Adding upstream version 247.3.upstream/247.3upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 841 insertions, 0 deletions

diff --git a/src/shared/cgroup-setup.c b/src/shared/cgroup-setup.c
new file mode 100644
index 0000000..f197f71
--- /dev/null
+++ b/src/shared/cgroup-setup.c
@@ -0,0 +1,841 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+
+#include <ftw.h>
+#include <unistd.h>
+
+#include "cgroup-setup.h"
+#include "cgroup-util.h"
+#include "errno-util.h"
+#include "parse-util.h"
+#include "path-util.h"
+#include "proc-cmdline.h"
+#include "stdio-util.h"
+#include "string-util.h"
+#include "fs-util.h"
+#include "mkdir.h"
+#include "process-util.h"
+#include "fileio.h"
+#include "user-util.h"
+#include "fd-util.h"
+
+bool cg_is_unified_wanted(void) {
+        static thread_local int wanted = -1;
+        bool b;
+        const bool is_default = DEFAULT_HIERARCHY == CGROUP_UNIFIED_ALL;
+        _cleanup_free_ char *c = NULL;
+        int r;
+
+        /* If we have a cached value, return that. */
+        if (wanted >= 0)
+                return wanted;
+
+        /* If the hierarchy is already mounted, then follow whatever was chosen for it. */
+        r = cg_unified_cached(true);
+        if (r >= 0)
+                return (wanted = r >= CGROUP_UNIFIED_ALL);
+
+        /* If we were explicitly passed systemd.unified_cgroup_hierarchy, respect that. */
+        r = proc_cmdline_get_bool("systemd.unified_cgroup_hierarchy", &b);
+        if (r > 0)
+                return (wanted = b);
+
+        /* If we passed cgroup_no_v1=all with no other instructions, it seems highly unlikely that we want to
+         * use hybrid or legacy hierarchy. */
+        r = proc_cmdline_get_key("cgroup_no_v1", 0, &c);
+        if (r > 0 && streq_ptr(c, "all"))
+                return (wanted = true);
+
+        return (wanted = is_default);
+}
+
+bool cg_is_legacy_wanted(void) {
+        static thread_local int wanted = -1;
+
+        /* If we have a cached value, return that. */
+        if (wanted >= 0)
+                return wanted;
+
+        /* Check if we have cgroup v2 already mounted. */
+        if (cg_unified_cached(true) == CGROUP_UNIFIED_ALL)
+                return (wanted = false);
+
+        /* Otherwise, assume that at least partial legacy is wanted,
+         * since cgroup v2 should already be mounted at this point. */
+        return (wanted = true);
+}
+
+bool cg_is_hybrid_wanted(void) {
+        static thread_local int wanted = -1;
+        int r;
+        bool b;
+        const bool is_default = DEFAULT_HIERARCHY >= CGROUP_UNIFIED_SYSTEMD;
+        /* We default to true if the default is "hybrid", obviously, but also when the default is "unified",
+         * because if we get called, it means that unified hierarchy was not mounted. */
+
+        /* If we have a cached value, return that. */
+        if (wanted >= 0)
+                return wanted;
+
+        /* If the hierarchy is already mounted, then follow whatever was chosen for it. */
+        if (cg_unified_cached(true) == CGROUP_UNIFIED_ALL)
+                return (wanted = false);
+
+        /* Otherwise, let's see what the kernel command line has to say.  Since checking is expensive, cache
