Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx> writes: >> > 4. Once pinned, map knows its pinned path, just use that, I don't see >> > any reasonable use case where you'd want to override path just for >> > unpinning. >> >> Well, unpinning may need to re-construct the pin path. E.g., >> applications that exit after loading and are re-run after unloading, >> such as iproute2, probably want to be able to unpin maps. Unfortunately >> I don't think there is a way to get the pin path(s) of an object from >> the kernel, though, is there? That would be kinda neat for implementing >> something like `ip link set dev eth0 xdp off unpin`. > > Hm... It seems to me that if application exits and another instance > starts, it should generate pin path using the same logic, then check > if map is already pinned. Then based on settings, either reuse or > unpin first. Either way, pin_path needs to be calculated from map > attributes, not "guessed" by application. Yeah, ideally. However, the bpf object file may not be available (it's not for iproute2, for instance). I'm not sure there's really anything we *can* do about that, though, other than have the application guess. Unless we add more state to the kernel. Would it make sense to store the fact that a map was auto-pinned as a flag in the kernel map info? That way, an application could read that flag along with the name and go looking in /sys/fs/bpf. Hmm, but I guess it could do that anyway; so maybe what we need is just a "try to find all pinned maps of this program" function? That could then to something like: - Get the maps IDs and names of all maps attached to that program from the kernel. - Look for each map name in /sys/fs/bpf - If a pinned map with the same name exists, compare the IDs, and unlink if they match I don't suppose it'll be possible to do all that in a race-free manner, but that would go for any use of unlink() unless I'm missing something? -Toke
