ethernet names". When a userland utility (wuch as ifconfig) takes an "ethernet device name" as input are they expecting a "kernel ethernet name" or the "udev ethernet name"? That question can be answered with a simple "kernel" or "udev" but I'm interested in a little more
everything will use the same, which is whatever you last used to rename the device as udev is userspace just as much `ip` command from iproute2 package is boot -> kernel assigns eth0 -> the name is now eth0 to userspace -> at this point you rename it to something else, using udev, ip, ipconfig, or whatever and use it everywhere, or don't rename at all and keep using the kernel assigned name
case1:boot using net.ifnames=0 -> kernel assigns eth0 -> udev sees net.ifnames=0 and doesn't rename to anything -> user uses eth0 in whatever he is doing
case2:boot with the default which is net.ifnames=1 -> kernel assigns to eth0 -> udev sees net-ifnames=1 and reads it's rules and renames accordingly to for example enp1s0
detail. What do these userland utilities do with the name? Are these
utilities calling systemcalls such as
GivePropertiesOnEthernetNameInKernelNamespace("eth0")? Are they
establishing a connection to a udev server and querying based on udev
namespace names?
The goal of these questions is not for me to determine if udev is good
or bad, debate global warming, etc. I just want to technically
understand these names, what their differences are, where they come
from, how they are referred in various function calls, etc.
hope above links help explaining in better...
Chris