+         * a non-error result. */
+        r = proc_cmdline_get_bool("systemd.legacy_systemd_cgroup_controller", &b);
+
+        /* The meaning of the kernel option is reversed wrt. to the return value of this function, hence the
+         * negation. */
+        return (wanted = r > 0 ? !b : is_default);
+}
+
+int cg_weight_parse(const char *s, uint64_t *ret) {
+        uint64_t u;
+        int r;
+
+        if (isempty(s)) {
+                *ret = CGROUP_WEIGHT_INVALID;
+                return 0;
+        }
+
+        r = safe_atou64(s, &u);
+        if (r < 0)
+                return r;
+
+        if (u < CGROUP_WEIGHT_MIN || u > CGROUP_WEIGHT_MAX)
+                return -ERANGE;
+
+        *ret = u;
+        return 0;
+}
+
+int cg_cpu_shares_parse(const char *s, uint64_t *ret) {
+        uint64_t u;
+        int r;
+
+        if (isempty(s)) {
+                *ret = CGROUP_CPU_SHARES_INVALID;
+                return 0;
+        }
+
+        r = safe_atou64(s, &u);
+        if (r < 0)
+                return r;
+
+        if (u < CGROUP_CPU_SHARES_MIN || u > CGROUP_CPU_SHARES_MAX)
+                return -ERANGE;
+
+        *ret = u;
+        return 0;
+}
+
+int cg_blkio_weight_parse(const char *s, uint64_t *ret) {
+        uint64_t u;
+        int r;
+
+        if (isempty(s)) {
+                *ret = CGROUP_BLKIO_WEIGHT_INVALID;
+                return 0;
+        }
+
+        r = safe_atou64(s, &u);
+        if (r < 0)
+                return r;
+
+        if (u < CGROUP_BLKIO_WEIGHT_MIN || u > CGROUP_BLKIO_WEIGHT_MAX)
+                return -ERANGE;
+
+        *ret = u;
+        return 0;
+}
+
+static int trim_cb(const char *path, const struct stat *sb, int typeflag, struct FTW *ftwbuf) {
+        assert(path);
+        assert(sb);
+        assert(ftwbuf);
+
+        if (typeflag != FTW_DP)
+                return 0;
+
+        if (ftwbuf->level < 1)
+                return 0;
+
+        (void) rmdir(path);
+        return 0;
+}
+
+int cg_trim(const char *controller, const char *path, bool delete_root) {
+        _cleanup_free_ char *fs = NULL;
+        int r, q;
+
+        assert(path);
+
+        r = cg_get_path(controller, path, NULL, &fs);
+        if (r < 0)
+                return r;
+
+        errno = 0;
+        if (nftw(fs, trim_cb, 64, FTW_DEPTH|FTW_MOUNT|FTW_PHYS) != 0) {
+                if (errno == ENOENT)
+                        r = 0;
+                else
+                        r = errno_or_else(EIO);
+        }
+
+        if (delete_root) {
+                if (rmdir(fs) < 0 && errno != ENOENT)
+                        return -errno;
+        }
+
+        q = cg_hybrid_unified();
+        if (q < 0)
+                return q;
+        if (q > 0 && streq(controller, SYSTEMD_CGROUP_CONTROLLER)) {
+                q = cg_trim(SYSTEMD_CGROUP_CONTROLLER_LEGACY, path, delete_root);
+                if (q < 0)
+                        log_warning_errno(q, "Failed to trim compat systemd cgroup %s: %m", path);
+        }
+
+        return r;
+}
+
+/* Create a cgroup in the hierarchy of controller.
+ * Returns 0 if the group already existed, 1 on success, negative otherwise.
