GNU bug report logs - #19760
[bug] "tail -f" with inotify fails to follow a file after a rename()

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From: Pádraig Brady <P <at> draigBrady.com>
To: Stephane Chazelas <stephane.chazelas <at> gmail.com>,  19760 <at> debbugs.gnu.org
Subject: bug#19760: [bug] "tail -f" with inotify fails to follow a file after a rename()
Date: Tue, 03 Feb 2015 23:30:34 +0000

On 03/02/15 22:04, Stephane Chazelas wrote:
> Hello,
> 
> On Linux, when inotify is used,
> 
>    tail -f file
> 
> follows a file only until it's renamed. After it is renamed, the
> inotify watch is removed, which means tail sits there doing
> nothing and any further modifications to the file are ignored.
> 
> To reproduce:
> 
>     echo 1 > file
>     tail -f file &
>     exec 3>> file
>     echo 2 >&3
>     sleep 1
>     mv file file2
>     sleep 1
>     echo 3 >&3
>     sleep 1
>     : > file2
> 
> "3" is not displayed. No message about the file being truncated
> either.
> 
> Work arounds:
> 
>    tail ---disable-inotify -f file
>    tail -f < file # effectively disables inotify
> 
>    or rename the file with a link() followed by an unlink()
>    ln file newfile && rm -f file
> 
> Note that the IN_DELETED_SELF event is not reached in
> follow-descriptor mode because tail has the file open preventing
> it from being deleted even after it's unlinked from the last
> directory.
> 
> Patch attached (on the current git head).

Ouch. The patch makes sense on first glance,
and all existing tests pass with it.
I'll check some more and add a test.

thanks!
Pádraig.

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