journal: expose and make use of cutoff times of journal

This helps explaining when the log output of "systemctl status" is
incomplete because the logs got rotated since the service was started.

src/journal/journal-def.h

@@ -160,8 +160,8 @@ _packed_ struct Header {
         uint8_t state;
         uint8_t reserved[7];
         sd_id128_t file_id;
-        sd_id128_t machine_id;
-        sd_id128_t boot_id;
+        sd_id128_t machine_id; /* last writer */
+        sd_id128_t boot_id;    /* last writer */
         sd_id128_t seqnum_id;
         le64_t header_size;
         le64_t arena_size;

src/journal/journal-file.c

@@ -183,6 +183,7 @@ static int journal_file_verify_header(JournalFile *f) {
 
                 if (state == STATE_ONLINE)
                         log_debug("Journal file %s is already online. Assuming unclean closing. Ignoring.", f->path);
+                        /* FIXME: immediately rotate */
                 else if (state == STATE_ARCHIVED)
                         return -ESHUTDOWN;
                 else if (state != STATE_OFFLINE)
@@ -2284,3 +2285,74 @@ void journal_default_metrics(JournalMetrics *m, int fd) {
                  format_bytes(c, sizeof(c), m->min_size),
                  format_bytes(d, sizeof(d), m->keep_free));
 }
+
+int journal_file_get_cutoff_realtime_usec(JournalFile *f, usec_t *from, usec_t *to) {
+        Object *o;
+        int r;
+
+        assert(f);
+        assert(from || to);
+
+        if (from) {
+                r = journal_file_next_entry(f, NULL, 0, DIRECTION_DOWN, &o, NULL);
+                if (r <= 0)
+                        return r;
+
+                *from = le64toh(o->entry.realtime);
+        }
+
+        if (to) {
+                r = journal_file_next_entry(f, NULL, 0, DIRECTION_UP, &o, NULL);
+                if (r <= 0)
+                        return r;
+
+                *to = le64toh(o->entry.realtime);
+        }
+
+        return 1;
+}
+
+int journal_file_get_cutoff_monotonic_usec(JournalFile *f, sd_id128_t boot_id, usec_t *from, usec_t *to) {
+        char t[9+32+1] = "_BOOT_ID=";
+        Object *o;
+        uint64_t p;
+        int r;
+
+        assert(f);
+        assert(from || to);
+
+        sd_id128_to_string(boot_id, t + 9);
+
+        r = journal_file_find_data_object(f, t, strlen(t), &o, &p);
+        if (r <= 0)
+                return r;
+
+        if (le64toh(o->data.n_entries) <= 0)
+                return 0;
+
+        if (from) {
+                r = journal_file_move_to_object(f, OBJECT_ENTRY, le64toh(o->data.entry_offset), &o);
+                if (r < 0)
+                        return r;
+
+                *from = le64toh(o->entry.monotonic);
+        }
+
+        if (to) {
+                r = journal_file_move_to_object(f, OBJECT_DATA, p, &o);
+                if (r < 0)
+                        return r;
+
+                r = generic_array_get_plus_one(f,
+                                               le64toh(o->data.entry_offset),
+                                               le64toh(o->data.entry_array_offset),
+                                               le64toh(o->data.n_entries)-1,
+                                               &o, NULL);
+                if (r <= 0)
+                        return r;
+
+                *to = le64toh(o->entry.monotonic);
+        }
+
+        return 1;
+}

src/journal/journal-file.h

@@ -125,4 +125,7 @@ void journal_file_post_change(JournalFile *f);
 
 void journal_default_metrics(JournalMetrics *m, int fd);
 
+int journal_file_get_cutoff_realtime_usec(JournalFile *f, usec_t *from, usec_t *to);
+int journal_file_get_cutoff_monotonic_usec(JournalFile *f, sd_id128_t boot, usec_t *from, usec_t *to);
+
 #endif

src/journal/journalctl.c

@@ -281,6 +281,26 @@ int main(int argc, char *argv[]) {
                 goto finish;
         }
 
+        if (!arg_quiet) {
+                usec_t start, end;
+                char start_buf[FORMAT_TIMESTAMP_MAX], end_buf[FORMAT_TIMESTAMP_MAX];
+
+                r = sd_journal_get_cutoff_realtime_usec(j, &start, &end);
+                if (r < 0) {
+                        log_error("Failed to get cutoff: %s", strerror(-r));
+                        goto finish;
+                }
+
+                if (r > 0) {
+                        if (arg_follow)
+                                printf("Logs begin at %s.\n", format_timestamp(start_buf, sizeof(start_buf), start));
+                        else
+                                printf("Logs begin at %s, end at %s.\n",
+                                       format_timestamp(start_buf, sizeof(start_buf), start),
+                                       format_timestamp(end_buf, sizeof(end_buf), end));
+                }
+        }
+
         if (arg_lines >= 0) {
                 r = sd_journal_seek_tail(j);
                 if (r < 0) {

src/journal/libsystemd-journal.sym

@@ -51,3 +51,9 @@ global:
         sd_journal_send_with_location;
         sd_journal_sendv_with_location;
 } LIBSYSTEMD_JOURNAL_38;
+
+LIBSYSTEMD_JOURNAL_184 {
+global:
+        sd_journal_get_cutoff_realtime_usec;
+        sd_journal_get_cutoff_monotonic_usec;
+} LIBSYSTEMD_JOURNAL_183;

src/journal/sd-journal.c

@@ -1620,6 +1620,81 @@ _public_ int sd_journal_process(sd_journal *j) {
         }
 }
 