+ */
+int cg_create(const char *controller, const char *path) {
+        _cleanup_free_ char *fs = NULL;
+        int r;
+
+        r = cg_get_path_and_check(controller, path, NULL, &fs);
+        if (r < 0)
+                return r;
+
+        r = mkdir_parents(fs, 0755);
+        if (r < 0)
+                return r;
+
+        r = mkdir_errno_wrapper(fs, 0755);
+        if (r == -EEXIST)
+                return 0;
+        if (r < 0)
+                return r;
+
+        r = cg_hybrid_unified();
+        if (r < 0)
+                return r;
+
+        if (r > 0 && streq(controller, SYSTEMD_CGROUP_CONTROLLER)) {
+                r = cg_create(SYSTEMD_CGROUP_CONTROLLER_LEGACY, path);
+                if (r < 0)
+                        log_warning_errno(r, "Failed to create compat systemd cgroup %s: %m", path);
+        }
+
+        return 1;
+}
+
+int cg_create_and_attach(const char *controller, const char *path, pid_t pid) {
+        int r, q;
+
+        assert(pid >= 0);
+
+        r = cg_create(controller, path);
+        if (r < 0)
+                return r;
+
+        q = cg_attach(controller, path, pid);
+        if (q < 0)
+                return q;
+
+        /* This does not remove the cgroup on failure */
+        return r;
+}
+
+int cg_attach(const char *controller, const char *path, pid_t pid) {
+        _cleanup_free_ char *fs = NULL;
+        char c[DECIMAL_STR_MAX(pid_t) + 2];
+        int r;
+
+        assert(path);
+        assert(pid >= 0);
+
+        r = cg_get_path_and_check(controller, path, "cgroup.procs", &fs);
+        if (r < 0)
+                return r;
+
+        if (pid == 0)
+                pid = getpid_cached();
+
+        xsprintf(c, PID_FMT "\n", pid);
+
+        r = write_string_file(fs, c, WRITE_STRING_FILE_DISABLE_BUFFER);
+        if (r < 0)
+                return r;
+
+        r = cg_hybrid_unified();
+        if (r < 0)
+                return r;
+
+        if (r > 0 && streq(controller, SYSTEMD_CGROUP_CONTROLLER)) {
+                r = cg_attach(SYSTEMD_CGROUP_CONTROLLER_LEGACY, path, pid);
+                if (r < 0)
+                        log_warning_errno(r, "Failed to attach "PID_FMT" to compat systemd cgroup %s: %m", pid, path);
+        }
+
+        return 0;
+}
+
+int cg_attach_fallback(const char *controller, const char *path, pid_t pid) {
+        int r;
+
+        assert(controller);
+        assert(path);
+        assert(pid >= 0);
+
+        r = cg_attach(controller, path, pid);
+        if (r < 0) {
+                char prefix[strlen(path) + 1];
+
+                /* This didn't work? Then let's try all prefixes of
+                 * the destination */
+
+                PATH_FOREACH_PREFIX(prefix, path) {
+                        int q;
+
+                        q = cg_attach(controller, prefix, pid);
+                        if (q >= 0)
+                                return q;
+                }
+        }
+
+        return r;
+}
+
+int cg_set_access(
+                const char *controller,
+                const char *path,
+                uid_t uid,
+                gid_t gid) {
+
+        struct Attribute {
+                const char *name;
+                bool fatal;
+        };
+
+        /* cgroup v1, aka legacy/non-unified */
+        static const struct Attribute legacy_attributes[] = {
+                { "cgroup.procs",           true  },
+                { "tasks",                  false },
+                { "cgroup.clone_children",  false },
+                {},
+        };
+
+        /* cgroup v2, aka unified */
+        static const struct Attribute unified_attributes[] = {
+                { "cgroup.procs",           true  },
+                { "cgroup.subtree_control", true  },
+                { "cgroup.threads",         false },
+                {},
+        };
+
+        static const struct Attribute* const attributes[] = {
+                [false] = legacy_attributes,
+                [true]  = unified_attributes,
+        };
+
+        _cleanup_free_ char *fs = NULL;
+        const struct Attribute *i;
+        int r, unified;
+
+        assert(path);
+
+        if (uid == UID_INVALID && gid == GID_INVALID)
+                return 0;
+
+        unified = cg_unified_controller(controller);
+        if (unified < 0)
+                return unified;
+
+        /* Configure access to the cgroup itself */
