When we use cgroup with systemd driver, the cgroup path will be auto removed
by systemd when all processes exited. So we should check cgroup path exists
when we access the cgroup path, for example in `kill/ps`, or else we will
got an error.
Signed-off-by: lifubang <lifubang@acmcoder.com>
This unties the Gordian Knot of using GetPaths in cgroupv2 code.
The problem is, the current code uses GetPaths for three kinds of things:
1. Get all the paths to cgroup v1 controllers to save its state (see
(*linuxContainer).currentState(), (*LinuxFactory).loadState()
methods).
2. Get all the paths to cgroup v1 controllers to have the setns process
enter the proper cgroups in `(*setnsProcess).start()`.
3. Get the path to a specific controller (for example,
`m.GetPaths()["devices"]`).
Now, for cgroup v2 instead of a set of per-controller paths, we have only
one single unified path, and a dedicated function `GetUnifiedPath()` to get it.
This discrepancy between v1 and v2 cgroupManager API leads to the
following problems with the code:
- multiple if/else code blocks that have to treat v1 and v2 separately;
- backward-compatible GetPaths() methods in v2 controllers;
- - repeated writing of the PID into the same cgroup for v2;
Overall, it's hard to write the right code with all this, and the code
that is written is kinda hard to follow.
The solution is to slightly change the API to do the 3 things outlined
above in the same manner for v1 and v2:
1. Use `GetPaths()` for state saving and setns process cgroups entering.
2. Introduce and use Path(subsys string) to obtain a path to a
subsystem. For v2, the argument is ignored and the unified path is
returned.
This commit converts all the controllers to the new API, and modifies
all the users to use it.
Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>
1. Rename the files
- v1.go: cgroupv1 aka legacy;
- v2.go: cgroupv2 aka unified hierarchy;
- unsupported.go: when systemd is not available.
2. Move the code that is common between v1 and v2 to common.go
Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>
