dd: don't mistakenly use O_EXCL on GNU/Hurd

[Collin Funk]

Bruno Haible via GNU coreutils General Discussion <coreutils@gnu.org>
writes:

> When I disable this test, "make check" completes, and there are
> 9 test failures:
>
> FAIL: tests/factor/factor-parallel.sh
> FAIL: tests/nice/nice.sh
> FAIL: tests/tail/tail-c.sh
> FAIL: tests/cp/parent-perm-race.sh
> FAIL: tests/cp/sparse-to-pipe.sh
> FAIL: tests/cp/special-f.sh
> FAIL: tests/dd/bytes.sh
> FAIL: tests/mv/backup-dir.sh
> FAIL: tests/mv/trailing-slash.sh
>
> Here is the relevant part of the log file.

Thanks. This patch fixes tests/dd/bytes.sh. The issue can be seen in
GDB. The 'opts' variable is what we pass to open ():

File creation flags on GNU/Hurd:

    (gdb) print /x opts
    $1 = 0x30
    print /x O_SEEK_BYTES 
    $2 = 0x20

On GNU/Hurd this is equivalent to (O_EXCL | O_CREAT). Where 0x20 is
O_EXCL and 0x10 is O_CREAT.

This causes the following on GNU/Hurd:

    $ dd seek=8 oflag=seek_bytes bs=5 of=out2 count=0 status=none 
    $ dd seek=8 oflag=seek_bytes bs=5 of=out2 count=0 status=none 
    dd: failed to open 'out2': File exists

However, on GNU/Linux we get the expected behavior, i.e. no error:

    $ dd seek=8 oflag=seek_bytes bs=5 of=out2 count=0 status=none 
    $ dd seek=8 oflag=seek_bytes bs=5 of=out2 count=0 status=none

I pushed this patch to fix it. I added a news entry referencing
Coreutils 8.16 since that was when count_bytes, and the bug would have
existed then. However, before that release it is possible there was a
similar bug.

Collin


>From 2662ddf335c9c5bafefa9c8c0b25c26e73d192ab Mon Sep 17 00:00:00 2001
Message-ID: <2662ddf335c9c5bafefa9c8c0b25c26e73d192ab.1758265313.git.collin.fu...@gmail.com>
From: Collin Funk <collin.fu...@gmail.com>
Date: Thu, 18 Sep 2025 23:29:02 -0700
Subject: [PATCH] dd: don't mistakenly use O_EXCL on GNU/Hurd

* src/dd.c (v): Add the O_EXCL flag to the set of bits that we do not
want to use for our definitions.
* cfg.mk (sc_dd_O_FLAGS): Adjust to pass syntax-check.
* NEWS: Mention the fix.
Reported by Bruno Haible.
---
 NEWS     | 4 ++++
 cfg.mk   | 3 ++-
 src/dd.c | 1 +
 3 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/NEWS b/NEWS
index 4c979607b..d618a0bdd 100644
--- a/NEWS
+++ b/NEWS
@@ -38,6 +38,10 @@ GNU coreutils NEWS                                    -*- outline -*-
   precedence.  Previously multiple specifications would induce an error.
   [bug introduced in coreutils-5.90]
 
+  'dd oflag=seek_bytes' no longer mistakenly reports errors when the
+  output file exists on GNU/Hurd.
+  [bug introduced in coreutils-8.16]
+
   'fold' no longer exhausts memory when processing large inputs
   with a very large --width argument.
   [This bug was present in "the beginning".]
diff --git a/cfg.mk b/cfg.mk
index 0abb5c226..8e8cae2e6 100644
--- a/cfg.mk
+++ b/cfg.mk
@@ -68,7 +68,8 @@ sc_dd_O_FLAGS:
 	@rm -f $@.1 $@.2
 	@{ echo O_FULLBLOCK; echo O_NOCACHE;				\
 	  perl -nle '/^ +\| (O_\w*)$$/ and print $$1' $(dd); } | sort > $@.1
-	@{ echo O_NOFOLLOW; perl -nle '/{"[a-z]+",\s*(O_\w+)},/ and print $$1' \
+	@{ echo O_NOFOLLOW; echo O_EXCL;				\
+	   perl -nle '/{"[a-z]+",\s*(O_\w+)},/ and print $$1'		\
 	  $(dd); } | sort > $@.2
 	@diff -u $@.1 $@.2; diff=$$?;					\
 	rm -f $@.1 $@.2;						\
diff --git a/src/dd.c b/src/dd.c
index 33959b495..98f360089 100644
--- a/src/dd.c
+++ b/src/dd.c
@@ -295,6 +295,7 @@ enum
           | O_DIRECT
           | O_DIRECTORY
           | O_DSYNC
+          | O_EXCL
           | O_NOATIME
           | O_NOCTTY
           | O_NOFOLLOW
-- 
2.51.0