+        r = cg_get_path(controller, path, NULL, &fs);
+        if (r < 0)
+                return r;
+
+        r = chmod_and_chown(fs, 0755, uid, gid);
+        if (r < 0)
+                return r;
+
+        /* Configure access to the cgroup's attributes */
+        for (i = attributes[unified]; i->name; i++) {
+                fs = mfree(fs);
+
+                r = cg_get_path(controller, path, i->name, &fs);
+                if (r < 0)
+                        return r;
+
+                r = chmod_and_chown(fs, 0644, uid, gid);
+                if (r < 0) {
+                        if (i->fatal)
+                                return r;
+
+                        log_debug_errno(r, "Failed to set access on cgroup %s, ignoring: %m", fs);
+                }
+        }
+
+        if (streq(controller, SYSTEMD_CGROUP_CONTROLLER)) {
+                r = cg_hybrid_unified();
+                if (r < 0)
+                        return r;
+                if (r > 0) {
+                        /* Always propagate access mode from unified to legacy controller */
+                        r = cg_set_access(SYSTEMD_CGROUP_CONTROLLER_LEGACY, path, uid, gid);
+                        if (r < 0)
+                                log_debug_errno(r, "Failed to set access on compatibility systemd cgroup %s, ignoring: %m", path);
+                }
+        }
+
+        return 0;
+}
+
+int cg_migrate(
+                const char *cfrom,
+                const char *pfrom,
+                const char *cto,
+                const char *pto,
+                CGroupFlags flags) {
+
+        bool done = false;
+        _cleanup_set_free_ Set *s = NULL;
+        int r, ret = 0;
+        pid_t my_pid;
+
+        assert(cfrom);
+        assert(pfrom);
+        assert(cto);
+        assert(pto);
+
+        s = set_new(NULL);
+        if (!s)
+                return -ENOMEM;
+
+        my_pid = getpid_cached();
+
+        do {
+                _cleanup_fclose_ FILE *f = NULL;
+                pid_t pid = 0;
+                done = true;
+
+                r = cg_enumerate_processes(cfrom, pfrom, &f);
+                if (r < 0) {
+                        if (ret >= 0 && r != -ENOENT)
+                                return r;
+
+                        return ret;
+                }
+
+                while ((r = cg_read_pid(f, &pid)) > 0) {
+
+                        /* This might do weird stuff if we aren't a
+                         * single-threaded program. However, we
+                         * luckily know we are not */
+                        if ((flags & CGROUP_IGNORE_SELF) && pid == my_pid)
+                                continue;
+
+                        if (set_get(s, PID_TO_PTR(pid)) == PID_TO_PTR(pid))
+                                continue;
+
+                        /* Ignore kernel threads. Since they can only
+                         * exist in the root cgroup, we only check for
+                         * them there. */
+                        if (cfrom &&
+                            empty_or_root(pfrom) &&
+                            is_kernel_thread(pid) > 0)
+                                continue;
+
+                        r = cg_attach(cto, pto, pid);
+                        if (r < 0) {
+                                if (ret >= 0 && r != -ESRCH)
+                                        ret = r;
+                        } else if (ret == 0)
+                                ret = 1;
+
+                        done = false;
+
+                        r = set_put(s, PID_TO_PTR(pid));
+                        if (r < 0) {
+                                if (ret >= 0)
+                                        return r;
+
+                                return ret;
+                        }
+                }
+
+                if (r < 0) {
+                        if (ret >= 0)
+                                return r;
+
+                        return ret;
+                }
+        } while (!done);
+
+        return ret;
+}
+
+int cg_migrate_recursive(
+                const char *cfrom,
+                const char *pfrom,
+                const char *cto,
+                const char *pto,
+                CGroupFlags flags) {
+
+        _cleanup_closedir_ DIR *d = NULL;
+        int r, ret = 0;
+        char *fn;
+
+        assert(cfrom);
+        assert(pfrom);
+        assert(cto);
+        assert(pto);
