env-util: add new setenvf() helper

And convert some pieces of code over.

src/basic/env-util.c

@@ -1012,8 +1012,8 @@ int putenv_dup(const char *assignment, bool override) {
 }
 
 int setenv_systemd_exec_pid(bool update_only) {
-        char str[DECIMAL_STR_MAX(pid_t)];
         const char *e;
+        int r;
 
         /* Update $SYSTEMD_EXEC_PID=pid except when '*' is set for the variable. */
 
@@ -1024,10 +1024,9 @@ int setenv_systemd_exec_pid(bool update_only) {
         if (streq_ptr(e, "*"))
                 return 0;
 
-        xsprintf(str, PID_FMT, getpid_cached());
-
-        if (setenv("SYSTEMD_EXEC_PID", str, 1) < 0)
-                return -errno;
+        r = setenvf("SYSTEMD_EXEC_PID", /* overwrite= */ 1, PID_FMT, getpid_cached());
+        if (r < 0)
+                return r;
 
         return 1;
 }
@@ -1122,3 +1121,25 @@ int set_full_environment(char **env) {
 
         return 0;
 }
+
+int setenvf(const char *name, bool overwrite, const char *valuef, ...) {
+        _cleanup_free_ char *value = NULL;
+        va_list ap;
+        int r;
+
+        assert(name);
+
+        if (!valuef)
+                return RET_NERRNO(unsetenv(name));
+
+        va_start(ap, valuef);
+        DISABLE_WARNING_FORMAT_NONLITERAL;
+        r = vasprintf(&value, valuef, ap);
+        REENABLE_WARNING;
+        va_end(ap);
+
+        if (r < 0)
+                return -ENOMEM;
+
+        return RET_NERRNO(setenv(name, value, overwrite));
+}

src/basic/env-util.h

@@ -80,3 +80,5 @@ int getenv_path_list(const char *name, char ***ret_paths);
 int getenv_steal_erase(const char *name, char **ret);
 
 int set_full_environment(char **env);
+
+int setenvf(const char *name, bool overwrite, const char *valuef, ...) _printf_(3,4);

src/journal/cat.c

@@ -12,6 +12,7 @@
 
 #include "alloc-util.h"
 #include "build.h"
+#include "env-util.h"
 #include "fd-util.h"
 #include "format-util.h"
 #include "main-func.h"
@@ -157,7 +158,6 @@ static int run(int argc, char *argv[]) {
         if (argc <= optind)
                 (void) execl("/bin/cat", "/bin/cat", NULL);
         else {
-                _cleanup_free_ char *s = NULL;
                 struct stat st;
 
                 if (fstat(STDERR_FILENO, &st) < 0)
@@ -165,11 +165,9 @@ static int run(int argc, char *argv[]) {
                                                "Failed to fstat(%s): %m",
                                                FORMAT_PROC_FD_PATH(STDERR_FILENO));
 
-                if (asprintf(&s, DEV_FMT ":" INO_FMT, (dev_t)st.st_dev, st.st_ino) < 0)
-                        return log_oom();
-
-                if (setenv("JOURNAL_STREAM", s, /* overwrite = */ true) < 0)
-                        return log_error_errno(errno, "Failed to set environment variable JOURNAL_STREAM: %m");
+                r = setenvf("JOURNAL_STREAM", /* overwrite = */ true, DEV_FMT ":" INO_FMT, (dev_t) st.st_dev, st.st_ino);
+                if (r < 0)
+                        return log_error_errno(r, "Failed to set environment variable JOURNAL_STREAM: %m");
 
                 (void) execvp(argv[optind], argv + optind);
         }

src/userdb/userdbd-manager.c

@@ -5,6 +5,7 @@
 #include "sd-daemon.h"
 
 #include "common-signal.h"
+#include "env-util.h"
 #include "fd-util.h"
 #include "fs-util.h"
 #include "mkdir.h"
@@ -157,7 +158,6 @@ static int start_one_worker(Manager *m) {
         if (r < 0)
                 return log_error_errno(r, "Failed to fork new worker child: %m");
         if (r == 0) {
-                char pids[DECIMAL_STR_MAX(pid_t)];
                 /* Child */
 
                 if (m->listen_fd == 3) {
@@ -175,9 +175,9 @@ static int start_one_worker(Manager *m) {
                         safe_close(m->listen_fd);
                 }
 
-                xsprintf(pids, PID_FMT, pid);
-                if (setenv("LISTEN_PID", pids, 1) < 0) {
-                        log_error_errno(errno, "Failed to set $LISTEN_PID: %m");
+                r = setenvf("LISTEN_PID", /* overwrite= */ true, PID_FMT, pid);
+                if (r < 0) {
+                        log_error_errno(r, "Failed to set $LISTEN_PID: %m");
                         _exit(EXIT_FAILURE);
                 }