Assaf Gordon <assafgordon@HIDDEN>
to control <at> debbugs.gnu.org.
Full text available.Received: (at 19765) by debbugs.gnu.org; 5 Feb 2015 13:07:58 +0000 From debbugs-submit-bounces <at> debbugs.gnu.org Thu Feb 05 08:07:58 2015 Received: from localhost ([127.0.0.1]:34583 helo=debbugs.gnu.org) by debbugs.gnu.org with esmtp (Exim 4.80) (envelope-from <debbugs-submit-bounces <at> debbugs.gnu.org>) id 1YJMA1-00068H-NS for submit <at> debbugs.gnu.org; Thu, 05 Feb 2015 08:07:58 -0500 Received: from mail2.vodafone.ie ([213.233.128.44]:59413) by debbugs.gnu.org with esmtp (Exim 4.80) (envelope-from <P@HIDDEN>) id 1YJM9y-000681-RI for 19765 <at> debbugs.gnu.org; Thu, 05 Feb 2015 08:07:55 -0500 X-IronPort-Anti-Spam-Filtered: true X-IronPort-Anti-Spam-Result: AmoFAChq01RtTD0E/2dsb2JhbABagwaDXU/CbYJPAoElQwEBAQEBfYQNAQUjDwFWCw0LAgIFFgsCAgkDAgECAUUGAQwIAQGILQG/U4VpkEkBCyCBIY5egmiBQQWZVYEhhB0LjAoig24+gnMBAQE Received: from unknown (HELO localhost.localdomain) ([109.76.61.4]) by mail2.vodafone.ie with ESMTP; 05 Feb 2015 13:07:47 +0000 Message-ID: <54D36B22.6080803@HIDDEN> Date: Thu, 05 Feb 2015 13:07:46 +0000 From: =?UTF-8?B?UMOhZHJhaWcgQnJhZHk=?= <P@HIDDEN> User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.4.0 MIME-Version: 1.0 To: Stephane Chazelas <stephane.chazelas@HIDDEN>, 19765 <at> debbugs.gnu.org Subject: Re: bug#19765: tail -F stops watching when read permissions are removed References: <20150204102211.GB6648@HIDDEN> In-Reply-To: <20150204102211.GB6648@HIDDEN> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit X-Spam-Score: 0.0 (/) X-Debbugs-Envelope-To: 19765 X-BeenThere: debbugs-submit <at> debbugs.gnu.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: <debbugs-submit.debbugs.gnu.org> List-Unsubscribe: <https://debbugs.gnu.org/cgi-bin/mailman/options/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=unsubscribe> List-Archive: <https://debbugs.gnu.org/cgi-bin/mailman/private/debbugs-submit/> List-Post: <mailto:debbugs-submit <at> debbugs.gnu.org> List-Help: <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=help> List-Subscribe: <https://debbugs.gnu.org/cgi-bin/mailman/listinfo/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=subscribe> Errors-To: debbugs-submit-bounces <at> debbugs.gnu.org Sender: "Debbugs-submit" <debbugs-submit-bounces <at> debbugs.gnu.org> X-Spam-Score: 0.0 (/) On 04/02/15 10:22, Stephane Chazelas wrote: > When watchnig a file by name with "tail -F", if read permissions > are removed, tail stops watching even though it has a file > descriptor open on the file. > > With inotify: > > $ : > file > $ tail -F file & > [1] 20796 > $ exec 3>> file > $ echo 1 >&3 > 1 > $ chmod 0 file > tail: % cannot watch ‘file’: Permission denied > tail: ‘file’ has become inaccessible: Permission denied > $ echo 2 >&3 ## not detected at this point > $ chmod +r file > tail: ‘file’ has become accessible > # new content not displayed yet. > $ echo 3 >&3 > 1 ## all lines displayed > 2 > 3 > > Without inotify: > > $ : > file > $ tail -F ---disable-inotify file & > [1] 20903 > $ exec 3>> file > $ echo 1 >&3 > 1 > $ chmod 0 file > $ echo 2 >&3 > 2 # not detected yet > $ tail: ‘file’ has become inaccessible: Permission denied > > $ echo 3 >&3 > $ chmod +r file > $ tail: ‘file’ has become accessible > 1 > 2 > 3 > > (same except there's a delay before tail detects the file is no longer > readable). > > Note that the file in that case is still accessible, one can > still do a stat() on it to check that the file is still the same > one. That's different from when one of the directory components > becomes unreadable/unsearchable, in which case tail can't tell > if it's still reading the right file as in: > > tail -F foo/bar & > chmod 0 foo > > There, tail still has an open file descriptor to foo/bar, but > can't tell if it still points to the "foo/bar" file, so it's > acceptable for it to stop watching in that case. > > With inotify though, it doesn't unless the file attributes are > changed (chmod...) or the file is renamed. I think I'll raise a > separate bug report for that and directory components being > renamed. > > [tested with git head] > Handling of files that only change perms is awkward. In the inotify case we don't close the associated watch descriptor so continue to process events, though ignore them as we've closed the file. Another problem in this situation with inotify is that write events between the chmod a-r and a+r are lost, thus not outputting new data until the next write event. Another larger problem in this situation with and without inotify is that the whole file is output, when tail outputs next. That's documented as a FIXME-maybe in the code. thanks, Pádraig.
