unix: add mount_setattr support for linux

This brings in mount_setattr(2) support, added to Linux 5.12 kernel and
documented at https://man7.org/linux/man-pages/man2/mount_setattr.2.html

Change-Id: I5609980c18aef80f9429a8c8cec8c1e129f74ab7
Reviewed-on: https://go-review.googlesource.com/c/sys/+/363444
Reviewed-by: Ian Lance Taylor <[email protected]>
Reviewed-by: Tobias Klauser <[email protected]>
Run-TryBot: Tobias Klauser <[email protected]>

Author: kolyshkin

unix/linux/types.go

@@ -877,6 +877,8 @@ const (
 	AT_STATX_FORCE_SYNC   = C.AT_STATX_FORCE_SYNC
 	AT_STATX_DONT_SYNC    = C.AT_STATX_DONT_SYNC
 
+	AT_RECURSIVE = C.AT_RECURSIVE
+
 	AT_SYMLINK_FOLLOW   = C.AT_SYMLINK_FOLLOW
 	AT_SYMLINK_NOFOLLOW = C.AT_SYMLINK_NOFOLLOW
 
@@ -3865,3 +3867,7 @@ const (
 	SHM_RDONLY = C.SHM_RDONLY
 	SHM_RND    = C.SHM_RND
 )
+
+// mount_setattr
+
+type MountAttr C.struct_mount_attr

unix/mkerrors.sh

@@ -239,6 +239,7 @@ struct ltchars {
 #include <linux/magic.h>
 #include <linux/memfd.h>
 #include <linux/module.h>
+#include <linux/mount.h>
 #include <linux/netfilter/nfnetlink.h>
 #include <linux/netlink.h>
 #include <linux/net_namespace.h>
@@ -520,7 +521,7 @@ ccflags="$@"
 		$2 ~ /^HW_MACHINE$/ ||
 		$2 ~ /^SYSCTL_VERS/ ||
 		$2 !~ "MNT_BITS" &&
-		$2 ~ /^(MS|MNT|UMOUNT)_/ ||
+		$2 ~ /^(MS|MNT|MOUNT|UMOUNT)_/ ||
 		$2 ~ /^NS_GET_/ ||
 		$2 ~ /^TUN(SET|GET|ATTACH|DETACH)/ ||
 		$2 ~ /^(O|F|[ES]?FD|NAME|S|PTRACE|PT|TFD)_/ ||

unix/syscall_linux.go

@@ -1775,6 +1775,16 @@ func Mount(source string, target string, fstype string, flags uintptr, data stri
 	return mount(source, target, fstype, flags, datap)
 }
 
+//sys	mountSetattr(dirfd int, pathname string, flags uint, attr *MountAttr, size uintptr) (err error) = SYS_MOUNT_SETATTR
+
+// MountSetattr is a wrapper for mount_setattr(2).
+// https://man7.org/linux/man-pages/man2/mount_setattr.2.html
+//
+// Requires kernel >= 5.12.
+func MountSetattr(dirfd int, pathname string, flags uint, attr *MountAttr) error {
+	return mountSetattr(dirfd, pathname, flags, attr, unsafe.Sizeof(*attr))
+}
+
 func Sendfile(outfd int, infd int, offset *int64, count int) (written int, err error) {
 	if raceenabled {
 		raceReleaseMerge(unsafe.Pointer(&ioSync))