GNU bug report logs - #16669
rm: inconsistent 'rm -ir' prompting behavior (POSIX issue)

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Eric Blake <eblake <at> redhat.com>
To: bug-coreutils <at> gnu.org
Subject: inconsistent 'rm -ir' prompting behavior
Date: Thu, 06 Feb 2014 09:39:10 -0700

[Message part 1 (text/plain, inline)]

On today's Austin Group call, we discussed
http://austingroupbugs.net/view.php?id=802 regarding 'rm' behavior.

They pointed out that GNU has an optimization not allowed by a strict
reading of the current standard:

$ mkdir foo
$ rm -ir foo
rm: remove directory ‘foo’?

Whether you answer yes or no, the point remains: rm only prompted once
about removing the empty directory.  Compare that to other
implementations, such as Solaris:

$ rm -ir /tmp/foo
rm: examine files in directory /tmp/foo (yes/no)? y
rm: remove /tmp/foo (yes/no)? y
$

Note that the optimization implies that we did a readdir() on the
directory before deciding whether to prompt, in order to learn if it was
empty; and that readdir() modifies directory atime; in the Solaris
implementation, readdir() is not even attempted until after a positive
prompt response, which means directory atime is unchanged if the user
chooses not to descend.

Meanwhile, for a non-empty directory, we DO prompt twice for the directory:

$ touch foo/bar
$ rm -ir foo
rm: descend into directory ‘foo’? y
rm: remove regular empty file ‘foo/bar’? y
rm: remove directory ‘foo’?

Here, we get the POSIX-mandated double prompting, once to descend, and
once after recursion is complete to see whether to remove the now-empty
directory.  The argument is whether the GNU optimization of prompting
only once for an empty directory violates POSIX (and where it is
observable by a new directory atime), or whether we should patch POSIX
to allow the GNU optimization.  In the meeting, I ended up with an
action item to right the bug report against POSIX to propose wording
that would allow the GNU behavior.

Conversely, consider:

$ rm -ir foo
rm: descend into directory ‘foo’? y
rm: remove regular empty file ‘foo/bar’? n
rm: remove directory ‘foo’? y
rm: cannot remove ‘foo’: Directory not empty

Why on earth are we prompting to remove 'foo' when we KNOW it is
non-empty because the user specifically asked to not remove foo/bar?  If
we can optimize from two prompts down to one for the empty directory
case, why are we not optimizing and avoiding asking a useless prompt for
a known non-empty directory?  So, while writing my POSIX bug report,
should I also allow for an optimization of omitting the second prompt
for a known non-empty directory (known because of a negative answer to
prompts on its children), even though GNU does not yet implement that
optimization?

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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Message #8 received at 16669 <at> debbugs.gnu.org (full text, mbox):

From: Paul Eggert <eggert <at> cs.ucla.edu>
To: Eric Blake <eblake <at> redhat.com>, 16669 <at> debbugs.gnu.org
Subject: Re: bug#16669: inconsistent 'rm -ir' prompting behavior
Date: Thu, 06 Feb 2014 09:03:50 -0800

On 02/06/2014 08:39 AM, Eric Blake wrote:
> should I also allow for an optimization of omitting the second prompt
> for a known non-empty directory

I would, yes.  Thanks for catching that.

> (known because of a negative answer to
> prompts on its children)
It might also be known because of a failed attempt to remove a child, 
and this optimization should be allowed as well.

Message #11 received at 16669 <at> debbugs.gnu.org (full text, mbox):

From: Eric Blake <eblake <at> redhat.com>
To: Paul Eggert <eggert <at> cs.ucla.edu>, 16669 <at> debbugs.gnu.org
Subject: Re: bug#16669: inconsistent 'rm -ir' prompting behavior
Date: Thu, 06 Feb 2014 10:33:35 -0700

[Message part 1 (text/plain, inline)]