+
+        ret = cg_migrate(cfrom, pfrom, cto, pto, flags);
+
+        r = cg_enumerate_subgroups(cfrom, pfrom, &d);
+        if (r < 0) {
+                if (ret >= 0 && r != -ENOENT)
+                        return r;
+
+                return ret;
+        }
+
+        while ((r = cg_read_subgroup(d, &fn)) > 0) {
+                _cleanup_free_ char *p = NULL;
+
+                p = path_join(empty_to_root(pfrom), fn);
+                free(fn);
+                if (!p)
+                        return -ENOMEM;
+
+                r = cg_migrate_recursive(cfrom, p, cto, pto, flags);
+                if (r != 0 && ret >= 0)
+                        ret = r;
+        }
+
+        if (r < 0 && ret >= 0)
+                ret = r;
+
+        if (flags & CGROUP_REMOVE) {
+                r = cg_rmdir(cfrom, pfrom);
+                if (r < 0 && ret >= 0 && !IN_SET(r, -ENOENT, -EBUSY))
+                        return r;
+        }
+
+        return ret;
+}
+
+int cg_migrate_recursive_fallback(
+                const char *cfrom,
+                const char *pfrom,
+                const char *cto,
+                const char *pto,
+                CGroupFlags flags) {
+
+        int r;
+
+        assert(cfrom);
+        assert(pfrom);
+        assert(cto);
+        assert(pto);
+
+        r = cg_migrate_recursive(cfrom, pfrom, cto, pto, flags);
+        if (r < 0) {
+                char prefix[strlen(pto) + 1];
+
+                /* This didn't work? Then let's try all prefixes of the destination */
+
+                PATH_FOREACH_PREFIX(prefix, pto) {
+                        int q;
+
+                        q = cg_migrate_recursive(cfrom, pfrom, cto, prefix, flags);
+                        if (q >= 0)
+                                return q;
+                }
+        }
+
+        return r;
+}
+
+int cg_create_everywhere(CGroupMask supported, CGroupMask mask, const char *path) {
+        CGroupController c;
+        CGroupMask done;
+        bool created;
+        int r;
+
+        /* This one will create a cgroup in our private tree, but also
+         * duplicate it in the trees specified in mask, and remove it
+         * in all others.
+         *
+         * Returns 0 if the group already existed in the systemd hierarchy,
+         * 1 on success, negative otherwise.
+         */
+
+        /* First create the cgroup in our own hierarchy. */
+        r = cg_create(SYSTEMD_CGROUP_CONTROLLER, path);
+        if (r < 0)
+                return r;
+        created = r;
+
+        /* If we are in the unified hierarchy, we are done now */
+        r = cg_all_unified();
+        if (r < 0)
+                return r;
+        if (r > 0)
+                return created;
+
+        supported &= CGROUP_MASK_V1;
+        mask = CGROUP_MASK_EXTEND_JOINED(mask);
+        done = 0;
+
+        /* Otherwise, do the same in the other hierarchies */
+        for (c = 0; c < _CGROUP_CONTROLLER_MAX; c++) {
+                CGroupMask bit = CGROUP_CONTROLLER_TO_MASK(c);
+                const char *n;
+
+                if (!FLAGS_SET(supported, bit))
+                        continue;
+
+                if (FLAGS_SET(done, bit))
+                        continue;
+
+                n = cgroup_controller_to_string(c);
+                if (FLAGS_SET(mask, bit))
+                        (void) cg_create(n, path);
+
+                done |= CGROUP_MASK_EXTEND_JOINED(bit);
+        }
+
+        return created;
+}
+
+int cg_attach_everywhere(CGroupMask supported, const char *path, pid_t pid, cg_migrate_callback_t path_callback, void *userdata) {
+        int r;
+
+        r = cg_attach(SYSTEMD_CGROUP_CONTROLLER, path, pid);
+        if (r < 0)
+                return r;
+
+        r = cg_all_unified();
+        if (r < 0)
+                return r;
+        if (r > 0)
+                return 0;
+
+        supported &= CGROUP_MASK_V1;
+        CGroupMask done = 0;
+
+        for (CGroupController c = 0; c < _CGROUP_CONTROLLER_MAX; c++) {
+                CGroupMask bit = CGROUP_CONTROLLER_TO_MASK(c);
+                const char *p = NULL;
+
+                if (!FLAGS_SET(supported, bit))
+                        continue;
+
+                if (FLAGS_SET(done, bit))
+                        continue;
+
+                if (path_callback)
+                        p = path_callback(bit, userdata);
+                if (!p)
