journalctl: Improve boot ID lookup

This method should greatly improve offset based lookup, by simply jumping
from one boot to the next boot. It starts at the journal head to get the
a boot ID, makes a _BOOT_ID match and then comes from the opposite
journal direction (tail) to get to the end that boot. After flushing the matches
and advancing the journal from that exact position, we arrive at the start
of next boot. Rinse and repeat.

This is faster than the old method of aggregating the full boot listing just
so we can jump to a specific boot, which can be a real pain on big journals
just for a mere "-b -1" case.

As an additional benefit --list-boots should improve slightly too, because
it does less seeking.

Note that there can be a change in boot order with this lookup method
because it will use the order of boots in the journal, not the realtime stamp
stored in them. That's arguably better, though.
Another deficiency is that it will get confused with boots interleaving in the
journal, therefore, it will refuse operation in --merge, --file and --directory mode.

https://bugs.freedesktop.org/show_bug.cgi?id=72601

1 files changed, 174 insertions, 101 deletions

diff --git a/src/journal/journalctl.c b/src/journal/journalctl.c
index 09f4e0fe38..b51df7d54e 100644
--- a/src/journal/journalctl.c
+++ b/src/journal/journalctl.c
@@ -130,6 +130,7 @@ typedef struct boot_id_t {
         sd_id128_t id;
         uint64_t first;
         uint64_t last;
+        LIST_FIELDS(struct boot_id_t, boot_list);
 } boot_id_t;
 
 static void pager_open_if_enabled(void) {
@@ -734,6 +735,11 @@ static int parse_argv(int argc, char *argv[]) {
                 return -EINVAL;
         }
 
+        if ((arg_boot || arg_action == ACTION_LIST_BOOTS) && (arg_file || arg_directory || arg_merge)) {
+                log_error("Using --boot or --list-boots with --file, --directory or --merge is not supported.");
+                return -EINVAL;
+        }
+
         return 1;
 }
 
@@ -853,111 +859,203 @@ static int add_matches(sd_journal *j, char **args) {
         return 0;
 }
 
-static int boot_id_cmp(const void *a, const void *b) {
-        uint64_t _a, _b;
+static int discover_next_boot(sd_journal *j,
+                              boot_id_t **boot,
+                              bool advance_older,
+                              bool read_realtime) {
+        int r;
+        char match[9+32+1] = "_BOOT_ID=";
+        _cleanup_free_ boot_id_t *next_boot = NULL;
 
-        _a = ((const boot_id_t *)a)->first;
-        _b = ((const boot_id_t *)b)->first;
+        assert(j);
+        assert(boot);
 
-        return _a < _b ? -1 : (_a > _b ? 1 : 0);
-}
+        /* We expect the journal to be on the last position of a boot
+         * (in relation to the direction we are going), so that the next
+         * invocation of sd_journal_next/previous will be from a different
+         * boot. We then collect any information we desire and then jump
+         * to the last location of the new boot by using a _BOOT_ID match
+         * coming from the other journal direction. */
 
-static int get_boots(sd_journal *j,
-                     boot_id_t **boots,
-                     unsigned int *count,
-                     boot_id_t *query_ref_boot) {
-        int r;
-        const void *data;
-        size_t length, allocated = 0;
+        /* Make sure we aren't restricted by any _BOOT_ID matches, so that
+         * we can actually advance to a *different* boot. */
+        sd_journal_flush_matches(j);
 
-        assert(j);
-        assert(boots);
-        assert(count);
+        if (advance_older)
+                r = sd_journal_previous(j);
+        else
+                r = sd_journal_next(j);
+        if (r < 0)
+                return r;
+        else if (r == 0)
+                return 0; /* End of journal, yay. */
+
+        next_boot = new0(boot_id_t, 1);
+        if (!next_boot)
+                return log_oom();
 
-        r = sd_journal_query_unique(j, "_BOOT_ID");
+        r = sd_journal_get_monotonic_usec(j, NULL, &next_boot->id);
         if (r < 0)
                 return r;
 
-        *count = 0;
-        SD_JOURNAL_FOREACH_UNIQUE(j, data, length) {
-                boot_id_t *id;
+        if (read_realtime) {
+                r = sd_journal_get_realtime_usec(j, &next_boot->first);
+                if (r < 0)
+                        return r;
+        }
 
-                assert(startswith(data, "_BOOT_ID="));
+        /* Now seek to the last occurrence of this boot ID. */
+        sd_id128_to_string(next_boot->id, match + 9);
+        r = sd_journal_add_match(j, match, sizeof(match) - 1);
+        if (r < 0)
+                return r;
 
-                if (!GREEDY_REALLOC(*boots, allocated, *count + 1))
-                        return log_oom();
+        if (advance_older)
+                r = sd_journal_seek_head(j);
+        else
+                r = sd_journal_seek_tail(j);
+        if (r < 0)
+                return r;
 
