gcplogs: forcibly set HOME on static UNIX binary

Fix #29344

If HOME is not set, the gcplogs logging driver will call os/user.Current() via oauth2/google.
However, in static binary, os/user.Current() leads to segfault due to a glibc issue that won't be fixed
in a short term. (golang/go#13470, https://sourceware.org/bugzilla/show_bug.cgi?id=19341)
So we forcibly set HOME so as to avoid call to os/user/Current().

Signed-off-by: Akihiro Suda <suda.akihiro@lab.ntt.co.jp>

pkg/homedir/homedir_linux.go

@@ -0,0 +1,23 @@
+// +build linux
+
+package homedir
+
+import (
+	"os"
+
+	"github.com/docker/docker/pkg/idtools"
+)
+
+// GetStatic returns the home directory for the current user without calling
+// os/user.Current(). This is useful for static-linked binary on glibc-based
+// system, because a call to os/user.Current() in a static binary leads to
+// segfault due to a glibc issue that won't be fixed in a short term.
+// (#29344, golang/go#13470, https://sourceware.org/bugzilla/show_bug.cgi?id=19341)
+func GetStatic() (string, error) {
+	uid := os.Getuid()
+	usr, err := idtools.LookupUID(uid)
+	if err != nil {
+		return "", err
+	}
+	return usr.Home, nil
+}

pkg/homedir/homedir_others.go

@@ -0,0 +1,13 @@
+// +build !linux
+
+package homedir
+
+import (
+	"errors"
+)
+
+// GetStatic is not needed for non-linux systems.
+// (Precisely, it is needed only for glibc-based linux systems.)
+func GetStatic() (string, error) {
+	return "", errors.New("homedir.GetStatic() is not supported on this system")
+}