+                        p = path;
+
+                (void) cg_attach_fallback(cgroup_controller_to_string(c), p, pid);
+                done |= CGROUP_MASK_EXTEND_JOINED(bit);
+        }
+
+        return 0;
+}
+
+int cg_migrate_v1_controllers(CGroupMask supported, CGroupMask mask, const char *from, cg_migrate_callback_t to_callback, void *userdata) {
+        CGroupController c;
+        CGroupMask done;
+        int r = 0, q;
+
+        assert(to_callback);
+
+        supported &= CGROUP_MASK_V1;
+        mask = CGROUP_MASK_EXTEND_JOINED(mask);
+        done = 0;
+
+        for (c = 0; c < _CGROUP_CONTROLLER_MAX; c++) {
+                CGroupMask bit = CGROUP_CONTROLLER_TO_MASK(c);
+                const char *to = NULL;
+
+                if (!FLAGS_SET(supported, bit))
+                        continue;
+
+                if (FLAGS_SET(done, bit))
+                        continue;
+
+                if (!FLAGS_SET(mask, bit))
+                        continue;
+
+                to = to_callback(bit, userdata);
+
+                /* Remember first error and try continuing */
+                q = cg_migrate_recursive_fallback(SYSTEMD_CGROUP_CONTROLLER, from, cgroup_controller_to_string(c), to, 0);
+                r = (r < 0) ? r : q;
+        }
+
+        return r;
+}
+
+int cg_trim_everywhere(CGroupMask supported, const char *path, bool delete_root) {
+        int r, q;
+
+        r = cg_trim(SYSTEMD_CGROUP_CONTROLLER, path, delete_root);
+        if (r < 0)
+                return r;
+
+        q = cg_all_unified();
+        if (q < 0)
+                return q;
+        if (q > 0)
+                return r;
+
+        return cg_trim_v1_controllers(supported, _CGROUP_MASK_ALL, path, delete_root);
+}
+
+int cg_trim_v1_controllers(CGroupMask supported, CGroupMask mask, const char *path, bool delete_root) {
+        CGroupController c;
+        CGroupMask done;
+        int r = 0, q;
+
+        supported &= CGROUP_MASK_V1;
+        mask = CGROUP_MASK_EXTEND_JOINED(mask);
+        done = 0;
+
+        for (c = 0; c < _CGROUP_CONTROLLER_MAX; c++) {
+                CGroupMask bit = CGROUP_CONTROLLER_TO_MASK(c);
+
+                if (!FLAGS_SET(supported, bit))
+                        continue;
+
+                if (FLAGS_SET(done, bit))
+                        continue;
+
+                if (FLAGS_SET(mask, bit)) {
+                        /* Remember first error and try continuing */
+                        q = cg_trim(cgroup_controller_to_string(c), path, delete_root);
+                        r = (r < 0) ? r : q;
+                }
+                done |= CGROUP_MASK_EXTEND_JOINED(bit);
+        }
+
+        return r;
+}
+
+int cg_enable_everywhere(
+                CGroupMask supported,
+                CGroupMask mask,
+                const char *p,
+                CGroupMask *ret_result_mask) {
+
+        _cleanup_fclose_ FILE *f = NULL;
+        _cleanup_free_ char *fs = NULL;
+        CGroupController c;
+        CGroupMask ret = 0;
+        int r;
+
+        assert(p);
+
+        if (supported == 0) {
+                if (ret_result_mask)
+                        *ret_result_mask = 0;
+                return 0;
+        }
+
+        r = cg_all_unified();
+        if (r < 0)
+                return r;
+        if (r == 0) {
+                /* On the legacy hierarchy there's no concept of "enabling" controllers in cgroups defined. Let's claim
+                 * complete success right away. (If you wonder why we return the full mask here, rather than zero: the
+                 * caller tends to use the returned mask later on to compare if all controllers where properly joined,
+                 * and if not requeues realization. This use is the primary purpose of the return value, hence let's
+                 * minimize surprises here and reduce triggers for re-realization by always saying we fully
+                 * succeeded.) */
+                if (ret_result_mask)
+                        *ret_result_mask = mask & supported & CGROUP_MASK_V2; /* If you wonder why we mask this with
+                                                                               * CGROUP_MASK_V2: The 'supported' mask
+                                                                               * might contain pure-V1 or BPF
+                                                                               * controllers, and we never want to
