Hi, Not a good answer, just some thoughts:
On Tue, Apr 24, 2018 at 05:51:40PM +0300, Oleg Goldshmidt wrote: > > Hi all, > > I am trying to get my head around the problem of bringing network > interfaces up and down and checking the state. I googled extensively, > but I have not found an answer to the conundrum, and I am hoping that > someone here may shed some light. > > My target platform is Debian wheezy (no, I can't upgrade it), but what I > describe below is very similar on an up-to-date Fedora 27 (that, > obviously, has a very different set of userspace tools and a very > different kernel). > > What I am trying to achieve is as follows. Assume that the system in > question gets a command (imagine an API of sorts) to reconfigure one of > its multiple interfaces. Let's say that the control interface is eth0 > and the request is to reconfigure eth3. Here, "reconfigure" may mean, > e.g., "change the static IP address and maybe some routing rules" (or > toggle between static and DHCP or whatever - staying static seems > conceptually simpler). > > So the is an implementation (bash, run as root, etc.) that goes, in > essence, > > * stop interface eth3 > * change eth3 configuration > * start interface eth3 > > which looks natural enough. It is also natural that there are stop() and > start() functions that may include some subtleties such as flushing IP > address, etc. The start() and stop() functions are used in other > workflows and, in general, one would like to check whether the interface > is up or down, at least to avoid superfluous error messages when one > tries to bring up an interface that is already up, etc. (Such messages > may pollute things for the API client, and hiding stderr in general is > not a good idea because real errors may be lost.) > > The problem is that whatever I do in stop() (or by hand), e.g., > > * ifconfig eth3 down > * ifdown --force eth3 (and --no-scripts, and whatever - on Debian) > * ip link set eth3 down Why don't you stop the interface with 'ifdown'? Also: why not use ip (and generally: iproute2 tools) everywhere? > > etc., etc., with infinite variations, the UP flag remains set (I also > check with ifconfig, ip link show, etc.). > > Technically, the UP flag is the IFF_UP bit in the ifr_flags field of > struct ifreq accessible through a ioctl (cf. man 7 netdevice). I went as > far as writing a C program that uses the ioctl(s) (SIOCGIFFLAGS, > SIOCSIFFLAGS) directly. To no avail: right after I toggle IFF_UP I check > it again and it is *always* up... Again, this is on both Debian wheezy > (old, kernel 3.2.0) and Fedora 27 (fully updated, kernel 4.15.17)... > > It also does not depend on whether the interface is designated as "auto" > (on Debian) or anything else I could think of. "auto" only means this interface is to be started at boot. So it indeed should be irrelevant. -- Tzafrir Cohen | tzaf...@jabber.org | VIM is http://tzafrir.org.il | | a Mutt's tzaf...@cohens.org.il | | best tzaf...@debian.org | | friend _______________________________________________ Linux-il mailing list Linux-il@cs.huji.ac.il http://mailman.cs.huji.ac.il/mailman/listinfo/linux-il
