On the Cygwin 3.3.6 machine at GitHub I see a test failure:
FAIL: test-supersede
====================
../../gltests/test-supersede-open.h:109: assertion 'fd >= 0' failed
Stack trace:
0x4049fd print_stack_trace
../../gllib/abort-debug.c:40
0x4049fd _gl_pre_abort
../../gllib/abort-debug.c:81
0x4024d6 test_open_supersede
../../gltests/test-supersede-open.h:109
0x41d77b main
../../gltests/test-supersede.c:53
According to the line numbers, the problem is with the /dev/null file name.
Here are some traces:
open_supersede(true,false)1: filename=/dev/null, flags=0x10402, mode=0666
open_supersede(true,false)1: fd = -1, errno = 17
canonicalize_filename_mode name=/dev/null : readlink: rname=/dev -> -1
canonicalize_filename_mode name=/dev/null : readlink: rname=/dev/null -> 12
SHOULD BE -1
canonicalize_filename_mode name=\Device\Null : readlink: rname=/Device -> -1
canonicalize_filename_mode name=\Device\Null : failing
open_supersede(true,false): canon_filename = (null)
../../gltests/test-supersede-open.h:109: assertion 'fd >= 0' failed
../../gltests/test-supersede-open.h:110: assertion 'write (fd, "Foobar\n", 7)
== 7' failed
The problem is that readlink of /dev/null returns \Device\Null, which is not
a usable file name in POSIX (Cygwin's own file system reports that '/Device'
does not exist).
So, to protect against this misbehaviour, I'm adding two unit tests, and as
expected they fail:
FAIL: test-canonicalize
=======================
../../gltests/test-canonicalize.c:430: assertion 'result2 != NULL' failed
FAIL test-canonicalize.exe (exit status: 139)
FAIL: test-readlink
===================
../../gltests/test-readlink.h:120: assertion 'result == -1 || buf[0] != '\\''
failed
FAIL test-readlink.exe (exit status: 1)
With a workaround in the 'readlink' module, these two tests now succeed.
2024-06-03 Bruno Haible <br...@clisp.org>
readlink: Work around a Cygwin 3.3.6 bug.
* m4/readlink.m4 (gl_FUNC_READLINK): Set REPLACE_READLINK to 1 on
Cygwin.
* lib/readlink.c (rpl_readlink): On Cygwin, for /dev/* files, don't
return results that start with a backslash.
* tests/test-readlink.h (test_readlink): Add a test of /dev/null.
* tests/test-canonicalize-lgpl.c (main): Likewise.
* tests/test-canonicalize.c (main): Likewise.
* doc/posix-functions/readlink.texi: Mention the Cygwin bug.
diff --git a/doc/posix-functions/readlink.texi
b/doc/posix-functions/readlink.texi
index 31769d5598..8fde7f58a7 100644
--- a/doc/posix-functions/readlink.texi
+++ b/doc/posix-functions/readlink.texi
@@ -18,6 +18,10 @@
On some platforms, this function returns @code{int} instead of
@code{ssize_t}:
glibc 2.4, FreeBSD 6.0, OpenBSD 6.7, Cygwin 1.5.x, AIX 7.1.
+@item
+For the file name @file{/dev/null}, this function returns @file{\Device\Null},
+which is unusable, on some platforms:
+Cygwin 3.3.6.
@end itemize
Portability problems mostly fixed by Gnulib:
diff --git a/lib/readlink.c b/lib/readlink.c
index a5369fa977..f4af30ebc4 100644
--- a/lib/readlink.c
+++ b/lib/readlink.c
@@ -98,6 +98,16 @@ rpl_readlink (char const *file, char *buf, size_t bufsize)
}
# endif
+# if defined __CYGWIN__
+ /* On Cygwin 3.3.6, readlink("/dev/null") returns "\\Device\\Null", which
+ is unusable. Better fail with EINVAL. */
+ if (r > 0 && strncmp (file, "/dev/", 5) == 0 && buf[0] == '\\')
+ {
+ errno = EINVAL;
+ return -1;
+ }
+# endif
+
return r;
}
diff --git a/m4/readlink.m4 b/m4/readlink.m4
index bc9a5deb06..7ebdb6ca14 100644
--- a/m4/readlink.m4
+++ b/m4/readlink.m4
@@ -1,5 +1,5 @@
# readlink.m4
-# serial 17
+# serial 18
dnl Copyright (C) 2003, 2007, 2009-2024 Free Software Foundation, Inc.
