GNU bug report logs - #19509
[PATCH] diff: treat fifos as identical

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

From: Ondřej Svoboda <ondrej <at> svobodasoft.cz>
To: bug-diffutils <at> gnu.org
Subject: [PATCH] diff: treat fifos as identical
Date: Sun, 04 Jan 2015 22:05:17 +0100

(Continuation of the previous patch; may I ask the good people of the 
list to review both?)

This avoids unwanted "differences" like

  File dev1/fifo1 is a fifo while file dev2/fifo1 is a fifo
---
 src/diff.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/src/diff.c b/src/diff.c
index a3e1b6f..cf2c62a 100644
--- a/src/diff.c
+++ b/src/diff.c
@@ -1299,6 +1299,11 @@ compare_files (struct comparison const *parent,
 	      status = EXIT_FAILURE;
 	    }
 	}
+      else if (S_ISFIFO (cmp.file[0].stat.st_mode)
+               && S_ISFIFO (cmp.file[0].stat.st_mode))
+	{
+	  /* Both are fifos.  */
+	}
       else
 	{
 	  /* We have two files that are not to be compared.  */
-- 
2.2.1

Message #8 received at 19509 <at> debbugs.gnu.org (full text, mbox):

From: Ondřej Svoboda <ondrej <at> svobodasoft.cz>
To: 19509 <at> debbugs.gnu.org
Cc: eggert <at> cs.ucla.edu
Subject: Re: [bug-diffutils] bug#19509: [PATCH] diff: treat fifos as identical
Date: Thu, 12 Feb 2015 00:29:03 +0100

Hello Paul,

may I ask you to review this little patch (and its successor that I will 
be also bumping shortly)?

Thank you! :-)

Regards,
Ondra Svoboda

On 4.1.2015 22:05, Ondřej Svoboda wrote:
> (Continuation of the previous patch; may I ask the good people of the 
> list to review both?)
>
> This avoids unwanted "differences" like
>
>   File dev1/fifo1 is a fifo while file dev2/fifo1 is a fifo
> ---
>  src/diff.c | 5 +++++
>  1 file changed, 5 insertions(+)
>
> diff --git a/src/diff.c b/src/diff.c
> index a3e1b6f..cf2c62a 100644
> --- a/src/diff.c
> +++ b/src/diff.c
> @@ -1299,6 +1299,11 @@ compare_files (struct comparison const *parent,
>            status = EXIT_FAILURE;
>          }
>      }
> +      else if (S_ISFIFO (cmp.file[0].stat.st_mode)
> +               && S_ISFIFO (cmp.file[0].stat.st_mode))
> +    {
> +      /* Both are fifos.  */
> +    }
>        else
>      {
>        /* We have two files that are not to be compared.  */

Message #11 received at 19509 <at> debbugs.gnu.org (full text, mbox):

From: Paul Eggert <eggert <at> cs.ucla.edu>
To: Ondřej Svoboda <ondrej <at> svobodasoft.cz>, 
 19509 <at> debbugs.gnu.org
Subject: Re: [bug-diffutils] bug#19509: [PATCH] diff: treat fifos as identical
Date: Wed, 11 Feb 2015 15:30:49 -0800

Ondřej Svoboda wrote:
>       }
> +      else if (S_ISFIFO (cmp.file[0].stat.st_mode)
> +               && S_ISFIFO (cmp.file[0].stat.st_mode))
> +    {
> +      /* Both are fifos.  */
> +    }

If they're the *same* fifo, they should compare the same (and already do, if I'm 
not mistaken).  But if they're *different* fifos?

Message #14 received at 19509 <at> debbugs.gnu.org (full text, mbox):

From: Ondřej Svoboda <ondrej <at> svobodasoft.cz>
To: Paul Eggert <eggert <at> cs.ucla.edu>, 19509 <at> debbugs.gnu.org
Subject: Re: [bug-diffutils] bug#19509: [PATCH] diff: treat fifos as identical
Date: Thu, 12 Feb 2015 00:37:22 +0100

I also posed this question to myself -- how can we tell two fifos apart? 
Do they by any chance store e.g. a file descriptor when they are being used?

