On Tue, Aug 11, 2020 at 09:31:05PM +0200, Lennart Poettering wrote: > On Di, 11.08.20 20:49, Miklos Szeredi (miklos@xxxxxxxxxx) wrote: > > > On Tue, Aug 11, 2020 at 6:05 PM Linus Torvalds > > <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote: > > > > > and then people do "$(srctree)/". If you haven't seen that kind of > > > pattern where the pathname has two (or sometimes more!) slashes in the > > > middle, you've led a very sheltered life. > > > > Oh, I have. That's why I opted for triple slashes, since that should > > work most of the time even in those concatenated cases. And yes, I > > know, most is not always, and this might just be hiding bugs, etc... > > I think the pragmatic approach would be to try this and see how many > > triple slash hits a normal workload gets and if it's reasonably low, > > then hopefully that together with warnings for O_ALT would be enough. > > There's no point. Userspace relies on the current meaning of triple > slashes. It really does. > > I know many places in systemd where we might end up with a triple > slash. Here's a real-life example: some code wants to access the > cgroup attribute 'cgroup.controllers' of the root cgroup. It thus > generates the right path in the fs for it, which is the concatenation of > "/sys/fs/cgroup/" (because that's where cgroupfs is mounted), of "/" > (i.e. for the root cgroup) and of "/cgroup.controllers" (as that's the > file the attribute is exposed under). > > And there you go: > > "/sys/fs/cgroup/" + "/" + "/cgroup.controllers" → "/sys/fs/cgroup///cgroup.controllers" > > This is a real-life thing. Don't break this please. Taken from a log from a container: lxc f4 20200810105815.742 TRACE cgfsng - cgroups/cgfsng.c:cg_legacy_handle_cpuset_hierarchy:552 - "cgroup.clone_children" was already set to "1" lxc f4 20200810105815.742 WARN cgfsng - cgroups/cgfsng.c:mkdir_eexist_on_last:1152 - File exists - Failed to create directory "/sys/fs/cgroup/cpuset///lxc.monitor.f4" lxc f4 20200810105815.743 INFO cgfsng - cgroups/cgfsng.c:cgfsng_monitor_create:1366 - The monitor process uses "lxc.monitor.f4" as cgroup lxc f4 20200810105815.743 DEBUG storage - storage/storage.c:get_storage_by_name:211 - Detected rootfs type "dir" lxc f4 20200810105815.743 TRACE cgfsng - cgroups/cgfsng.c:cg_legacy_handle_cpuset_hierarchy:552 - "cgroup.clone_children" was already set to "1" lxc f4 20200810105815.743 WARN cgfsng - cgroups/cgfsng.c:mkdir_eexist_on_last:1152 - File exists - Failed to create directory "/sys/fs/cgroup/cpuset///lxc.payload.f4" lxc f4 20200810105815.743 INFO cgfsng - cgroups/cgfsng.c:cgfsng_payload_create:1469 - The container process uses "lxc.payload.f4" as cgroup lxc f4 20200810105815.744 TRACE start - start.c:lxc_spawn:1731 - Spawned container directly into target cgroup via cgroup2 fd 17 Christian
