build: detect where struct mount_attr is declared

Fixes: #4176
Signed-off-by: Christian Brauner (Microsoft) <christian.brauner@ubuntu.com>

meson.build

@@ -593,7 +593,6 @@ decl_headers = '''
 foreach decl: [
     '__aligned_u64',
     'struct clone_args',
-    'struct mount_attr',
     'struct open_how',
     'struct rtnl_link_stats64',
 ]
@@ -613,7 +612,6 @@ foreach tuple: [
     ['struct seccomp_notif_sizes'],
     ['struct clone_args'],
     ['__aligned_u64'],
-    ['struct mount_attr'],
     ['struct open_how'],
     ['struct rtnl_link_stats64'],
 ]
@@ -633,6 +631,34 @@ foreach tuple: [
     endif
 endforeach
 
+## Types.
+decl_headers = '''
+#include <sys/mount.h>
+'''
+
+# We get -1 if the size cannot be determined
+if cc.sizeof('struct mount_attr', prefix: decl_headers, args: '-D_GNU_SOURCE') > 0
+    srcconf.set10('HAVE_' + 'struct mount_attr'.underscorify().to_upper(), true)
+    found_types += 'struct mount_attr (sys/mount.h)'
+else
+    srcconf.set10('HAVE_' + 'struct mount_attr'.underscorify().to_upper(), false)
+    missing_types += 'struct mount_attr (sys/mount.h)'
+endif
+
+## Types.
+decl_headers = '''
+#include <linux/mount.h>
+'''
+
+# We get -1 if the size cannot be determined
+if cc.sizeof('struct mount_attr', prefix: decl_headers, args: '-D_GNU_SOURCE') > 0
+    srcconf.set10('HAVE_UAPI_' + 'struct mount_attr'.underscorify().to_upper(), true)
+    found_types += 'struct mount_attr (linux/mount.h)'
+else
+    srcconf.set10('HAVE_UAPI_' + 'struct mount_attr'.underscorify().to_upper(), false)
+    missing_types += 'struct mount_attr (linux/mount.h)'
+endif
+
 ## Headers.
 foreach ident: [
     ['bpf',               '''#include <sys/syscall.h>

src/lxc/conf.c

@@ -2885,7 +2885,7 @@ static int __lxc_idmapped_mounts_child(struct lxc_handler *handler, FILE *f)
 		struct lxc_mount_options opts = {};
 		int dfd_from;
 		const char *source_relative, *target_relative;
-		struct lxc_mount_attr attr = {};
+		struct mount_attr attr = {};
 
 		ret = parse_lxc_mount_attrs(&opts, mntent.mnt_opts);
 		if (ret < 0)
@@ -3005,7 +3005,7 @@ static int __lxc_idmapped_mounts_child(struct lxc_handler *handler, FILE *f)
 
 		/* Set propagation mount options. */
 		if (opts.attr.propagation) {
-			attr = (struct lxc_mount_attr) {
+			attr = (struct mount_attr) {
 				.propagation = opts.attr.propagation,
 			};
 
@@ -4109,7 +4109,7 @@ int lxc_idmapped_mounts_parent(struct lxc_handler *handler)
 
 	for (;;) {
 		__do_close int fd_from = -EBADF, fd_userns = -EBADF;
-		struct lxc_mount_attr attr = {};
+		struct mount_attr attr = {};
 		struct lxc_mount_options opts = {};
 		ssize_t ret;
 

src/lxc/conf.h

@@ -223,7 +223,7 @@ struct lxc_mount_options {
 	unsigned long mnt_flags;
 	unsigned long prop_flags;
 	char *data;
-	struct lxc_mount_attr attr;
+	struct mount_attr attr;
 	char *raw_options;
 };
 

src/lxc/mount_utils.c

@@ -31,7 +31,7 @@ lxc_log_define(mount_utils, lxc);
  * setting in @attr_set, but must also specify MOUNT_ATTR__ATIME in the
  * @attr_clr field.
  */
-static inline void set_atime(struct lxc_mount_attr *attr)
+static inline void set_atime(struct mount_attr *attr)
 {
 	switch (attr->attr_set & MOUNT_ATTR__ATIME) {
 	case MOUNT_ATTR_RELATIME:
@@ -272,7 +272,7 @@ int create_detached_idmapped_mount(const char *path, int userns_fd,
 {
 	__do_close int fd_tree_from = -EBADF;
 	unsigned int open_tree_flags = OPEN_TREE_CLONE | OPEN_TREE_CLOEXEC;
-	struct lxc_mount_attr attr = {
+	struct mount_attr attr = {
 		.attr_set	= MOUNT_ATTR_IDMAP | attr_set,
 		.attr_clr	= attr_clr,
 		.userns_fd	= userns_fd,
@@ -335,7 +335,7 @@ int __fd_bind_mount(int dfd_from, const char *path_from, __u64 o_flags_from,
 		    __u64 attr_clr, __u64 propagation, int userns_fd,
 		    bool recursive)
 {
-	struct lxc_mount_attr attr = {
+	struct mount_attr attr = {
 		.attr_set	= attr_set,
 		.attr_clr	= attr_clr,
 		.propagation	= propagation,

src/lxc/syscall_wrappers.h

@@ -18,6 +18,12 @@
 #include "macro.h"
 #include "syscall_numbers.h"
 
+#if HAVE_STRUCT_MOUNT_ATTR
+#include <sys/mount.h>
+#elif HAVE_UAPI_STRUCT_MOUNT_ATTR
+#include <linux/mount.h>
+#endif
+
 #ifdef HAVE_LINUX_MEMFD_H
 #include <linux/memfd.h>
 #endif
@@ -210,16 +216,18 @@ extern int fsmount(int fs_fd, unsigned int flags, unsigned int attr_flags);
 /*
  * mount_setattr()
  */
-struct lxc_mount_attr {
+#if !HAVE_STRUCT_MOUNT_ATTR && !HAVE_UAPI_STRUCT_MOUNT_ATTR
+struct mount_attr {
 	__u64 attr_set;
 	__u64 attr_clr;
 	__u64 propagation;
 	__u64 userns_fd;
 };
+#endif
 
 #if !HAVE_MOUNT_SETATTR
 static inline int mount_setattr(int dfd, const char *path, unsigned int flags,
-				struct lxc_mount_attr *attr, size_t size)
+				struct mount_attr *attr, size_t size)
 {
 	return syscall(__NR_mount_setattr, dfd, path, flags, attr, size);
 }