core: optionally create LOGIN_PROCESS or USER_PROCESS utmp entries

When generating utmp/wtmp entries, optionally add both LOGIN_PROCESS and
INIT_PROCESS entries or even all three of LOGIN_PROCESS, INIT_PROCESS
and USER_PROCESS entries, instead of just a single INIT_PROCESS entry.

With this change systemd may be used to not only invoke a getty directly
in a SysV-compliant way but alternatively also a login(1) implementation
or even forego getty and login entirely, and invoke arbitrary shells in
a way that they appear in who(1) or w(1).

This is preparation for a later commit that adds a "machinectl shell"
operation to invoke a shell in a container, in a way that is compatible
with who(1) and w(1).

2 files changed, 24 insertions, 4 deletions

diff --git a/src/shared/utmp-wtmp.c b/src/shared/utmp-wtmp.c
index 8f66df7718..63f1e4ca6f 100644
--- a/src/shared/utmp-wtmp.c
+++ b/src/shared/utmp-wtmp.c
@@ -204,12 +204,13 @@ _pure_ static const char *sanitize_id(const char *id) {
         return id + l - sizeof(((struct utmpx*) NULL)->ut_id);
 }
 
-int utmp_put_init_process(const char *id, pid_t pid, pid_t sid, const char *line) {
+int utmp_put_init_process(const char *id, pid_t pid, pid_t sid, const char *line, int ut_type, const char *user) {
         struct utmpx store = {
                 .ut_type = INIT_PROCESS,
                 .ut_pid = pid,
                 .ut_session = sid,
         };
+        int r;
 
         assert(id);
 
@@ -221,7 +222,26 @@ int utmp_put_init_process(const char *id, pid_t pid, pid_t sid, const char *line
         if (line)
                 strncpy(store.ut_line, basename(line), sizeof(store.ut_line));
 
-        return write_entry_both(&store);
+        r = write_entry_both(&store);
+        if (r < 0)
+                return r;
+
+        if (ut_type == LOGIN_PROCESS || ut_type == USER_PROCESS) {
+                store.ut_type = LOGIN_PROCESS;
+                r = write_entry_both(&store);
+                if (r < 0)
+                        return r;
+        }
+
+        if (ut_type == USER_PROCESS) {
+                store.ut_type = USER_PROCESS;
+                strncpy(store.ut_user, user, sizeof(store.ut_user)-1);
+                r = write_entry_both(&store);
+                if (r < 0)
+                        return r;
+        }
+
+        return 0;
 }
 
 int utmp_put_dead_process(const char *id, pid_t pid, int code, int status) {
diff --git a/src/shared/utmp-wtmp.h b/src/shared/utmp-wtmp.h
index 5d26ba6fb1..e0ceb873ac 100644
--- a/src/shared/utmp-wtmp.h
+++ b/src/shared/utmp-wtmp.h
@@ -31,7 +31,7 @@ int utmp_put_reboot(usec_t timestamp);
 int utmp_put_runlevel(int runlevel, int previous);
 
 int utmp_put_dead_process(const char *id, pid_t pid, int code, int status);
-int utmp_put_init_process(const char *id, pid_t pid, pid_t sid, const char *line);
+int utmp_put_init_process(const char *id, pid_t pid, pid_t sid, const char *line, int ut_type, const char *user);
 
 int utmp_wall(
         const char *message,
@@ -57,7 +57,7 @@ static inline int utmp_put_runlevel(int runlevel, int previous) {
 static inline int utmp_put_dead_process(const char *id, pid_t pid, int code, int status) {
         return 0;
 }
-static inline int utmp_put_init_process(const char *id, pid_t pid, pid_t sid, const char *line) {
+static inline int utmp_put_init_process(const char *id, pid_t pid, pid_t sid, const char *line, int ut_type, const char *user) {
         return 0;
 }
 static inline int utmp_wall(