On 02/06/2014 10:03 AM, Paul Eggert wrote:
> On 02/06/2014 08:39 AM, Eric Blake wrote:
>> should I also allow for an optimization of omitting the second prompt
>> for a known non-empty directory
> 
> I would, yes.  Thanks for catching that.
> 
>> (known because of a negative answer to
>> prompts on its children)
> It might also be known because of a failed attempt to remove a child,
> and this optimization should be allowed as well.

http://austingroupbugs.net/view.php?id=819 was created to attempt this,
although it may need another round of word-smithing to make sure it is
correct for what we want.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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Message #14 received at 16669 <at> debbugs.gnu.org (full text, mbox):

From: Pádraig Brady <P <at> draigBrady.com>
To: Eric Blake <eblake <at> redhat.com>
Cc: 16669 <at> debbugs.gnu.org
Subject: Re: bug#16669: inconsistent 'rm -ir' prompting behavior
Date: Thu, 06 Feb 2014 17:44:11 +0000

On 02/06/2014 04:39 PM, Eric Blake wrote:
> On today's Austin Group call, we discussed
> http://austingroupbugs.net/view.php?id=802 regarding 'rm' behavior.
> 
> They pointed out that GNU has an optimization not allowed by a strict
> reading of the current standard:
> 
> $ mkdir foo
> $ rm -ir foo
> rm: remove directory ‘foo’?
> 
> Whether you answer yes or no, the point remains: rm only prompted once
> about removing the empty directory

[snip]

> Conversely, consider:
> 
> $ rm -ir foo
> rm: descend into directory ‘foo’? y
> rm: remove regular empty file ‘foo/bar’? n
> rm: remove directory ‘foo’? y
> rm: cannot remove ‘foo’: Directory not empty
> 
> Why on earth are we prompting to remove 'foo' when we KNOW it is
> non-empty because the user specifically asked to not remove foo/bar?  If
> we can optimize from two prompts down to one for the empty directory
> case, why are we not optimizing and avoiding asking a useless prompt for
> a known non-empty directory?

The different handling could be useful I think.

When we determine there are no files in a dir,
then only one prompt is necessary.

If we determine files are present a separate prompt
is useful to cater for the following sequence
in terminal 1 and terminal 2.

1> $ rm -ir foo
1> rm: descend into directory ‘foo’? y
1> rm: remove regular empty file ‘foo/bar’? n
1> rm: remove directory ‘foo’?

2> mv foo/bar /safe/foo  # Handle this unknown file _independently_

1> y

thanks,
Pádraig.

Message #17 received at 16669 <at> debbugs.gnu.org (full text, mbox):

From: Assaf Gordon <assafgordon <at> gmail.com>
To: Pádraig Brady <P <at> draigBrady.com>,
 Eric Blake <eblake <at> redhat.com>
Cc: 16669 <at> debbugs.gnu.org
Subject: Re: bug#16669: inconsistent 'rm -ir' prompting behavior
Date: Fri, 19 Oct 2018 17:34:08 -0600

(triaging old bugs)

Eric, Pádraig,

On 06/02/14 10:44 AM, Pádraig Brady wrote:
> On 02/06/2014 04:39 PM, Eric Blake wrote:
>> On today's Austin Group call, we discussed
>> http://austingroupbugs.net/view.php?id=802 regarding 'rm' behavior.
>>

Was there ever a resolution (or a committed fix)
for the "rm -ir" issue in:
  https://bugs.gnu.org/16669


-assaf

Message #20 received at 16669 <at> debbugs.gnu.org (full text, mbox):

From: Paul Eggert <eggert <at> cs.ucla.edu>
To: Assaf Gordon <assafgordon <at> gmail.com>, Pádraig Brady
 <P <at> draigBrady.com>, Eric Blake <eblake <at> redhat.com>
Cc: 16669 <at> debbugs.gnu.org
Subject: Re: bug#16669: inconsistent 'rm -ir' prompting behavior
Date: Sat, 20 Oct 2018 17:08:23 -0700

Assaf Gordon wrote:
> Was there ever a resolution (or a committed fix)
> for the "rm -ir" issue in:
> https://bugs.gnu.org/16669

Not yet. I'd leave the bug open.

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