From 1ed5aa2254505fbf971c6db6810130227f552eec Mon Sep 17 00:00:00 2001
From: root <root@localhost.localdomain>
Date: Thu, 16 May 2024 10:57:26 +0800
Subject: [PATCH] tac: handle short reads on input

This can be reproduced by getting the read() above 2G,
which induces a short read, thus triggering the erroneous failure.

  $ truncate -s 5G 5G

  $ cat 5G | TMPDIR=$PWD tac | wc -c
  tac: /tmp/tacFt7txA: read error: Illegal seek
  0

With the fix in place we now get:

  $ cat 5G | TMPDIR=$PWD src/tac | wc -c
  5368709120
---
 NEWS      | 5 +++++
 src/tac.c | 3 ++-
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/NEWS b/NEWS
index 4a09ab4..39d1024 100644
--- a/NEWS
+++ b/NEWS
@@ -207,6 +207,11 @@ GNU coreutils NEWS                                    -*- outline -*-
   non regular files are specified, as inotify is ineffective with these.
   [bug introduced with inotify support added in coreutils-7.5]
 
+  tac now handles short reads on its input.  Previously it may have exited
+  erroneously, especially with large input files with no separators.
+  [This bug was present in "the beginning".]
+
+
   uptime no longer outputs the AM/PM component of the current time,
   as that's inconsistent with the 24 hour time format used.
   [bug introduced in coreutils-7.0]
diff --git a/src/tac.c b/src/tac.c
index 753f8f1..1186d94 100644
--- a/src/tac.c
+++ b/src/tac.c
@@ -46,6 +46,7 @@ tac -r -s '.\|
 #include "die.h"
 #include "error.h"
 #include "filenamecat.h"
+#include "full-read.h"
 #include "safe-read.h"
 #include "stdlib--.h"
 #include "xbinary-io.h"
@@ -352,7 +353,7 @@ tac_seekable (int input_fd, const char *file, off_t file_pos)
           else
             match_start = past_end;
 
-          if (safe_read (input_fd, G_buffer, read_size) != read_size)
+          if (full_read (input_fd, G_buffer, read_size) != read_size)
             {
               error (0, errno, _("%s: read error"), quotef (file));
               return false;
-- 
2.39.3