bug-coreutils@HIDDEN:bug#19765; Package coreutils.
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[94.195.59.201]) by mx.google.com with ESMTPSA id eb10sm2539515wib.13.2015.02.04.02.22.12 for <bug-coreutils@HIDDEN> (version=TLSv1.2 cipher=RC4-SHA bits=128/128); Wed, 04 Feb 2015 02:22:12 -0800 (PST) Date: Wed, 4 Feb 2015 10:22:11 +0000 From: Stephane Chazelas <stephane.chazelas@HIDDEN> To: bug-coreutils@HIDDEN Subject: tail -F stops watching when read permissions are removed Message-ID: <20150204102211.GB6648@HIDDEN> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit User-Agent: Mutt/1.5.21 (2010-09-15) X-detected-operating-system: by eggs.gnu.org: Error: Malformed IPv6 address (bad octet value). X-detected-operating-system: by eggs.gnu.org: Error: Malformed IPv6 address (bad octet value). X-Received-From: 2001:4830:134:3::11 X-Spam-Score: -4.0 (----) X-Debbugs-Envelope-To: submit X-BeenThere: debbugs-submit <at> debbugs.gnu.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: <debbugs-submit.debbugs.gnu.org> List-Unsubscribe: <https://debbugs.gnu.org/cgi-bin/mailman/options/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=unsubscribe> List-Archive: <https://debbugs.gnu.org/cgi-bin/mailman/private/debbugs-submit/> List-Post: <mailto:debbugs-submit <at> debbugs.gnu.org> List-Help: <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=help> List-Subscribe: <https://debbugs.gnu.org/cgi-bin/mailman/listinfo/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=subscribe> Errors-To: debbugs-submit-bounces <at> debbugs.gnu.org Sender: "Debbugs-submit" <debbugs-submit-bounces <at> debbugs.gnu.org> X-Spam-Score: -4.0 (----) When watchnig a file by name with "tail -F", if read permissions are removed, tail stops watching even though it has a file descriptor open on the file. With inotify: $ : > file $ tail -F file & [1] 20796 $ exec 3>> file $ echo 1 >&3 1 $ chmod 0 file tail: % cannot watch ‘file’: Permission denied tail: ‘file’ has become inaccessible: Permission denied $ echo 2 >&3 ## not detected at this point $ chmod +r file tail: ‘file’ has become accessible # new content not displayed yet. $ echo 3 >&3 1 ## all lines displayed 2 3 Without inotify: $ : > file $ tail -F ---disable-inotify file & [1] 20903 $ exec 3>> file $ echo 1 >&3 1 $ chmod 0 file $ echo 2 >&3 2 # not detected yet $ tail: ‘file’ has become inaccessible: Permission denied $ echo 3 >&3 $ chmod +r file $ tail: ‘file’ has become accessible 1 2 3 (same except there's a delay before tail detects the file is no longer readable). Note that the file in that case is still accessible, one can still do a stat() on it to check that the file is still the same one. That's different from when one of the directory components becomes unreadable/unsearchable, in which case tail can't tell if it's still reading the right file as in: tail -F foo/bar & chmod 0 foo There, tail still has an open file descriptor to foo/bar, but can't tell if it still points to the "foo/bar" file, so it's acceptable for it to stop watching in that case. With inotify though, it doesn't unless the file attributes are changed (chmod...) or the file is renamed. I think I'll raise a separate bug report for that and directory components being renamed. [tested with git head] -- Stephane
Stephane Chazelas <stephane.chazelas@HIDDEN>:bug-coreutils@HIDDEN.
Full text available.bug-coreutils@HIDDEN:bug#19765; Package coreutils.
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