+_public_ int sd_journal_get_cutoff_realtime_usec(sd_journal *j, uint64_t *from, uint64_t *to) {
+        Iterator i;
+        JournalFile *f;
+        bool first = true;
+        int r;
+
+        if (!j)
+                return -EINVAL;
+        if (!from && !to)
+                return -EINVAL;
+
+        HASHMAP_FOREACH(f, j->files, i) {
+                usec_t fr, t;
+
+                r = journal_file_get_cutoff_realtime_usec(f, &fr, &t);
+                if (r < 0)
+                        return r;
+                if (r == 0)
+                        continue;
+
+                if (first) {
+                        if (from)
+                                *from = fr;
+                        if (to)
+                                *to = t;
+                        first = false;
+                } else {
+                        if (from)
+                                *from = MIN(fr, *from);
+                        if (to)
+                                *to = MIN(t, *to);
+                }
+        }
+
+        return first ? 0 : 1;
+}
+
+_public_ int sd_journal_get_cutoff_monotonic_usec(sd_journal *j, sd_id128_t boot_id, uint64_t *from, uint64_t *to) {
+        Iterator i;
+        JournalFile *f;
+        bool first = true;
+        int r;
+
+        if (!j)
+                return -EINVAL;
+        if (!from && !to)
+                return -EINVAL;
+
+        HASHMAP_FOREACH(f, j->files, i) {
+                usec_t fr, t;
+
+                r = journal_file_get_cutoff_monotonic_usec(f, boot_id, &fr, &t);
+                if (r < 0)
+                        return r;
+                if (r == 0)
+                        continue;
+
+                if (first) {
+                        if (from)
+                                *from = fr;
+                        if (to)
+                                *to = t;
+                        first = false;
+                } else {
+                        if (from)
+                                *from = MIN(fr, *from);
+                        if (to)
+                                *to = MIN(t, *to);
+                }
+        }
+
+        return first ? 0 : 1;
+}
+
+
 /* _public_ int sd_journal_query_unique(sd_journal *j, const char *field) { */
 /*         if (!j) */
 /*                 return -EINVAL; */

src/shared/logs-show.c

@@ -551,7 +551,8 @@ int show_journal_by_unit(
                 usec_t not_before,
                 unsigned how_many,
                 bool show_all,
-                bool follow) {
+                bool follow,
+                bool warn_cutoff) {
 
         char *m = NULL;
         sd_journal *j = NULL;
@@ -639,6 +640,26 @@ int show_journal_by_unit(
                                 goto finish;
                 }
 
+                if (warn_cutoff && line < how_many && not_before > 0) {
+                        sd_id128_t boot_id;
+                        usec_t cutoff;
+
+                        /* Check whether the cutoff line is too early */
+
+                        r = sd_id128_get_boot(&boot_id);
+                        if (r < 0)
+                                goto finish;
+
+                        r = sd_journal_get_cutoff_monotonic_usec(j, boot_id, &cutoff, NULL);
+                        if (r < 0)
+                                goto finish;
+
+                        if (not_before < cutoff)
+                                printf("Warning: Journal has been rotated since unit was started. Log output is incomplete or unavailable.\n");
+
+                        warn_cutoff = false;
+                }
+
                 if (!follow)
                         break;
 

src/shared/logs-show.h

@@ -48,7 +48,8 @@ int show_journal_by_unit(
                 usec_t not_before,
                 unsigned how_many,
                 bool show_all,
-                bool follow);
+                bool follow,
+                bool warn_cutoff);
 
 const char* output_mode_to_string(OutputMode m);
 OutputMode output_mode_from_string(const char *s);

src/systemctl/systemctl.c

@@ -2554,7 +2554,7 @@ static void print_status_info(UnitStatusInfo *i) {
 
         if (i->id && arg_transport != TRANSPORT_SSH) {
                 printf("\n");
-                show_journal_by_unit(i->id, arg_output, 0, i->inactive_exit_timestamp_monotonic, arg_lines, arg_all, arg_follow);
+                show_journal_by_unit(i->id, arg_output, 0, i->inactive_exit_timestamp_monotonic, arg_lines, arg_all, arg_follow, !arg_quiet);
         }
 
         if (i->need_daemon_reload)

src/systemd/sd-journal.h

@@ -97,6 +97,9 @@ int sd_journal_seek_cursor(sd_journal *j, const char *cursor);
 
 int sd_journal_get_cursor(sd_journal *j, char **cursor);
 
+int sd_journal_get_cutoff_realtime_usec(sd_journal *j, uint64_t *from, uint64_t *to);
+int sd_journal_get_cutoff_monotonic_usec(sd_journal *j, const sd_id128_t boot_id, uint64_t *from, uint64_t *to);
+
 /* int sd_journal_query_unique(sd_journal *j, const char *field);      /\* missing *\/ */
 /* int sd_journal_enumerate_unique(sd_journal *j, const void **data, size_t *l); /\* missing *\/ */
 /* void sd_journal_restart_unique(sd_journal *j);                      /\* missing *\/ */