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From cc5710c3ad0ff51fa84b736d66d5f70aa0ade2b3 Mon Sep 17 00:00:00 2001
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From: Lennart Poettering <lennart@poettering.net>
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Date: Mon, 25 Apr 2016 18:08:42 +0200
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Subject: [PATCH] journalctl: don't trust the per-field entry tables when
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 looking for boot IDs
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When appending to a journal file, journald will:
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a) first, append the actual entry to the end of the journal file
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b) second, add an offset reference to it to the global entry array stored at
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   the beginning of the file
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c) third, add offset references to it to the per-field entry array stored at
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   various places of the file
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The global entry array, maintained by b) is used when iterating through the
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journal without matches applied.
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The per-field entry array maintained by c) is used when iterating through the
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journal with a match for that specific field applied.
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In the wild, there are journal files where a) and b) were completed, but c)
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was not before the files were abandoned. This means, that in some cases log
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entries are at the end of these files that appear in the global entry array,
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but not in the per-field entry array of the _BOOT_ID= field. Now, the
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"journalctl --list-boots" command alternatingly uses the global entry array
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and the per-field entry array of the _BOOT_ID= field. It seeks to the last
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entry of a specific _BOOT_ID=field by having the right match installed, and
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then jumps to the next following entry with no match installed anymore, under
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the assumption this would bring it to the next boot ID. However, if the
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per-field entry wasn't written fully, it might actually turn out that the
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global entry array might know one more entry with the same _BOOT_ID, thus
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resulting in a indefinite loop around the same _BOOT_ID.
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This patch fixes that, by updating the boot search logic to always continue
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reading entries until the boot ID actually changed from the previous. Thus, the
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per-field entry array is used as quick jump index (i.e. as an optimization),
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but not trusted otherwise.  Only the global entry array is trusted.
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This replaces PR #1904, which is actually very similar to this one. However,
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this one actually reads the boot ID directly from the entry header, and doesn't
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try to read it at all until the read pointer is actually really located on the
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first item to read.
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Fixes: #617
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Replaces: #1904
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Cherry-picked from: dc00966228ff90c554fd034e588ea55eb605ec52
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Related: #1318994
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---
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 src/journal/journalctl.c | 71 ++++++++++++++++++++++++----------------
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 1 file changed, 42 insertions(+), 29 deletions(-)
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diff --git a/src/journal/journalctl.c b/src/journal/journalctl.c
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index 5864ff50a6..723854a2e9 100644
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--- a/src/journal/journalctl.c
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+++ b/src/journal/journalctl.c
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@@ -941,18 +941,18 @@ static void boot_id_free_all(BootId *l) {
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         }
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 }
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-static int discover_next_boot(
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-                sd_journal *j,
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-                BootId **boot,
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+static int discover_next_boot(sd_journal *j,
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+                sd_id128_t previous_boot_id,
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                 bool advance_older,
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-                bool read_realtime) {
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+                BootId **ret) {
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-        int r;
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-        char match[9+32+1] = "_BOOT_ID=";
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         _cleanup_free_ BootId *next_boot = NULL;
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+        char match[9+32+1] = "_BOOT_ID=";
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+        sd_id128_t boot_id;
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+        int r;
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         assert(j);
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-        assert(boot);
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+        assert(ret);
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         /* We expect the journal to be on the last position of a boot
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          * (in relation to the direction we are going), so that the next
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@@ -965,29 +965,40 @@ static int discover_next_boot(
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          * we can actually advance to a *different* boot. */
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         sd_journal_flush_matches(j);
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-        if (advance_older)
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-                r = sd_journal_previous(j);
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-        else
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-                r = sd_journal_next(j);
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-        if (r < 0)
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-                return r;
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-        else if (r == 0)
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-                return 0; /* End of journal, yay. */
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+        do {
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+                if (advance_older)
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+                        r = sd_journal_previous(j);
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+                else
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+                        r = sd_journal_next(j);
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+                if (r < 0)
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+                        return r;
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+                else if (r == 0)
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+                        return 0; /* End of journal, yay. */
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+
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+                r = sd_journal_get_monotonic_usec(j, NULL, &boot_id);
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+                if (r < 0)
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+                        return r;
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+
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+                /* We iterate through this in a loop, until the boot ID differs from the previous one. Note that
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+                 * normally, this will only require a single iteration, as we seeked to the last entry of the previous
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+                 * boot entry already. However, it might happen that the per-journal-field entry arrays are less
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+                 * complete than the main entry array, and hence might reference an entry that's not actually the last
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+                 * one of the boot ID as last one. Let's hence use the per-field array is initial seek position to
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+                 * speed things up, but let's not trust that it is complete, and hence, manually advance as
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+                 * necessary. */
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+
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+        } while (sd_id128_equal(boot_id, previous_boot_id));
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         next_boot = new0(BootId, 1);
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         if (!next_boot)
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                 return log_oom();
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-        r = sd_journal_get_monotonic_usec(j, NULL, &next_boot->id);
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+        next_boot->id = boot_id;
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+
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+        r = sd_journal_get_realtime_usec(j, &next_boot->first);
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         if (r < 0)
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                 return r;
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-        if (read_realtime) {
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-                r = sd_journal_get_realtime_usec(j, &next_boot->first);
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-                if (r < 0)
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-                        return r;
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-        }
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-
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         /* Now seek to the last occurrence of this boot ID. */
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         sd_id128_to_string(next_boot->id, match + 9);
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         r = sd_journal_add_match(j, match, sizeof(match) - 1);
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@@ -1010,13 +1021,11 @@ static int discover_next_boot(
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         else if (r == 0)
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                 return -ENODATA; /* This shouldn't happen. We just came from this very boot ID. */
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-        if (read_realtime) {
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-                r = sd_journal_get_realtime_usec(j, &next_boot->last);
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-                if (r < 0)
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-                        return r;
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-        }
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+        r = sd_journal_get_realtime_usec(j, &next_boot->last);
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+        if (r < 0)
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+                return r;
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-        *boot = next_boot;
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+        *ret = next_boot;
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         next_boot = NULL;
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         return 0;
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@@ -1032,6 +1041,7 @@ static int get_boots(
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         int r, count = 0;
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         BootId *head = NULL, *tail = NULL;
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         const bool advance_older = query_ref_boot && ref_boot_offset <= 0;
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+        sd_id128_t previous_boot_id;
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         assert(j);
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@@ -1085,10 +1095,11 @@ static int get_boots(
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                 /* No sd_journal_next/previous here. */
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         }
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+        previous_boot_id = SD_ID128_NULL;
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         for (;;) {
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                 _cleanup_free_ BootId *current = NULL;
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-                r = discover_next_boot(j, &current, advance_older, !query_ref_boot);
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+                r = discover_next_boot(j, previous_boot_id, advance_older, ¤t;;
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                 if (r < 0) {
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                         boot_id_free_all(head);
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                         return r;
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@@ -1097,6 +1108,8 @@ static int get_boots(
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                 if (!current)
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                         break;
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+                previous_boot_id = current->id;
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+
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                 if (query_ref_boot) {
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                         if (!skip_once)
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                                 ref_boot_offset += advance_older ? 1 : -1;