Stub out some functionality on non-Linux platforms

[joestringer]

This is a drive-by attempt to improve the compilability of the Cilium codebase
on non-Linux platforms, taking steps in the direction of simplifying the build
and test process for developers on those platforms. There's still some fairly
significant Linux-only dependencies in the BPF and datapath sections of the
code which this PR does not attempt to resolve, but these are some steps
forward.

• mountinfo: Add stubs for non-Linux platforms
• cgroups: Add stubs for non-Linux platforms
• health: Add stubs for non-Linux platforms
• modules: Add stubs for non-Linux platforms

Tested via:

$ GOOS=darwin go build ./pkg/$foo

[tklauser]

Nice 🍏

I've tried to test the affected packages on macOS and this is what I got:

$ for m in mountinfo cgroups health modules ; do echo "== $m"; go test ./pkg/$m; done
== mountinfo
# github.com/cilium/cilium/pkg/mountinfo [github.com/cilium/cilium/pkg/mountinfo.test]
pkg/mountinfo/mountinfo_test.go:608:37: undefined: unix.PROC_SUPER_MAGIC
pkg/mountinfo/mountinfo_test.go:613:36: undefined: FilesystemTypeBPFFS
FAIL	github.com/cilium/cilium/pkg/mountinfo [build failed]
FAIL
== cgroups
?   	github.com/cilium/cilium/pkg/cgroups	[no test files]
== health
no Go files in /Users/tklauser/go/src/github.com/cilium/cilium/pkg/health
== modules
# github.com/cilium/cilium/pkg/modules [github.com/cilium/cilium/pkg/modules.test]
pkg/modules/modules_test.go:157:22: undefined: parseModulesFile
FAIL	github.com/cilium/cilium/pkg/modules [build failed]
FAIL

The test build failure in pkg/modules should be fairly easy to fix by stubbing out parseModulesFile:

diff --git a/pkg/modules/modules_unspecified.go b/pkg/modules/modules_unspecified.go
index 7261040fe9b4..032dd464cc62 100644
--- a/pkg/modules/modules_unspecified.go
+++ b/pkg/modules/modules_unspecified.go
@@ -16,7 +16,10 @@

 package modules

-import "errors"
+import (
+       "errors"
+       "io"
+)

 var ErrNotImplemented = errors.New("not implemented")

@@ -27,3 +30,7 @@ func listModules() ([]string, error) {
 func moduleLoader() string {
        return "unknown-module-loader"
 }
+
+func parseModulesFile(r io.Reader) ([]string, error) {
+       return nil, ErrNotImplemented
+}

The tests themselves will then fail, but fixing them to deal with ErrNotSupported is certainly out of scope for this PR.

The test build failure in pkg/moutinfo requires stubbing out the FS magic numbers:

diff --git a/pkg/mountinfo/mountinfo_linux.go b/pkg/mountinfo/mountinfo_linux.go
index 12a7a42afdee..1d4913f38b6e 100644
--- a/pkg/mountinfo/mountinfo_linux.go
+++ b/pkg/mountinfo/mountinfo_linux.go
@@ -27,6 +27,8 @@ const (
 	// to be used for IsMountFS.
 	FilesystemTypeBPFFS   = unix.BPF_FS_MAGIC
 	FilesystemTypeCgroup2 = unix.CGROUP2_SUPER_MAGIC
+	filesystemTypeProc    = unix.PROC_SUPER_MAGIC
+	filesystemTypeTmpfs   = unix.TMPFS_MAGIC
 )
 
 // IsMountFS returns two boolean values, checking
diff --git a/pkg/mountinfo/mountinfo_privileged_test.go b/pkg/mountinfo/mountinfo_privileged_test.go
index fd3aa362061b..c7000855176e 100644
--- a/pkg/mountinfo/mountinfo_privileged_test.go
+++ b/pkg/mountinfo/mountinfo_privileged_test.go
@@ -36,7 +36,7 @@ func (s *MountInfoPrivilegedTestSuite) TestIsMountFSbyMount(c *C) {
 	c.Assert(err, IsNil)
 	defer os.RemoveAll(tmpDir)
 
-	mounted, matched, err := IsMountFS(unix.TMPFS_MAGIC, tmpDir)
+	mounted, matched, err := IsMountFS(filesystemTypeTmpfs, tmpDir)
 	c.Assert(err, IsNil)
 	c.Assert(mounted, Equals, false)
 	c.Assert(matched, Equals, false)
@@ -46,13 +46,13 @@ func (s *MountInfoPrivilegedTestSuite) TestIsMountFSbyMount(c *C) {
 	defer unix.Unmount(tmpDir, unix.MNT_DETACH)
 
 	// deliberately check with wrong fstype
-	mounted, matched, err = IsMountFS(unix.PROC_SUPER_MAGIC, tmpDir)
+	mounted, matched, err = IsMountFS(filesystemTypeProc, tmpDir)
 	c.Assert(err, IsNil)
 	c.Assert(mounted, Equals, true)
 	c.Assert(matched, Equals, false)
 
