agetty: Reload only if it is really needed

If netlink event arrives and related escapes are part of issue, agetty
reloads and re-display the prompt. Reload is triggered not only by IP
address change, but also by IPv6 RAs. In some environments it causes
reload several times in a minute, and even complicates the login.

To prevent this, reload only if a real change appears.

This consists of:
split print_issue_file() to several functions:

eval_issue_file() prints issue to memory. It does not affect terminal in
any way.

print_issue_file() prints issue file from memory.

cmp_issue_file() compares the issue file and returns true, if reload is
needed.

The implementation requires additional change:

do_prompt() does not evaluate the issue file. It is responsibility of
calling function.

Test suite:

Use issue that contais \4 and/or \6 escape.

After installing new instance, restart agetty by typing a letter and then
Enter 6 times.

To check whether reload happens, type a letter. When reload happens,
letter disappears.

1. Unplug network cable. Wait a while and re-plug network cable.
You should see 2 reloads on single stack and 3 reloads on dual stack.

2. Run a loop
while : ; do
	sed -i '$areload_test' /etc/issue
	agetty --reload
	sleep 3
	sed -i '/reload_test/d' /etc/issue
	agetty --reload
	sleep 3
done
You should see regular reload every 3 seconds.

3. Run a loop
while : ; do
	agetty --reload
	sleep 3
done
Before: You see regular reload every 3 seconds.
After: No reloads.

4. Run a loop
while : ; do
	ifconfig lo 127.0.0.1 netmask 255.0.0.0
	sleep 3
	ifconfig lo 127.0.0.2 netmask 255.0.0.0
	sleep 3
done
Before: You see regular reload every 3 seconds.
After: No reloads.

Signed-off-by: Stanislav Brabec <sbrabec@suse.cz>

diff --git a/term-utils/agetty.c b/term-utils/agetty.c
index 137add46535973fbe40952d7d74c1d19a81fdb42..b885b4975281ed3c8229eb3f09afd6499f6cd2b0 100644 (file)
--- a/term-utils/agetty.c
+++ b/term-utils/agetty.c
@@ -28,6 +28,7 @@
 #include <utmpx.h>
 #include <getopt.h>
 #include <time.h>
+#include <stdbool.h>
 #include <sys/socket.h>
 #include <langinfo.h>
 #include <grp.h>
@@ -328,6 +329,7 @@ static void check_username (const char* nm);
 static void login_options_to_argv(char *argv[], int *argc, char *str, char *username);
 static void reload_agettys(void);
 static void print_issue_file(struct options *op, struct termios *tp);
+static void eval_issue_file(struct options *op, struct termios *tp);
 
 /* Fake hostname for ut_host specified on command line. */
 static char *fakehost;
@@ -463,10 +465,12 @@ int main(int argc, char **argv)
        }
 
        if (options.flags & F_NOPROMPT) {       /* --skip-login */
+               eval_issue_file(&options, &termios);
                print_issue_file(&options, &termios);
        } else {                                /* regular (auto)login */
                if (options.autolog) {
                        /* Autologin prompt */
+                       eval_issue_file(&options, &termios);
                        do_prompt(&options, &termios);
                        printf(_("%s%s (automatic login)\n"), LOGIN, options.autolog);
                } else {
@@ -1730,9 +1734,66 @@ static void print_issue_file(struct options *op, struct termios *tp __attribute_
                write_all(STDOUT_FILENO, "\r\n", 2);
        }
 }
+static void eval_issue_file(struct options *op __attribute__((__unused__)), struct termios *tp __attribute__((__unused__)))
+{
+}
 #else /* ISSUE_SUPPORT */
 
+static FILE *issue_f;
+static char *issue_mem = NULL;
+static size_t issue_mem_sz;
+static bool do_tcsetattr;
+static bool do_tcrestore;
+#ifdef AGETTY_RELOAD
+static char *issue_mem_old = NULL;
+#endif
+static bool cmp_issue_file(void) {
+       if (issue_mem_old && issue_mem) {
+               if (!strcmp(issue_mem_old, issue_mem)) {
+                       free(issue_mem_old);
+                       issue_mem_old = issue_mem;
+                       issue_mem = NULL;
+                       return false;
+               }
+       } else
+               return true;
+       return true;
+}
 static void print_issue_file(struct options *op, struct termios *tp)
+{
+       int oflag = tp->c_oflag;            /* Save current setting. */
+
+       if ((op->flags & F_NONL) == 0) {
+               /* Issue not in use, start with a new line. */
+               write_all(STDOUT_FILENO, "\r\n", 2);
+       }
+
+       if (do_tcsetattr) {
+               if ((op->flags & F_VCONSOLE) == 0) {
+                       /* Map new line in output to carriage return & new line. */
+                       tp->c_oflag |= (ONLCR | OPOST);
+                       tcsetattr(STDIN_FILENO, TCSADRAIN, tp);
+               }
+       }
+
+       write_all(STDOUT_FILENO, issue_mem, issue_mem_sz);
+       if (do_tcrestore) {
+               /* Restore settings. */
+               tp->c_oflag = oflag;
+               /* Wait till output is gone. */
+               tcsetattr(STDIN_FILENO, TCSADRAIN, tp);
+       }
+#ifdef AGETTY_RELOAD
+       free(issue_mem_old);
+       issue_mem_old = issue_mem;
+       issue_mem = NULL;
+#else
+       free(issue_mem);
+       issue_mem = NULL;
+#endif
+}
+
+static void eval_issue_file(struct options *op, struct termios *tp)
 {
        const char *filename, *dirname = NULL;
        FILE *f = NULL;
@@ -1743,10 +1804,6 @@ static void print_issue_file(struct options *op, struct termios *tp)
 #ifdef AGETTY_RELOAD
        netlink_groups = 0;
 #endif
-       if ((op->flags & F_NONL) == 0) {
-               /* Issue not in use, start with a new line. */
-               write_all(STDOUT_FILENO, "\r\n", 2);
-       }
 
