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build: auto-detect the presence of the openat2() syscall #925

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build: auto-detect the presence of the openat2() syscall #925

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c4ebb84
build: auto-detect the presence of the openat2() syscall
May 28, 2026
fcd22c4
t_chmod_secure: use HAVE_OPENAT2 to check for openat2() support
May 29, 2026
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17 changes: 13 additions & 4 deletions configure.ac
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Original file line number Diff line number Diff line change
Expand Up @@ -103,10 +103,6 @@ dnl (and coverage-counted) without needing a pre-5.6 kernel. Behaviour-neutral
dnl by default (the knob only REMOVES a tier when explicitly disabled).
AC_ARG_ENABLE(openat2,
AS_HELP_STRING([--disable-openat2],[do not use Linux openat2(RESOLVE_BENEATH); force the portable resolver (for exercising the fallback tier)]))
if test x"$enable_openat2" != x"no"; then
AC_DEFINE([HAVE_OPENAT2], 1,
[Define to use Linux openat2(RESOLVE_BENEATH) in secure_relative_open where available.])
fi

AC_MSG_CHECKING([if md2man can create manpages])
if test x"$ac_cv_path_PYTHON3" = x; then
Expand Down Expand Up @@ -357,6 +353,19 @@ AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[ ]], [[return 0;]])],
CFLAGS="$OLD_CFLAGS"
AC_SUBST(NOEXECSTACK)

AC_CACHE_CHECK([for openat2],rsync_cv_HAVE_OPENAT2,[
AC_COMPILE_IFELSE([
AC_LANG_PROGRAM([[#include <sys/syscall.h>]], [[int i = SYS_openat2]])
],
[rsync_cv_HAVE_OPENAT2=yes], [rsync_cv_HAVE_OPENAT2=no])
])
if test x"$enable_openat2" != x"no"; then
if test x"$rsync_cv_HAVE_OPENAT2" = x"yes"; then
AC_DEFINE([HAVE_OPENAT2], 1,
[Define to use Linux openat2(RESOLVE_BENEATH) in secure_relative_open where available.])
fi
fi

# arrgh. libc in some old debian version screwed up the largefile
# stuff, getting byte range locking wrong
AC_CACHE_CHECK([for broken largefile support],rsync_cv_HAVE_BROKEN_LARGEFILE,[
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4 changes: 2 additions & 2 deletions t_chmod_secure.c
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Original file line number Diff line number Diff line change
Expand Up @@ -17,7 +17,7 @@

#include <sys/stat.h>

#ifdef __linux__
#if defined(__linux__) && defined(HAVE_OPENAT2)
#include <sys/syscall.h>
#include <linux/openat2.h>
#endif
Expand Down Expand Up @@ -45,7 +45,7 @@ static int errs = 0;
static int kernel_resolve_beneath_supported(void)
{
int fd;
#ifdef __linux__
#if defined(__linux__) && defined(HAVE_OPENAT2)
{
struct open_how how;
memset(&how, 0, sizeof how);
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