GNU bug report logs - #3911
get-free-disk-space race condition on default-directory test

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From: help-debbugs <at> gnu.org (Emacs bug Tracking System)
To: Kevin Ryde <user42 <at> zip.com.au>
Subject: bug#3911 closed by Chong Yidong <cyd <at> stupidchicken.com> (Re:
 get-free-disk-space when default-directory doesn't exist)
Date: Sun, 16 Aug 2009 00:40:17 +0000

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

This is an automatic notification regarding your bug report
which was filed against the emacs package:

#3911: 23.1.50; get-free-disk-space relative to non-existent default-directory

It has been closed by Chong Yidong <cyd <at> stupidchicken.com>.

Their explanation is attached below along with your original report.
If this explanation is unsatisfactory and you have not received a
better one in a separate message then please contact Chong Yidong <cyd <at> stupidchicken.com> by
replying to this email.


-- 
3911: http://debbugs.gnu.org/cgi/bugreport.cgi?bug=3911
Emacs Bug Tracking System
Contact help-debbugs <at> gnu.org with problems

[Message part 2 (message/rfc822, inline)]

From: Chong Yidong <cyd <at> stupidchicken.com>
To: Kevin Ryde <user42 <at> zip.com.au>
Cc: 2631-done <at> debbugs.gnu.org, 3911-done <at> debbugs.gnu.org
Subject: Re: get-free-disk-space when default-directory doesn't exist
Date: Sat, 15 Aug 2009 20:34:52 -0400

> What is it that's not good about "/"?  It doesn't have to be readable
> or anything I don't think, just somewhere capable of a chdir()...  If
> both default-directory and home directory both don't exist
> get-free-disk-space still gets an error

You're right; it's probably better to fall back on / instead of ~.  I've
just checked in your suggested change.

> (let ((default-directory "/no/such/dir"))
>   (get-free-disk-space "."))
> => 3705637

I checked in your suggestion to do expand-file-name before changing the
default-directory, as well.  Thanks.

[Message part 3 (message/rfc822, inline)]

From: Kevin Ryde <user42 <at> zip.com.au>
To: emacs-pretest-bug <at> gnu.org
Subject: 23.1.50; get-free-disk-space relative to non-existent default-directory
Date: Fri, 24 Jul 2009 08:19:54 +1000

[Message part 4 (text/plain, inline)]

On a non-existent directory get-free-disk-space returns nil, eg.

    (get-free-disk-space "/no/such/dir")
    => nil

But if it's done by a relative path from a default-directory which
doesn't exist, then the answer is the space in your home directory

    (let ((default-directory "/no/such/dir"))
      (get-free-disk-space "."))
    => 3705637

I hoped the two answers would be the same.

This is with the "df"-running code in get-free-disk-space, ie. no
`file-system-info' function.

Perhaps absolutize per below with an inserted setq, the diff being just
re-indent.

(I still think the use of the home dir there is either complicated and
unnecessary, or complicated and necessary everywhere.  Or maybe better
call-process could not attempt a chdir at all if a caller doesn't care
about the current directory.  But leaving that unchanged as yet.)

2009-07-24  Kevin Ryde  <user42 <at> zip.com.au>

	* files.el (get-free-disk-space): Absolutize the dir before
	changing default-directory, so as not to answer about a different
	directory.

[files.el.disk-space-absolutize.diff (text/x-diff, inline)]

*** files.el	24 Jul 2009 07:35:37 +1000	1.1063
--- files.el	24 Jul 2009 08:07:01 +1000	
***************
*** 5394,5410 ****
        (save-match-data
  	(with-temp-buffer
  	  (when (and directory-free-space-program
! 		     (let ((default-directory
! 			     (if (and (not (file-remote-p default-directory))
! 				      (file-directory-p default-directory)
! 				      (file-readable-p default-directory))
! 				 default-directory
! 			       (expand-file-name "~/"))))
! 		       (eq (call-process directory-free-space-program
! 					 nil t nil
! 					 directory-free-space-args
! 					 dir)
! 			   0)))
  	    ;; Usual format is a header line followed by a line of
  	    ;; numbers.
  	    (goto-char (point-min))
--- 5394,5413 ----
        (save-match-data
  	(with-temp-buffer
  	  (when (and directory-free-space-program
!                      (progn
!                        ;; absolutize before changing default-directory
!                        (setq dir (expand-file-name dir))
!                        (let ((default-directory
!                                (if (and (not (file-remote-p default-directory))
!                                         (file-directory-p default-directory)
!                                         (file-readable-p default-directory))
!                                    default-directory
!                                  (expand-file-name "~/"))))
!                          (eq (call-process directory-free-space-program
!                                            nil t nil
!                                            directory-free-space-args
!                                            dir)
!                              0))))
  	    ;; Usual format is a header line followed by a line of
  	    ;; numbers.
  	    (goto-char (point-min))

[Message part 6 (text/plain, inline)]

In GNU Emacs 23.1.50.4 (i586-pc-linux-gnu, GTK+ Version 2.16.4)
 of 2009-07-24 on blah.blah
configured using `configure  'CFLAGS=-O -g' '--prefix=/down/emacs/b/inst' '--with-x-toolkit=gtk''

Important settings:
  value of $LC_ALL: nil
  value of $LC_COLLATE: nil
  value of $LC_CTYPE: nil
  value of $LC_MESSAGES: nil
  value of $LC_MONETARY: nil
  value of $LC_NUMERIC: nil
  value of $LC_TIME: nil
  value of $LANG: en_AU
  value of $XMODIFIERS: nil
  locale-coding-system: iso-latin-1-unix
  default-enable-multibyte-characters: t

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