dnl This file is free software; the Free Software Foundation
dnl gives unlimited permission to copy and/or distribute it,
@@ -8,7 +8,7 @@
AC_DEFUN([gl_FUNC_READLINK],
[
AC_REQUIRE([gl_UNISTD_H_DEFAULTS])
- AC_REQUIRE([AC_CANONICAL_HOST]) dnl for cross-compiles
+ AC_REQUIRE([AC_CANONICAL_HOST])
AC_CHECK_FUNCS_ONCE([readlink])
if test $ac_cv_func_readlink = no; then
HAVE_READLINK=0
@@ -18,9 +18,13 @@ AC_DEFUN([gl_FUNC_READLINK]
[AC_COMPILE_IFELSE(
[AC_LANG_PROGRAM(
[[#include <unistd.h>
- /* Cause compilation failure if original declaration has wrong type. */
- ssize_t readlink (const char *, char *, size_t);]])],
+ /* Cause compilation failure if original declaration has
+ wrong type. */
+ ssize_t readlink (const char *, char *, size_t);
+ ]])
+ ],
[gl_cv_decl_readlink_works=yes], [gl_cv_decl_readlink_works=no])])
+
dnl Solaris 9 ignores trailing slash.
dnl FreeBSD 7.2 dereferences only one level of links with trailing slash.
AC_CACHE_CHECK([whether readlink handles trailing slash correctly],
@@ -31,8 +35,11 @@ AC_DEFUN([gl_FUNC_READLINK]
AC_RUN_IFELSE(
[AC_LANG_PROGRAM(
[[#include <unistd.h>
-]], [[char buf[20];
- return readlink ("conftest.lnk2/", buf, sizeof buf) != -1;]])],
+ ]],
+ [[char buf[20];
+ return readlink ("conftest.lnk2/", buf, sizeof buf) != -1;
+ ]])
+ ],
[gl_cv_func_readlink_trailing_slash=yes],
[gl_cv_func_readlink_trailing_slash=no],
[case "$host_os" in
@@ -71,8 +78,11 @@ AC_DEFUN([gl_FUNC_READLINK]
AC_RUN_IFELSE(
[AC_LANG_PROGRAM(
[[#include <unistd.h>
-]], [[char c;
- return readlink ("conftest.link", &c, 1) != 1;]])],
+ ]],
+ [[char c;
+ return readlink ("conftest.link", &c, 1) != 1;
+ ]])
+ ],
[gl_cv_func_readlink_truncate=yes],
[gl_cv_func_readlink_truncate=no],
[case "$host_os" in
@@ -103,6 +113,14 @@ AC_DEFUN([gl_FUNC_READLINK]
REPLACE_READLINK=1
;;
esac
+
+ dnl On Cygwin 3.3.6, readlink("/dev/null") returns "\\Device\\Null", which
+ dnl is unusable.
+ case "$host_os" in
+ cygwin*)
+ REPLACE_READLINK=1
+ ;;
+ esac
fi
])
diff --git a/tests/test-canonicalize-lgpl.c b/tests/test-canonicalize-lgpl.c
index 769f7c3968..923f0fb46c 100644
--- a/tests/test-canonicalize-lgpl.c
+++ b/tests/test-canonicalize-lgpl.c
@@ -283,6 +283,13 @@ main (void)
free (result2);
}
+#if !(defined _WIN32 && !defined __CYGWIN__)
+ /* Check a device file. */
+ {
+ char *result = canonicalize_file_name ("/dev/null");
+ ASSERT (result != NULL);
+ }
+#endif
/* Cleanup. */
ASSERT (remove (BASE "/droot") == 0);
diff --git a/tests/test-canonicalize.c b/tests/test-canonicalize.c
index 0224c2bbcf..71177681ae 100644
--- a/tests/test-canonicalize.c
+++ b/tests/test-canonicalize.c
@@ -421,6 +421,17 @@ main (void)
free (result4);
}
+#if !(defined _WIN32 && !defined __CYGWIN__)
+ /* Check a device file. */
+ {
+ char *result1 = canonicalize_file_name ("/dev/null");
+ char *result2 = canonicalize_filename_mode ("/dev/null", CAN_ALL_BUT_LAST);
+ ASSERT (result1 != NULL);
+ ASSERT (result2 != NULL);
+ ASSERT (strcmp (result1, result2) == 0);
+ }
+#endif
+
/* Cleanup. */
ASSERT (remove (BASE "/droot") == 0);
ASSERT (remove (BASE "/d/1") == 0);
diff --git a/tests/test-readlink.h b/tests/test-readlink.h
index c04ae311e2..d547bec959 100644
--- a/tests/test-readlink.h
+++ b/tests/test-readlink.h
@@ -113,6 +113,12 @@ test_readlink (ssize_t (*func) (char const *, char *,
size_t), bool print)
either left alone, or NUL-terminated. */
ASSERT (buf[len] == '\0' || buf[len] == (char) 0xff);
}
+ {
+ /* On Cygwin 3.3.6, readlink("/dev/null") returns "\\Device\\Null", which
+ is unusable. Verify that gnulib works around this nonsense. */
+ ssize_t result = func ("/dev/null", buf, sizeof buf);
+ ASSERT (result == -1 || buf[0] != '\\');
+ }
ASSERT (rmdir (BASE "dir") == 0);
ASSERT (unlink (BASE "link") == 0);
