From c4cdbb978f681e7356c6c6367c1730d156a6a4e0 Mon Sep 17 00:00:00 2001
From: Mike Yuan <me@yhndnzj.com>
Date: Sat, 18 Feb 2023 21:49:21 +0800
Subject: [PATCH] journalctl: fix output when --lines is used with --grep

Previously, we skip the entries before arg_lines
unconditionally, which doesn't behave correctly
when used with --grep. After this commit, when
a pattern is specified, we don't skip the entries
early, but rely on the count of the lines shown
to tell us when to stop. To achieve that we would
have to search backwards instead.

Fixes #25147

(cherry picked from commit db4691961ca52759fe6645d0fddb659ee4299ac2)
---
 man/journalctl.xml       | 8 ++++++--
 src/journal/journalctl.c | 5 +++++
 2 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/man/journalctl.xml b/man/journalctl.xml
index 109797776e..ae86c50d62 100644
--- a/man/journalctl.xml
+++ b/man/journalctl.xml
@@ -363,7 +363,9 @@
 
         <para>If the pattern is all lowercase, matching is case insensitive.  Otherwise, matching is case
         sensitive. This can be overridden with the <option>--case-sensitive</option> option, see
-        below.</para></listitem>
+        below.</para>
+
+        <para>When used with <option>--lines=</option>, <option>--reverse</option> is implied.</para></listitem>
       </varlistentry>
 
       <varlistentry>
@@ -540,7 +542,9 @@
         <listitem><para>Show the most recent journal events and limit the number of events shown. If
         <option>--follow</option> is used, this option is implied. The argument is a positive integer or
         <literal>all</literal> to disable line limiting. The default value is 10 if no argument is
-        given.</para></listitem>
+        given.</para>
+
+        <para>When used with <option>--grep=</option>, <option>--reverse</option> is implied.</para></listitem>
       </varlistentry>
 
       <varlistentry>
diff --git a/src/journal/journalctl.c b/src/journal/journalctl.c
index b2883ff177..da0fac548e 100644
--- a/src/journal/journalctl.c
+++ b/src/journal/journalctl.c
@@ -1083,6 +1083,11 @@ static int parse_argv(int argc, char *argv[]) {
                 r = pattern_compile_and_log(arg_pattern, arg_case, &arg_compiled_pattern);
                 if (r < 0)
                         return r;
+
+                /* When --grep is used along with --lines, we don't know how many lines we can print.
+                 * So we search backwards and count until enough lines have been printed or we hit the head. */
+                if (arg_lines >= 0)
+                        arg_reverse = true;
         }
 
         return 1;