-                id = *boots + *count;
+        if (advance_older)
+                r = sd_journal_next(j);
+        else
+                r = sd_journal_previous(j);
+        if (r < 0)
+                return r;
+        else if (r == 0)
+                return -ENODATA; /* This shouldn't happen. We just came from this very boot ID. */
 
-                r = sd_id128_from_string(((const char *)data) + strlen("_BOOT_ID="), &id->id);
+        if (read_realtime) {
+                r = sd_journal_get_realtime_usec(j, &next_boot->last);
                 if (r < 0)
-                        continue;
+                        return r;
+        }
+
+        *boot = next_boot;
+        next_boot = NULL;
+        return 0;
+}
+
+static int get_boots(sd_journal *j,
+                     boot_id_t **boots,
+                     boot_id_t *query_ref_boot,
+                     int ref_boot_offset) {
+        bool skip_once;
+        int r, count = 0;
+        boot_id_t *head = NULL, *tail = NULL;
+        const bool advance_older = query_ref_boot && ref_boot_offset <= 0;
+
+        assert(j);
+
+        /* Adjust for the asymmetry that offset 0 is
+         * the last (and current) boot, while 1 is considered the
+         * (chronological) first boot in the journal. */
+        skip_once = query_ref_boot && sd_id128_is_null(query_ref_boot->id) && ref_boot_offset < 0;
+
+        /* Advance to the earliest/latest occurrence of our reference
+         * boot ID (taking our lookup direction into account), so that
+         * discover_next_boot() can do its job.
+         * If no reference is given, the journal head/tail will do,
+         * they're "virtual" boots after all. */
+        if (query_ref_boot && !sd_id128_is_null(query_ref_boot->id)) {
+                char match[9+32+1] = "_BOOT_ID=";
 
-                r = sd_journal_add_match(j, data, length);
+                sd_journal_flush_matches(j);
+
+                sd_id128_to_string(query_ref_boot->id, match + 9);
+                r = sd_journal_add_match(j, match, sizeof(match) - 1);
                 if (r < 0)
                         return r;
 
-                r = sd_journal_seek_head(j);
+                if (advance_older)
+                        r = sd_journal_seek_head(j);
+                else
+                        r = sd_journal_seek_tail(j);
                 if (r < 0)
                         return r;
 
-                r = sd_journal_next(j);
+                if (advance_older)
+                        r = sd_journal_next(j);
+                else
+                        r = sd_journal_previous(j);
                 if (r < 0)
                         return r;
                 else if (r == 0)
-                        goto flush;
-
-                r = sd_journal_get_realtime_usec(j, &id->first);
+                        goto finish;
+                else if (ref_boot_offset == 0) {
+                        count = 1;
+                        goto finish;
+                }
+        } else {
+                if (advance_older)
+                        r = sd_journal_seek_tail(j);
+                else
+                        r = sd_journal_seek_head(j);
                 if (r < 0)
                         return r;
 
-                if (query_ref_boot) {
-                        id->last = 0;
-                        if (sd_id128_equal(id->id, query_ref_boot->id))
-                                *query_ref_boot = *id;
-                } else {
-                        r = sd_journal_seek_tail(j);
-                        if (r < 0)
-                                return r;
+                /* No sd_journal_next/previous here. */
+        }
 
-                        r = sd_journal_previous(j);
-                        if (r < 0)
-                                return r;
-                        else if (r == 0)
-                                goto flush;
+        while (true) {
+                _cleanup_free_ boot_id_t *current = NULL;
 
-                        r = sd_journal_get_realtime_usec(j, &id->last);
-                        if (r < 0)
-                                return r;
+                r = discover_next_boot(j, &current, advance_older, !query_ref_boot);
+                if (r < 0) {
+                        boot_id_t *id, *id_next;
+                        LIST_FOREACH_SAFE(boot_list, id, id_next, head)
+                                free(id);
+                        return r;
                 }
 
-                (*count)++;
-        flush:
-                sd_journal_flush_matches(j);
+                if (!current)
+                        break;
+
+                if (query_ref_boot) {
+                        if (!skip_once)
+                                ref_boot_offset += advance_older ? 1 : -1;
+                        skip_once = false;
+
+                        if (ref_boot_offset == 0) {
+                                count = 1;
+                                query_ref_boot->id = current->id;
+                                break;
+                        }
+                } else {
+                        LIST_INSERT_AFTER(boot_list, head, tail, current);
+                        tail = current;
+                        current = NULL;
+                        count++;
+                }
         }
 
