On Sat, 4 Aug 2007, Stefan Richter wrote:
[email protected] wrote:
On Fri, 3 Aug 2007, Stefan Richter wrote:
There is a variety of possible naming schemes:
- Naming by order of discovery.
- Naming by vendor/model name strings.
- Naming by universally unique identifier.
- Naming by topology.
- ...
Only the simplest of these schemes (naming by order of discovery)
(which is in most cases also the scheme that's the least useful to
admins and users)
is hardwired into the kernel portion of the Linux OS. The other naming
schemes are (or can be) implemented in the userland portion of the
Linux OS.
...
I understand the flexibility that this provides, unfortunantly (IMHO)
default udev rules (or at least what many distros are shipping by
default) changes from this simple naming scheme in a way that hides the
fact from the user. This means that many users will not even realize the
change in policy until the hardware changes and things don't act the way
they were expected to. In my case it was removing 3 quad cards from a
machine and finding that there was no eth0 on the box, instead there was
a eth12, this is fairly benign. what would have caused me significant
problems would have been having a card fail in a production box, have it
replaced and then found that the interfaces were now eth4-eth22 instead
of eth0-eth18. having the interfaces named differently on different
boxes with identical hardware based on the history of what has been
plugged into the boxes in the past is not what sysadmins expect.
Yes, these rules by far don't fit everyone's needs. People who often
use hotpluggable NICs are probably served best by MAC address based
naming. Boxes with field replacable but otherwise fixed NICs apparently
rather need a naming scheme based on PCI/PCIe topology. (This requires
that the topology is exposed to userspace in comparable manner across
boots and across kernel version updates.)
the detection order works pretty well, we don't do parallel detection yet,
and when we do having parallel detection, but serial registration (in a
defined order) will work.
yes, this can change across kernel version, but in practice it seldom
does. having run linux on production systems since the 2.0 days (and on
personal systems since before 0.99) there have only been a handful of
times when the detection order has changed.
So, an administrator should get to choose between different well
documented naming schemes.
Also, like Jan mentioned, confusion can already be minimized by renaming
eth[0-9]+ -> net_[a-z]+ (for example, or nic[0-9]+ like Jan wrote)
rather than eth[0-9]+ -> eth[0-9]+. That way it's clearer at all times
whether the original names or names given by userspace are used.
And there should be a log message when a device was renamed. Better
yet, like Michal wrote: In case of device files for mass storage, there
is no _renaming_. Instead, udev creates _aliases_ (symlinks), and it
does so with a few different naming schemes at once so that admins or
users immediately have a choice:
$ ls /dev/disk/
by-id by-path by-uuid
Any chance that there could be aliases to network interfaces? Aliases
for device files are easy --- they live only in userspace.
useing different names for the MAC based names, and providing both names
at once would work very well.
David Lang
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