From b2dcfd8e11977d4369560b8b4de81b947b0e963e Mon Sep 17 00:00:00 2001
From: Lennart Poettering <lennart@poettering.net>
Date: Tue, 12 Dec 2023 11:02:59 +0100
Subject: [PATCH] cgroup-setup: add fd-based version of cg_attach()

---
 src/shared/cgroup-setup.c | 14 ++++++++++++++
 src/shared/cgroup-setup.h |  1 +
 2 files changed, 15 insertions(+)

diff --git a/src/shared/cgroup-setup.c b/src/shared/cgroup-setup.c
index d9cca6ced4..f82af4cf43 100644
--- a/src/shared/cgroup-setup.c
+++ b/src/shared/cgroup-setup.c
@@ -384,6 +384,20 @@ int cg_attach(const char *controller, const char *path, pid_t pid) {
         return 0;
 }
 
+int cg_fd_attach(int fd, pid_t pid) {
+        char c[DECIMAL_STR_MAX(pid_t) + 2];
+
+        assert(fd >= 0);
+        assert(pid >= 0);
+
+        if (pid == 0)
+                pid = getpid_cached();
+
+        xsprintf(c, PID_FMT "\n", pid);
+
+        return write_string_file_at(fd, "cgroup.procs", c, WRITE_STRING_FILE_DISABLE_BUFFER);
+}
+
 int cg_attach_fallback(const char *controller, const char *path, pid_t pid) {
         int r;
 
diff --git a/src/shared/cgroup-setup.h b/src/shared/cgroup-setup.h
index c35884ee4d..283ab6757c 100644
--- a/src/shared/cgroup-setup.h
+++ b/src/shared/cgroup-setup.h
@@ -21,6 +21,7 @@ int cg_trim(const char *controller, const char *path, bool delete_root);
 
 int cg_create(const char *controller, const char *path);
 int cg_attach(const char *controller, const char *path, pid_t pid);
+int cg_fd_attach(int fd, pid_t pid);
 int cg_attach_fallback(const char *controller, const char *path, pid_t pid);
 int cg_create_and_attach(const char *controller, const char *path, pid_t pid);