Re: scan_sys_class_net bug in pcap-linux.c

[Guy Harris <guy () alum mit edu>]

On Dec 2, 2012, at 6:54 PM, Paul Sheer <paulsheer () gmail com> wrote:

> > > !strcmp(ent->d_name, "bonding_masters")) continue;
> >
> > No.
> >
> > That wires in a particular name, and when the *next* weird file gets added by some future kernel revision, we won't 
> > handle it, and would end up wiring in another name, lather, rinse, repeat.
> >
> > Instead, it should ignore "." and "..", ignore all *plain files* (rather than directories), and check whether 
> > there's a "subsystem" item underneath the item (just in case there are directories, or symlinks that point to 
> > directories, in there that *don't* correspond to devices, either now or in the future).
>
> Hmmm
>
> i recall on some systems they are symlinks not directories

Symlinks pointing to directories.  Given that we're looking to see whether there's a "subsystem" underneath the entry 
in question, so that the item in /sys/class/net is the next-to-last component of the pathname rather than the last 
component, the lstat() will follow the symlink in question - one of the goals was to make "is it a directory or a 
symlink?" irrelevant, and looking for something underneath it achieves that goal.

> what about if they don't contain "subsystem" in the future?

Well:

        http://kernel.org/doc/Documentation/sysfs-rules.txt

  The properties of a device are:

        ...

    o subsystem (block, tty, pci, ...)
      - simple string, never a path or a link
      - retrieved by reading the "subsystem"-link and using only the
        last element of the target path

so they appear to be claiming that a "device" will have a ""subsystem"-link". 

> or older kernel versions that don't contain "subsystem" (do they?) ?

2.6.0 doesn't appear to.  "ifindex" would probably be a better choice, as

        1) 2.6.0 *does* have it

and

        2) it's more specific to network interfaces.

I've checked in a change to use ifindex instead.

> or future versions that add subsystem to bonding_masters?

They'd have to make it a directory to do that, but ifindex is safer - if it got an ifindex attribute, that'd be because 
it was an interface....
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