-        qsort_safe(*boots, *count, sizeof(boot_id_t), boot_id_cmp);
-        return 0;
+finish:
+        if (boots)
+                *boots = head;
+
+        sd_journal_flush_matches(j);
+
+        return count;
 }
 
 static int list_boots(sd_journal *j) {
-        int r, w, i;
-        unsigned int count;
-        boot_id_t *id;
-        _cleanup_free_ boot_id_t *all_ids = NULL;
+        int w, i, count;
+        boot_id_t *id, *id_next, *all_ids;
 
         assert(j);
 
-        r = get_boots(j, &all_ids, &count, NULL);
-        if (r < 0)
-                return r;
+        count = get_boots(j, &all_ids, NULL, 0);
+        if (count <= 0)
+                return count;
 
         pager_open_if_enabled();
 
         /* numbers are one less, but we need an extra char for the sign */
         w = DECIMAL_STR_WIDTH(count - 1) + 1;
 
-        for (id = all_ids, i = 0; id < all_ids + count; id++, i++) {
+        i = 0;
+        LIST_FOREACH_SAFE(boot_list, id, id_next, all_ids) {
                 char a[FORMAT_TIMESTAMP_MAX], b[FORMAT_TIMESTAMP_MAX];
 
                 printf("% *i " SD_ID128_FORMAT_STR " %s—%s\n",
@@ -965,39 +1063,8 @@ static int list_boots(sd_journal *j) {
                        SD_ID128_FORMAT_VAL(id->id),
                        format_timestamp_maybe_utc(a, sizeof(a), id->first),
                        format_timestamp_maybe_utc(b, sizeof(b), id->last));
-        }
-
-        return 0;
-}
-
-static int get_boot_id_by_offset(sd_journal *j, sd_id128_t *boot_id, int offset) {
-        int r;
-        unsigned int count;
-        boot_id_t ref_boot_id = {}, *id;
-        _cleanup_free_ boot_id_t *all_ids = NULL;
-
-        assert(j);
-        assert(boot_id);
-
-        ref_boot_id.id = *boot_id;
-        r = get_boots(j, &all_ids, &count, &ref_boot_id);
-        if (r < 0)
-                return r;
-
-        if (sd_id128_equal(*boot_id, SD_ID128_NULL)) {
-                if (offset > (int) count || offset <= -(int)count)
-                        return -EADDRNOTAVAIL;
-
-                *boot_id = all_ids[(offset <= 0)*count + offset - 1].id;
-        } else {
-                id = bsearch(&ref_boot_id, all_ids, count, sizeof(boot_id_t), boot_id_cmp);
-
-                if (!id ||
-                    offset <= 0 ? (id - all_ids) + offset < 0 :
-                                    (id - all_ids) + offset >= (int) count)
-                        return -EADDRNOTAVAIL;
-
-                *boot_id = (id + offset)->id;
+                i++;
+                free(id);
         }
 
         return 0;
@@ -1006,6 +1073,7 @@ static int get_boot_id_by_offset(sd_journal *j, sd_id128_t *boot_id, int offset)
 static int add_boot(sd_journal *j) {
         char match[9+32+1] = "_BOOT_ID=";
         int r;
+        boot_id_t ref_boot_id = {};
 
         assert(j);
 
@@ -1015,17 +1083,22 @@ static int add_boot(sd_journal *j) {
         if (arg_boot_offset == 0 && sd_id128_equal(arg_boot_id, SD_ID128_NULL))
                 return add_match_this_boot(j, arg_machine);
 
-        r = get_boot_id_by_offset(j, &arg_boot_id, arg_boot_offset);
-        if (r < 0) {
-                if (sd_id128_equal(arg_boot_id, SD_ID128_NULL))
-                        log_error_errno(r, "Failed to look up boot %+i: %m", arg_boot_offset);
+        ref_boot_id.id = arg_boot_id;
+        r = get_boots(j, NULL, &ref_boot_id, arg_boot_offset);
+        assert(r <= 1);
+        if (r <= 0) {
+                const char *reason = (r == 0) ? "No such boot ID in journal" : strerror(-r);
+
+                if (sd_id128_is_null(arg_boot_id))
+                        log_error("Failed to look up boot %+i: %s", arg_boot_offset, reason);
                 else
                         log_error("Failed to look up boot ID "SD_ID128_FORMAT_STR"%+i: %s",
-                                  SD_ID128_FORMAT_VAL(arg_boot_id), arg_boot_offset, strerror(-r));
-                return r;
+                                  SD_ID128_FORMAT_VAL(arg_boot_id), arg_boot_offset, reason);
+
+                return r == 0 ? -ENODATA : r;
         }
 
-        sd_id128_to_string(arg_boot_id, match + 9);
+        sd_id128_to_string(ref_boot_id.id, match + 9);
 
         r = sd_journal_add_match(j, match, sizeof(match) - 1);
         if (r < 0)