libbb: split update_utmp from login/getty in preparation to use it for telnetd

function                                             old     new   delta
update_utent                                           -     339    +339
login_main                                          1498    1128    -370
------------------------------------------------------------------------------
(add/remove: 1/0 grow/shrink: 0/1 up/down: 339/-370)          Total: -31 bytes

function                                             old     new   delta
update_utmp                                          246     337     +91
login_main                                          1128    1140     +12
getty_main                                          1908    1918     +10
...
update_utent                                         339       -    -339
------------------------------------------------------------------------------
(add/remove: 1/1 grow/shrink: 5/6 up/down: 119/-368)         Total: -249 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 92 insertions, 0 deletions

diff --git a/libbb/utmp.c b/libbb/utmp.c
new file mode 100644
index 000000000..06b939b9d
--- /dev/null
+++ b/libbb/utmp.c
@@ -0,0 +1,92 @@
+/* vi: set sw=4 ts=4: */
+/*
+ * utmp/wtmp support routines.
+ *
+ * Copyright (C) 2010 Denys Vlasenko
+ *
+ * Licensed under GPL version 2, see file LICENSE in this tarball for details.
+ */
+#include "libbb.h"
+#include <utmp.h>
+
+static void touch(const char *filename)
+{
+	if (access(filename, R_OK | W_OK) == -1)
+		close(open(filename, O_WRONLY | O_CREAT, 0664));
+}
+
+/*
+ * Read "man utmp" to make sense out of it.
+ */
+void FAST_FUNC update_utmp(int new_type, const char *short_tty, const char *username, const char *opt_host)
+{
+	struct utmp utent;
+	struct utmp *ut;
+	pid_t pid;
+
+	touch(_PATH_UTMP);
+	utmpname(_PATH_UTMP);
+	setutent();
+
+	pid = getpid();
+	/* Did init/getty/telnetd/sshd/... create an entry for us?
+	 * It should be (new_type-1), but we'd also reuse
+	 * any other potentially stale xxx_PROCESS entry */
+	while ((ut = getutent()) != NULL) {
+		if (ut->ut_pid == pid
+		// && ut->ut_line[0]
+		 && ut->ut_id[0] /* must have nonzero id */
+		 && (  ut->ut_type == INIT_PROCESS
+		    || ut->ut_type == LOGIN_PROCESS
+		    || ut->ut_type == USER_PROCESS
+		    || ut->ut_type == DEAD_PROCESS
+		    )
+		) {
+			utent = *ut; /* struct copy */
+			if (ut->ut_type >= new_type) {
+				/* Stale record. Nuke hostname */
+				memset(utent.ut_host, 0, sizeof(utent.ut_host));
+			}
+			/* NB: pututline (see later) searches for matching utent
+			 * using getutid(utent) - we must not change ut_id
+			 * if we want *exactly this* record to be overwritten!
+			 */
+			break;
+		}
+	}
+	endutent();
+
+	if (!ut) {
+		/* Didn't find anything, create new one */
+		memset(&utent, 0, sizeof(utent));
+		utent.ut_pid = pid;
+		/* Invent our own ut_id. ut_id is only 4 chars wide.
+		 * Try to fit something remotely meaningful... */
+		if (short_tty[0] == 'p') {
+			/* if "ptyXXX", map to "pXXX" */
+			/* if "pts/XX", map to "p/XX" */
+			utent.ut_id[0] = 'p';
+			strncpy(utent.ut_id + 1, short_tty + 3, sizeof(utent.ut_id)-1);
+		} else {
+			/* assuming it's "ttyXXXX", map to "XXXX" */
+			strncpy(utent.ut_id, short_tty + 3, sizeof(utent.ut_id));
+		}
+	}
+
+	utent.ut_type = new_type;
+	safe_strncpy(utent.ut_line, short_tty, sizeof(utent.ut_line));
+	safe_strncpy(utent.ut_user, username, sizeof(utent.ut_user));
+	if (opt_host)
+		safe_strncpy(utent.ut_host, opt_host, sizeof(utent.ut_host));
+	utent.ut_tv.tv_sec = time(NULL);
+
+	/* Update, or append new one */
+	setutent();
+	pututline(&utent);
+	endutent();
+
+#if ENABLE_FEATURE_WTMP
+	touch(bb_path_wtmp_file);
+	updwtmp(bb_path_wtmp_file, &utent);
+#endif
+}