Re: tail is reading already rotated file.

[Bernhard Voelker]

On 02/04/2015 11:09 AM, 최종우 wrote:
> To reproduce the problem, you can run this script. It exhausted inotify 
> watches. (in order to get the result more
> quickly, decrease the value of max_user_watches.)
> 
> let count=0; echo $count>>a.log; ./tail -F a.log & while true; do mv a.log 
> a.log.$count; let count=count+1; echo
> $count>>a.log; done

The following incomplete quick-shot patch releases the old inotify
resource, and reverts to polling if tail really hits ENOSPC (rather
than a strange "no space left on device" message).
Not tested much - at least it passes the existing tests.
Currently, I've no idea how to test that properly.

I've not looked closer at the other tail bug reported yesterday;
does that interfere with this one?

Have a nice day,
Berny

>From bb6f98c27962d3befb4f9507b87597d3e72b8eac Mon Sep 17 00:00:00 2001
From: Bernhard Voelker <address@hidden>
Date: Thu, 5 Feb 2015 01:40:05 +0100
Subject: [PATCH] tail: avoid inotify resource leaks

* src/tail.c (tail_forever_inotify): When following by name, release
the inotify resource before adding a new one for the file name to
watch.  While at it, diagnose inotify ENOSPC errors more user-friendly
and revert to polling in this case.
---
 src/tail.c | 18 +++++++++++++++---
 1 file changed, 15 insertions(+), 3 deletions(-)

diff --git a/src/tail.c b/src/tail.c
index b512c2a..1cc263a 100644
--- a/src/tail.c
+++ b/src/tail.c
@@ -1571,17 +1571,29 @@ tail_forever_inotify (int wd, struct File_spec *f, 
size_t n_files,
           if (j == n_files)
             continue;

-          /* It's fine to add the same file more than once.  */
+          fspec = &(f[j]);
+
+          /* Remove old watch if following by name.  */
+          if (follow_mode == Follow_name)
+            inotify_rm_watch (wd, fspec->wd);
+
+          /* Add a new watch for the file.  */
           int new_wd = inotify_add_watch (wd, f[j].name, inotify_wd_mask);
           if (new_wd < 0)
             {
+              if (errno == ENOSPC)
+                {
+                  error (0, 0, _("inotify resources exhausted"));
+                  /* Revert to polling.  */
+                  /* FIXME: release hash and inotify resources.  */
+                  errno = 0;
+                  return true;
+                }
               /* Can get ENOENT for a dangling symlink for example.  */
               error (0, errno, _("cannot watch %s"), quote (f[j].name));
               continue;
             }

-          fspec = &(f[j]);
-
           /* Remove 'fspec' and re-add it using 'new_fd' as its key.  */
           hash_delete (wd_to_name, fspec);
           fspec->wd = new_wd;
-- 
2.1.4