Check that linux/mount.h is present before using features that rely on
it.
It is necessary to check for the presence of linux/mount.h explicitly.
Simply relying on the presence of several syscalls (e.g. SYS_move_mount,
SYS_open_tree) does not work reliably, at least not in a cross-compiling
environment.
The syscall definitions are provided by the C library. Meanwhile,
linux/mount.h is provided by the kernel. This opens the possibility for
discrepancies.
A problem arises if the C library (e.g. musl-1.2.3) defines all "mount
fd API" syscalls (and HAVE_MOUNTFD_API becomes true), but the kernel
headers are old enough to not provide linux/mount.h. The resulting error
looks as follows. This example is using an LLVM-13 cross-compiler from
x86_64 to aarch64 with musl-1.2.3 as the C library.
CC libmount/src/la-hooks.lo
In file included from libmount/src/hooks.c:30:
./include/mount-api-utils.h:11:10: fatal error: 'linux/mount.h' file not found
^~~~~~~~~~~~~~~
1 error generated.
make[4]: *** [Makefile:11185: libmount/src/la-hooks.lo] Error 1
To prevent this condition, we add a check to configure that will test
for the presence of linux/mount.h in addition to testing for the mount
fd API. Only if both conditions are met can we actually use the mount
fd API.
Signed-off-by: Markus Mayer <mmayer@xxxxxxxxxxxx>
---
configure.ac | 8 ++++++++
include/mount-api-utils.h | 4 ++--
libmount/src/hook_idmap.c | 4 ++--
libmount/src/hooks.c | 2 +-
libmount/src/version.c | 2 +-
5 files changed, 14 insertions(+), 6 deletions(-)
diff --git a/configure.ac b/configure.ac
index 11b2e155dd2d..dd582f2a4bd1 100644
--- a/configure.ac
+++ b/configure.ac
@@ -389,6 +389,12 @@ AC_CHECK_HEADERS([linux/fs.h ], [], [],
#endif
])
+AC_CHECK_HEADERS([linux/mount.h ], [], [],
+ [#ifdef HAVE_LINUX_MOUNT_H
+ # include <linux/mount.h>
+ #endif
+])
+
AC_CHECK_HEADERS([linux/gsmmux.h ], [], [],
[#ifdef LINUX_GSMMUX_H
# include <linux/gsmmux.h>
@@ -479,6 +485,7 @@ have_linux_blkzoned_h=$ac_cv_header_linux_blkzoned_h
have_linux_btrfs_h=$ac_cv_header_linux_btrfs_h
have_linux_capability_h=$ac_cv_header_linux_capability_h
have_linux_kcmp_h=$ac_cv_header_linux_kcmp_h
+have_linux_mount_h=$ac_cv_header_linux_mount_h
have_linux_pr_h=$ac_cv_header_linux_pr_h
have_linux_raw_h=$ac_cv_header_linux_raw_h
have_linux_securebits_h=$ac_cv_header_linux_securebits_h
@@ -1247,6 +1254,7 @@ UL_BUILD_INIT([libmount_mountfd_support])
UL_REQUIRES_BUILD([libmount_mountfd_support], [libmount])
UL_REQUIRES_LINUX([libmount_mountfd_support])
UL_REQUIRES_HAVE([libmount_mountfd_support], [mountfd_api], [mount FDs based API])
+UL_REQUIRES_HAVE([libmount_mountfd_support], [linux_mount_h], [linux/mount.h])
AS_IF([test "x$build_libmount_mountfd_support" = xyes ], [
AC_DEFINE([USE_LIBMOUNT_MOUNTFD_SUPPORT], [1], [Enable support for new mount FD based kernel API])
])
diff --git a/include/mount-api-utils.h b/include/mount-api-utils.h
index 9044e1cd9d61..8ae546b7ed9f 100644
--- a/include/mount-api-utils.h
+++ b/include/mount-api-utils.h
@@ -5,7 +5,7 @@
#ifndef UTIL_LINUX_MOUNT_API_UTILS
#define UTIL_LINUX_MOUNT_API_UTILS
-#ifdef HAVE_MOUNTFD_API
+#if defined(HAVE_MOUNTFD_API) && defined(HAVE_LINUX_MOUNT_H)
#include <sys/syscall.h>
#include <linux/mount.h>
@@ -203,6 +203,6 @@ static inline int fspick(int dfd, const char *pathname, unsigned int flags)
}
#endif
-#endif /* HAVE_MOUNTFD_API */
+#endif /* HAVE_MOUNTFD_API && HAVE_LINUX_MOUNT_H */
#endif /* UTIL_LINUX_MOUNT_API_UTILS */
diff --git a/libmount/src/hook_idmap.c b/libmount/src/hook_idmap.c
index b3e1d82d4b97..9b2425a77def 100644
--- a/libmount/src/hook_idmap.c
+++ b/libmount/src/hook_idmap.c
@@ -33,7 +33,7 @@
# include <linux/nsfs.h>
#endif
-#ifdef HAVE_MOUNTFD_API
+#if defined(HAVE_MOUNTFD_API) && defined(HAVE_LINUX_MOUNT_H)
typedef enum idmap_type_t {
ID_TYPE_UID, /* uidmap entry */
@@ -518,4 +518,4 @@ const struct libmnt_hookset hookset_idmap =
.deinit = hookset_deinit
};
-#endif /* HAVE_MOUNTFD_API */
+#endif /* HAVE_MOUNTFD_API && HAVE_LINUX_MOUNT_H */
diff --git a/libmount/src/hooks.c b/libmount/src/hooks.c
index 88cf68d61110..affa162d3445 100644
--- a/libmount/src/hooks.c
+++ b/libmount/src/hooks.c
@@ -46,7 +46,7 @@ static const struct libmnt_hookset *hooksets[] =
&hookset_mount,
#endif
&hookset_mount_legacy,
-#ifdef HAVE_MOUNTFD_API
+#if defined(HAVE_MOUNTFD_API) && defined(HAVE_LINUX_MOUNT_H)
&hookset_idmap,
#endif
&hookset_owner
diff --git a/libmount/src/version.c b/libmount/src/version.c
index 948b1a01de98..8e5f165f4920 100644
--- a/libmount/src/version.c
+++ b/libmount/src/version.c
@@ -38,7 +38,7 @@ static const char *lib_features[] = {
#ifdef USE_LIBMOUNT_SUPPORT_NAMESPACES
"namespaces",
#endif
-#ifdef HAVE_MOUNTFD_API
+#if defined(HAVE_MOUNTFD_API) && defined(HAVE_LINUX_MOUNT_H)
"idmapping",
#endif
#ifdef USE_LIBMOUNT_MOUNTFD_SUPPORT
--
2.40.1
