Add runc_nocr build tag

This allows to make a 17% smaller runc binary by not compiling in
checkpoint/restore support.

It turns out that google.golang.org/protobuf package, used by go-criu,
is quite big, and go linker can't drop unused stuff if reflection is
used anywhere in the code.

Currently there's no alternative to using protobuf in go-criu, and since
not all users use c/r, let's provide them an option for a smaller
binary.

For the reference, here's top10 biggest vendored packages, as reported
by gsa[1]:

$ gsa runc | grep vendor | head
│ 8.59%   │ google.golang.org/protobuf                  │ 1.3 MB │ vendor    │
│ 5.76%   │ github.com/opencontainers/runc              │ 865 kB │ vendor    │
│ 4.05%   │ github.com/cilium/ebpf                      │ 608 kB │ vendor    │
│ 2.86%   │ github.com/godbus/dbus/v5                   │ 429 kB │ vendor    │
│ 1.25%   │ github.com/urfave/cli                       │ 188 kB │ vendor    │
│ 0.90%   │ github.com/vishvananda/netlink              │ 135 kB │ vendor    │
│ 0.59%   │ github.com/sirupsen/logrus                  │ 89 kB  │ vendor    │
│ 0.56%   │ github.com/checkpoint-restore/go-criu/v6    │ 84 kB  │ vendor    │
│ 0.51%   │ golang.org/x/sys                            │ 76 kB  │ vendor    │
│ 0.47%   │ github.com/seccomp/libseccomp-golang        │ 71 kB  │ vendor    │

And here is a total binary size saving when `runc_nocr` is used.

For non-stripped binaries:

$ gsa runc-cr runc-nocr | tail -3
│ -17.04% │ runc-cr                                  │ 15 MB    │ 12 MB    │ -2.6 MB │
│         │ runc-nocr                                │          │          │         │
└─────────┴──────────────────────────────────────────┴──────────┴──────────┴─────────┘

And for stripped binaries:

│ -17.01% │ runc-cr-stripped                         │ 11 MB    │ 8.8 MB   │ -1.8 MB │
│         │ runc-nocr-stripped                       │          │          │         │
└─────────┴──────────────────────────────────────────┴──────────┴──────────┴─────────┘

[1]: https://github.com/Zxilly/go-size-analyzer

Signed-off-by: Kir Kolyshkin <[email protected]>

.github/workflows/validate.yml

@@ -76,8 +76,14 @@ jobs:
         uses: actions/setup-go@v5
         with:
           go-version: "${{ env.GO_VERSION }}"
+      - name: install deps
+        run: |
+          sudo apt update
+          sudo apt -y install libseccomp-dev
       - name: compile with no build tags
         run: make BUILDTAGS=""
+      - name: compile with runc_nocr build tag
+        run: make EXTRA_BUILDTAGS="runc_nocr"
 
   codespell:
     runs-on: ubuntu-24.04

README.md

@@ -103,9 +103,17 @@ e.g. to disable seccomp:
 make BUILDTAGS=""
 ```
 
+To add some more build tags to the default set, use the `EXTRA_BUILDTAGS`
+make variable, e.g. to disable checkpoint/restore:
+
+```bash
+make EXTRA_BUILDTAGS="runc_nocr"
+```
+
 | Build Tag     | Feature                               | Enabled by Default | Dependencies        |
 |---------------|---------------------------------------|--------------------|---------------------|
 | `seccomp`     | Syscall filtering using `libseccomp`. | yes                | `libseccomp`        |
+| `runc_nocr`   | Disables runc checkpoint/restore.     | no                 | `criu`              |
 
 The following build tags were used earlier, but are now obsoleted:
  - **runc_nodmz** (since runc v1.2.1 runc dmz binary is dropped)

libcontainer/criu_linux.go

@@ -1,3 +1,5 @@
+//go:build !runc_nocr
+
 package libcontainer
 
 import (