        if (!(op->flags & F_ISSUE))
                return;
@@ -1777,6 +1834,7 @@ static void print_issue_file(struct options *op, struct termios *tp)
                dirname = _PATH_ISSUEDIR;
        }
 
+       issue_f = open_memstream(&issue_mem, &issue_mem_sz);
 #ifdef ISSUEDIR_SUPPORT
        if (dirname) {
                dd = open(dirname, O_RDONLY|O_CLOEXEC|O_DIRECTORY);
@@ -1791,13 +1849,9 @@ static void print_issue_file(struct options *op, struct termios *tp)
                f = fopen(filename, "r");
 
        if (f || dirname) {
-               int c, oflag = tp->c_oflag;         /* Save current setting. */
+               int c;
 
-               if ((op->flags & F_VCONSOLE) == 0) {
-                       /* Map new line in output to carriage return & new line. */
-                       tp->c_oflag |= (ONLCR | OPOST);
-                       tcsetattr(STDIN_FILENO, TCSADRAIN, tp);
-               }
+               do_tcsetattr = true;
 
                do {
 #ifdef ISSUEDIR_SUPPORT
@@ -1810,7 +1864,7 @@ static void print_issue_file(struct options *op, struct termios *tp)
                                if (c == '\\')
                                        output_special_char(getc(f), op, tp, f);
                                else
-                                       putchar(c);
+                                       putc(c, issue_f);
                        }
                        fclose(f);
                        f = NULL;
@@ -1818,12 +1872,8 @@ static void print_issue_file(struct options *op, struct termios *tp)
 
                fflush(stdout);
 
-               if ((op->flags & F_VCONSOLE) == 0) {
-                       /* Restore settings. */
-                       tp->c_oflag = oflag;
-                       /* Wait till output is gone. */
-                       tcsetattr(STDIN_FILENO, TCSADRAIN, tp);
-               }
+               if ((op->flags & F_VCONSOLE) == 0)
+                       do_tcrestore = true;
        }
 
 #ifdef ISSUEDIR_SUPPORT
@@ -1837,6 +1887,7 @@ static void print_issue_file(struct options *op, struct termios *tp)
        if (netlink_groups != 0)
                open_netlink();
 #endif
+       fclose(issue_f);
 }
 #endif /* ISSUE_SUPPORT */
 
@@ -1851,11 +1902,14 @@ again:
        if (op->flags & F_LOGINPAUSE) {
                puts(_("[press ENTER to login]"));
 #ifdef AGETTY_RELOAD
+               /* reload issue */
                if (!wait_for_term_input(STDIN_FILENO)) {
-                       /* reload issue */
-                       if (op->flags & F_VCONSOLE)
-                               termio_clear(STDOUT_FILENO);
-                       goto again;
+                       eval_issue_file(op, tp);
+                       if (cmp_issue_file()) {
+                               if (op->flags & F_VCONSOLE)
+                                       termio_clear(STDOUT_FILENO);
+                               goto again;
+                       }
                }
 #endif
                getc(stdin);
@@ -1976,17 +2030,22 @@ static char *get_logname(struct options *op, struct termios *tp, struct chardata
        bp = logname;
        *bp = '\0';
 
+       eval_issue_file(op, tp);
        while (*logname == '\0') {
                /* Write issue file and prompt */
                do_prompt(op, tp);
 