I am not aware of any comparison done to fifos but I may as well be wrong.

On 12.2.2015 00:30, Paul Eggert wrote:
> Ondřej Svoboda wrote:
>>       }
>> +      else if (S_ISFIFO (cmp.file[0].stat.st_mode)
>> +               && S_ISFIFO (cmp.file[0].stat.st_mode))
>> +    {
>> +      /* Both are fifos.  */
>> +    }
>
> If they're the *same* fifo, they should compare the same (and already 
> do, if I'm not mistaken).  But if they're *different* fifos?
>

Message #17 received at 19509 <at> debbugs.gnu.org (full text, mbox):

From: Eric Blake <eblake <at> redhat.com>
To: Ondřej Svoboda <ondrej <at> svobodasoft.cz>,
 Paul Eggert <eggert <at> cs.ucla.edu>, 19509 <at> debbugs.gnu.org
Subject: Re: [bug-diffutils] bug#19509: bug#19509: [PATCH] diff: treat fifos
 as identical
Date: Wed, 11 Feb 2015 17:25:42 -0700

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

On 02/11/2015 04:37 PM, Ondřej Svoboda wrote:
> I also posed this question to myself -- how can we tell two fifos apart?
> Do they by any chance store e.g. a file descriptor when they are being
> used?
> 
> I am not aware of any comparison done to fifos but I may as well be wrong.

fstat() will tell you if two fds are the same fifo - their st_dev and
st_ino will be equal.

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

[signature.asc (application/pgp-signature, attachment)]

Message #20 received at 19509 <at> debbugs.gnu.org (full text, mbox):

From: Ondřej Svoboda <ondrej <at> svobodasoft.cz>
To: Eric Blake <eblake <at> redhat.com>, Paul Eggert <eggert <at> cs.ucla.edu>, 
 19509 <at> debbugs.gnu.org
Subject: Re: [bug-diffutils] bug#19509: bug#19509: [PATCH] diff: treat fifos
 as identical
Date: Thu, 12 Feb 2015 05:22:11 +0100

Thank you, Eric!

I will try it out.

On 12.2.2015 01:25, Eric Blake wrote:
> On 02/11/2015 04:37 PM, Ondřej Svoboda wrote:
>> I also posed this question to myself -- how can we tell two fifos apart?
>> Do they by any chance store e.g. a file descriptor when they are being
>> used?
>>
>> I am not aware of any comparison done to fifos but I may as well be wrong.
> fstat() will tell you if two fds are the same fifo - their st_dev and
> st_ino will be equal.
>

Message #23 received at 19509 <at> debbugs.gnu.org (full text, mbox):

From: Jim Meyering <jim <at> meyering.net>
To: Ondřej Svoboda <ondrej <at> svobodasoft.cz>
Cc: Paul Eggert <eggert <at> cs.ucla.edu>, Eric Blake <eblake <at> redhat.com>,
 19509 <at> debbugs.gnu.org
Subject: Re: [bug-diffutils] bug#19509: bug#19509: bug#19509: [PATCH] diff:
 treat fifos as identical
Date: Fri, 5 May 2017 09:40:12 -0700

close 19509
tags 19509 notabug
thanks

On Wed, Feb 11, 2015 at 8:22 PM, Ondřej Svoboda <ondrej <at> svobodasoft.cz> wrote:
> Thank you, Eric!
>
> I will try it out.
>
>
> On 12.2.2015 01:25, Eric Blake wrote:
>>
>> On 02/11/2015 04:37 PM, Ondřej Svoboda wrote:
>>>
>>> I also posed this question to myself -- how can we tell two fifos apart?
>>> Do they by any chance store e.g. a file descriptor when they are being
>>> used?
>>>
>>> I am not aware of any comparison done to fifos but I may as well be
>>> wrong.
>>
>> fstat() will tell you if two fds are the same fifo - their st_dev and
>> st_ino will be equal.

As far as I can see, diff already does the right thing: If the two
fifos are the same dev/ino, it doesn't even read them and exits 0.
Otherwise, it reads each and compares, just as for other types of files.

I'm marking this auto-created issue as "done", and "notabug", but feel
free to comment here.

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