cgroups/cgfsng: rework cgroup attach

Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

diff --git a/src/lxc/cgroups/cgfsng.c b/src/lxc/cgroups/cgfsng.c
index 97dd0b3741c681079f0db9152471d25d83ef660d..cdb1e7eb2d6756e1837b9f04fac6735b51051d71 100644 (file)
--- a/src/lxc/cgroups/cgfsng.c
+++ b/src/lxc/cgroups/cgfsng.c
@@ -2176,39 +2176,41 @@ static inline char *build_full_cgpath_from_monitorpath(struct hierarchy *h,
 
 static int cgroup_attach_leaf(int unified_fd, int64_t pid)
 {
-       int idx = 0;
+       int idx = 1;
        int ret;
        char pidstr[INTTYPE_TO_STRLEN(int64_t) + 1];
+       char attach_cgroup[STRLITERALLEN("lxc-1000/cgroup.procs") + 1];
        size_t pidstr_len;
 
+       /* Create leaf cgroup. */
+       ret = mkdirat(unified_fd, "lxc", 0755);
+       if (ret < 0 && errno != EEXIST)
+               return log_error_errno(-1, errno, "Failed to create leaf cgroup \"lxc\"");
+
        pidstr_len = sprintf(pidstr, INT64_FMT, pid);
-       ret = lxc_writeat(unified_fd, "cgroup.procs", pidstr, pidstr_len);
+       ret = lxc_writeat(unified_fd, "lxc/cgroup.procs", pidstr, pidstr_len);
+       if (ret < 0)
+               ret = lxc_writeat(unified_fd, "cgroup.procs", pidstr, pidstr_len);
        if (ret == 0)
                return 0;
+
        /* this is a non-leaf node */
        if (errno != EBUSY)
                return log_error_errno(-1, errno, "Failed to attach to unified cgroup");
 
        do {
                char *slash;
-               char attach_cgroup[STRLITERALLEN("lxc-1000/cgroup.procs") + 1];
-
-               if (idx)
-                       ret = snprintf(attach_cgroup, sizeof(attach_cgroup),
-                                      "lxc-%d/cgroup.procs", idx);
-               else
-                       ret = snprintf(attach_cgroup, sizeof(attach_cgroup),
-                                      "lxc/cgroup.procs");
-               if (ret < 0 || (size_t)ret >= sizeof(attach_cgroup))
-                       return -1;
 
+               sprintf(attach_cgroup, "lxc-%d/cgroup.procs", idx);
                slash = &attach_cgroup[ret] - STRLITERALLEN("/cgroup.procs");
                *slash = '\0';
+
                ret = mkdirat(unified_fd, attach_cgroup, 0755);
                if (ret < 0 && errno != EEXIST)
                        return log_error_errno(-1, errno, "Failed to create cgroup %s", attach_cgroup);
 
                *slash = '/';
+
                ret = lxc_writeat(unified_fd, attach_cgroup, pidstr, pidstr_len);
                if (ret == 0)
                        return 0;
@@ -2220,7 +2222,7 @@ static int cgroup_attach_leaf(int unified_fd, int64_t pid)
                idx++;
        } while (idx < 1000);
 
-       return -1;
+       return log_error_errno(-1, errno, "Failed to attach to unified cgroup");
 }
 
 int cgroup_attach(const char *name, const char *lxcpath, int64_t pid)