[systemd-devel] [PATCH 2/2] nspawn: skip symlink to a combined cgroup hierarchy if it already exists

[Iago López Galeiras]

If a symlink to a combined cgroup hierarchy already exists and points to
the right path, skip it. This avoids an error when the cgroups are set
manually before calling nspawn.
---
 src/nspawn/nspawn.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/src/nspawn/nspawn.c b/src/nspawn/nspawn.c
index c67cab2..cc0b84f 100644
--- a/src/nspawn/nspawn.c
+++ b/src/nspawn/nspawn.c
@@ -1113,7 +1113,7 @@ static int mount_cgroup(const char *dest) {
                 } else if (r < 0)
                         return log_error_errno(r, "Failed to read link %s: %m", origin);
                 else {
-                        _cleanup_free_ char *target = NULL;
+                        _cleanup_free_ char *target = NULL, *p = NULL;
 
                         target = strjoin(dest, "/sys/fs/cgroup/", controller, NULL);
                         if (!target)
@@ -1130,8 +1130,18 @@ static int mount_cgroup(const char *dest) {
                         if (r < 0)
                                 return r;
 
-                        if (symlink(combined, target) < 0)
+                        if (symlink(combined, target) < 0) {
+                            if (errno == EEXIST) {
+                                r = readlink_malloc(target, &p);
+                                if (r < 0)
+                                    return log_error_errno(r, "Failed to read link %s: %m", target);
+                                else if (!streq(p, combined)) {
+                                    log_error("Invalid existing symlink for combined hierarchy");
+                                    return -EINVAL;
+                                }
+                            } else
                                 return log_error_errno(errno, "Failed to create symlink for combined hierarchy: %m");
+                        }
                 }
         }
 
-- 
2.4.0