machine-id-setup: add a machine_id_commit call to commit on disk a transient machine-id

If /etc was read only at boot time with an empty /etc/machine-id, the latter
will be mounted as a tmpfs and get reset at each boot. If the system becomes rw
later, this functionality enables to commit in a race-free manner the
transient machine-id to disk.

2 files changed, 11 insertions, 0 deletions

diff --git a/src/shared/util.c b/src/shared/util.c
index 21651708d5..4fcbab97be 100644
--- a/src/shared/util.c
+++ b/src/shared/util.c
@@ -3052,6 +3052,15 @@ _pure_ static int is_temporary_fs(struct statfs *s) {
                F_TYPE_EQUAL(s->f_type, RAMFS_MAGIC);
 }
 
+int is_fd_on_temporary_fs(int fd) {
+        struct statfs s;
+
+        if (fstatfs(fd, &s) < 0)
+                return -errno;
+
+        return is_temporary_fs(&s);
+}
+
 int rm_rf_children(int fd, bool only_dirs, bool honour_sticky, struct stat *root_dev) {
         struct statfs s;
 
diff --git a/src/shared/util.h b/src/shared/util.h
index b53a45da9d..0b7c77b1d4 100644
--- a/src/shared/util.h
+++ b/src/shared/util.h
@@ -454,6 +454,8 @@ int get_ctty(pid_t, dev_t *_devnr, char **r);
 int chmod_and_chown(const char *path, mode_t mode, uid_t uid, gid_t gid);
 int fchmod_and_fchown(int fd, mode_t mode, uid_t uid, gid_t gid);
 
+int is_fd_on_temporary_fs(int fd);
+
 int rm_rf_children(int fd, bool only_dirs, bool honour_sticky, struct stat *root_dev);
 int rm_rf_children_dangerous(int fd, bool only_dirs, bool honour_sticky, struct stat *root_dev);
 int rm_rf(const char *path, bool only_dirs, bool delete_root, bool honour_sticky);