 #ifdef AGETTY_RELOAD
+       no_reload:
                if (!wait_for_term_input(STDIN_FILENO)) {
                        /* refresh prompt -- discard input data, clear terminal
                         * and call do_prompt() again
                         */
                        if ((op->flags & F_VCONSOLE) == 0)
                                sleep(1);
+                       eval_issue_file(op, tp);
+                       if (!cmp_issue_file())
+                               goto no_reload;
                        tcflush(STDIN_FILENO, TCIFLUSH);
                        if (op->flags & F_VCONSOLE)
                                termio_clear(STDOUT_FILENO);
@@ -2374,7 +2433,7 @@ static void print_addr(sa_family_t family, void *addr)
        char buff[INET6_ADDRSTRLEN + 1];
 
        inet_ntop(family, addr, buff, sizeof(buff));
-       printf("%s", buff);
+       fprintf(issue_f, "%s", buff);
 }
 
 /*
@@ -2496,36 +2555,36 @@ static void output_special_char(unsigned char c, struct options *op,
                if (get_escape_argument(fp, escname, sizeof(escname))) {
                        const char *esc = color_sequence_from_colorname(escname);
                        if (esc)
-                               fputs(esc, stdout);
+                               fputs(esc, issue_f);
                } else
-                       fputs("\033", stdout);
+                       fputs("\033", issue_f);
                break;
        }
        case 's':
                uname(&uts);
-               printf("%s", uts.sysname);
+               fprintf(issue_f, "%s", uts.sysname);
                break;
        case 'n':
                uname(&uts);
-               printf("%s", uts.nodename);
+               fprintf(issue_f, "%s", uts.nodename);
                break;
        case 'r':
                uname(&uts);
-               printf("%s", uts.release);
+               fprintf(issue_f, "%s", uts.release);
                break;
        case 'v':
                uname(&uts);
-               printf("%s", uts.version);
+               fprintf(issue_f, "%s", uts.version);
                break;
        case 'm':
                uname(&uts);
-               printf("%s", uts.machine);
+               fprintf(issue_f, "%s", uts.machine);
                break;
        case 'o':
        {
                char *dom = xgetdomainname();
 
-               fputs(dom ? dom : "unknown_domain", stdout);
+               fputs(dom ? dom : "unknown_domain", issue_f);
                free(dom);
                break;
        }
@@ -2545,7 +2604,7 @@ static void output_special_char(unsigned char c, struct options *op,
                            (canon = strchr(info->ai_canonname, '.')))
                                dom = canon + 1;
                }
-               fputs(dom ? dom : "unknown_domain", stdout);
+               fputs(dom ? dom : "unknown_domain", issue_f);
                if (info)
                        freeaddrinfo(info);
                free(host);
@@ -2564,19 +2623,19 @@ static void output_special_char(unsigned char c, struct options *op,
                        break;
 
                if (c == 'd') /* ISO 8601 */
-                       printf("%s %s %d  %d",
+                       fprintf(issue_f, "%s %s %d  %d",
                                      nl_langinfo(ABDAY_1 + tm->tm_wday),
                                      nl_langinfo(ABMON_1 + tm->tm_mon),
                                      tm->tm_mday,
                                      tm->tm_year < 70 ? tm->tm_year + 2000 :
                                      tm->tm_year + 1900);
                else
-                       printf("%02d:%02d:%02d",
+                       fprintf(issue_f, "%02d:%02d:%02d",
                                      tm->tm_hour, tm->tm_min, tm->tm_sec);
                break;
        }
        case 'l':
-               printf ("%s", op->tty);
+               fprintf (issue_f, "%s", op->tty);
                break;
        case 'b':
        {
@@ -2585,7 +2644,7 @@ static void output_special_char(unsigned char c, struct options *op,
 
                for (i = 0; speedtab[i].speed; i++) {
                        if (speedtab[i].code == speed) {
-                               printf("%ld", speedtab[i].speed);
+                               fprintf(issue_f, "%ld", speedtab[i].speed);
                                break;
                        }
                }
@@ -2600,18 +2659,18 @@ static void output_special_char(unsigned char c, struct options *op,
                        var = read_os_release(op, varname);
                        if (var) {
                                if (strcmp(varname, "ANSI_COLOR") == 0)
-                                       printf("\033[%sm", var);
+                                       fprintf(issue_f, "\033[%sm", var);
                                else
-                                       fputs(var, stdout);
+                                       fputs(var, issue_f);
                        }
                /* \S */
                } else if ((var = read_os_release(op, "PRETTY_NAME"))) {
-                       fputs(var, stdout);
+                       fputs(var, issue_f);
 
                /* \S and PRETTY_NAME not found */
                } else {
                        uname(&uts);
-                       fputs(uts.sysname, stdout);
+                       fputs(uts.sysname, issue_f);
                }
 
                free(var);
@@ -2629,9 +2688,9 @@ static void output_special_char(unsigned char c, struct options *op,
                                users++;
                endutxent();
                if (c == 'U')
-                       printf(P_("%d user", "%d users", users), users);
+                       fprintf(issue_f, P_("%d user", "%d users", users), users);
                else
-                       printf ("%d ", users);
+                       fprintf (issue_f, "%d ", users);
                break;
        }
        case '4':