+                                                                               * claim that we could enable those with
+                                                                               * cgroup.subtree_control */
+                return 0;
+        }
+
+        r = cg_get_path(SYSTEMD_CGROUP_CONTROLLER, p, "cgroup.subtree_control", &fs);
+        if (r < 0)
+                return r;
+
+        for (c = 0; c < _CGROUP_CONTROLLER_MAX; c++) {
+                CGroupMask bit = CGROUP_CONTROLLER_TO_MASK(c);
+                const char *n;
+
+                if (!FLAGS_SET(CGROUP_MASK_V2, bit))
+                        continue;
+
+                if (!FLAGS_SET(supported, bit))
+                        continue;
+
+                n = cgroup_controller_to_string(c);
+                {
+                        char s[1 + strlen(n) + 1];
+
+                        s[0] = FLAGS_SET(mask, bit) ? '+' : '-';
+                        strcpy(s + 1, n);
+
+                        if (!f) {
+                                f = fopen(fs, "we");
+                                if (!f)
+                                        return log_debug_errno(errno, "Failed to open cgroup.subtree_control file of %s: %m", p);
+                        }
+
+                        r = write_string_stream(f, s, WRITE_STRING_FILE_DISABLE_BUFFER);
+                        if (r < 0) {
+                                log_debug_errno(r, "Failed to %s controller %s for %s (%s): %m",
+                                                FLAGS_SET(mask, bit) ? "enable" : "disable", n, p, fs);
+                                clearerr(f);
+
+                                /* If we can't turn off a controller, leave it on in the reported resulting mask. This
+                                 * happens for example when we attempt to turn off a controller up in the tree that is
+                                 * used down in the tree. */
+                                if (!FLAGS_SET(mask, bit) && r == -EBUSY) /* You might wonder why we check for EBUSY
+                                                                           * only here, and not follow the same logic
+                                                                           * for other errors such as EINVAL or
+                                                                           * EOPNOTSUPP or anything else. That's
+                                                                           * because EBUSY indicates that the
+                                                                           * controllers is currently enabled and
+                                                                           * cannot be disabled because something down
+                                                                           * the hierarchy is still using it. Any other
+                                                                           * error most likely means something like "I
+                                                                           * never heard of this controller" or
+                                                                           * similar. In the former case it's hence
+                                                                           * safe to assume the controller is still on
+                                                                           * after the failed operation, while in the
+                                                                           * latter case it's safer to assume the
+                                                                           * controller is unknown and hence certainly
+                                                                           * not enabled. */
+                                        ret |= bit;
+                        } else {
+                                /* Otherwise, if we managed to turn on a controller, set the bit reflecting that. */
+                                if (FLAGS_SET(mask, bit))
+                                        ret |= bit;
+                        }
+                }
+        }
+
+        /* Let's return the precise set of controllers now enabled for the cgroup. */
+        if (ret_result_mask)
+                *ret_result_mask = ret;
+
+        return 0;
+}