 	// now check with proper fstype
-	mounted, matched, err = IsMountFS(unix.TMPFS_MAGIC, tmpDir)
+	mounted, matched, err = IsMountFS(filesystemTypeTmpfs, tmpDir)
 	c.Assert(err, IsNil)
 	c.Assert(mounted, Equals, true)
 	c.Assert(matched, Equals, true)
diff --git a/pkg/mountinfo/mountinfo_test.go b/pkg/mountinfo/mountinfo_test.go
index 416c704e6b5a..5f41698dacdb 100644
--- a/pkg/mountinfo/mountinfo_test.go
+++ b/pkg/mountinfo/mountinfo_test.go
@@ -21,7 +21,6 @@ import (
 	"testing"
 
 	"github.com/cilium/cilium/pkg/checker"
-	"golang.org/x/sys/unix"
 
 	. "gopkg.in/check.v1"
 )
@@ -605,7 +604,7 @@ func (s *MountInfoTestSuite) TestGetMountInfo(c *C) {
 // system and machine to have any predictable mounts, but let's try a couple
 // of very well known paths.
 func (s *MountInfoTestSuite) TestIsMountFS(c *C) {
-	mounted, matched, err := IsMountFS(unix.PROC_SUPER_MAGIC, "/proc")
+	mounted, matched, err := IsMountFS(filesystemTypeProc, "/proc")
 	c.Assert(err, IsNil)
 	c.Assert(mounted, Equals, true)
 	c.Assert(matched, Equals, true)
diff --git a/pkg/mountinfo/mountinfo_unspecified.go b/pkg/mountinfo/mountinfo_unspecified.go
index 13450d7b7a40..0cbcdb08ea79 100644
--- a/pkg/mountinfo/mountinfo_unspecified.go
+++ b/pkg/mountinfo/mountinfo_unspecified.go
@@ -16,7 +16,17 @@
 
 package mountinfo
 
-import "errors"
+import (
+	"errors"
+)
+
+const (
+	// Dummy FilesystemType superblock magic numbers for filesystems,
+	// to be used for IsMountFS.
+	FilesystemTypeBPFFS = 0
+	filesystemTypeProc  = 0
+	filesystemTypeTmpfs = 0
+)
 
 // IsMountFS returns two boolean values, checking
 //  - whether the path is a mount point;

The tests themselves will also fail, but as with pkg/modules fixing them is out of scope here.

If you want I can also push these changes as fixup commits.

[joestringer]

Thanks @tklauser , I indeed don't actually have the platform available so have been relying on go tooling for this so far. I didn't think of compiling the tests as well, I can probably figure out another command to do just that on other platforms as well. I recall there's some trick to it but I'd have to look it up.

I think that when it comes to the privileged tests, we are almost sure to be relying on Linux to perform the test since the elevated privileges are used to perform syscalls that we otherwise wouldn't have the rights for. So another approach for those tests would be to exclude them from !Linux platforms via go build tags.

Beyond that, sure feel free to push changes if you like. Otherwise I'd be happy to pick up these patch hunks, apply them on top and share authorship with you. In that case I'll take a look later on after some ☕.

[tklauser]

Thanks @tklauser , I indeed don't actually have the platform available so have been relying on go tooling for this so far. I didn't think of compiling the tests as well, I can probably figure out another command to do just that on other platforms as well. I recall there's some trick to it but I'd have to look it up.

You can use e.g. GOOS=darwin go test -c ./pkg/$foo to cross-build the tests on any platform - and pass -tags privileged_test where appropriate. This will create a macOS binary ./pkg/$foo/$foo.test.

I think that when it comes to the privileged tests, we are almost sure to be relying on Linux to perform the test since the elevated privileges are used to perform syscalls that we otherwise wouldn't have the rights for. So another approach for those tests would be to exclude them from !Linux platforms via go build tags.

Agree, I think for the privileged tests it would make sense to add linux build tags.

Beyond that, sure feel free to push changes if you like. Otherwise I'd be happy to pick up these patch hunks, apply them on top and share authorship with you. In that case I'll take a look later on after some ☕.

Whatever works best for you. I've your happy applying the patch hunks, I'll let you go ahead so I don't mess with your workflow.

[joestringer]

I finally got that ☕ ;) I applied the suggested hunks from @tklauser, added you as a co-author, and re-ran all of the package tests with GOOS=darwin to double-check.

[joestringer]

Actually, the linter didn't like defining vars for the FS magic vars so I just made the tests run on linux only instead.

[tklauser]

Actually, the linter didn't like defining vars for the FS magic vars so I just made the tests run on linux only instead.

Nice 🚀 as a side effect, the tests now "pass" on GOOS=darwin:

$ go test ./pkg/mountinfo
?   	github.com/cilium/cilium/pkg/mountinfo	[no test files]

[pchaigno]

test-me-please

[joestringer]

Filed #15630 for the failure on test-1.21-4.9 since I see no way that some code tidying like this could cause only the net-next run to fail.

[qmonnet]

Considering the net-next failure as a flake documented in the issue you linked, I'll go ahead and merge this. Thanks!