From: Pádraig Brady <P@draigBrady.com>
Date: Mon, 30 Jan 2023 21:44:10 +0000 (+0000)
Subject: tail: fix support for -F with non seekable files
X-Git-Tag: v9.2~64
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=c0c63e9735908a9579f8735001957db6bd81afc3;p=thirdparty%2Fcoreutils.git

tail: fix support for -F with non seekable files

This was seen to be an issue when following a
symlink that was being updated to point to
different underlying devices.

* src/tail.c (recheck): Guard the lseek() call to only
be performed for regular files.
* NEWS: Mention the bug fix.
---

diff --git a/NEWS b/NEWS
index 27334a595c..eb8380e117 100644
--- a/NEWS
+++ b/NEWS
@@ -52,6 +52,10 @@ GNU coreutils NEWS                                    -*- outline -*-
   Previously it may have output 1 character too wide for certain widths.
   [bug introduced in coreutils-5.3]
 
+  tail --follow=name works again with non seekable files.  Previously it
+  exited with an "Illegal seek" error when such a file was replaced.
+  [bug introduced in fileutils-4.1.6]
+
   `wc -c` will again efficiently determine the size of large files
   on all systems.  It no longer redundantly reads data from certain
   sized files larger than SIZE_MAX.
diff --git a/src/tail.c b/src/tail.c
index 2244509dd7..03061e8bf7 100644
--- a/src/tail.c
+++ b/src/tail.c
@@ -1122,7 +1122,8 @@ recheck (struct File_spec *f, bool blocking)
     {
       /* Start at the beginning of the file.  */
       record_open_fd (f, fd, 0, &new_stats, (is_stdin ? -1 : blocking));
-      xlseek (fd, 0, SEEK_SET, pretty_name (f));
+      if (S_ISREG (new_stats.st_mode))
+        xlseek (fd, 0, SEEK_SET, pretty_name (f));
     }
 }