unix: add OpenTree on linux

This syscall is not yet described in linux man pages
(https://github.com/mkerrisk/man-pages.git)
but it was attempts to do it (https://lwn.net/Articles/829496/)
This syscall appeared in linux kernel v5.2

Change-Id: If44aa74c4ddd200831011c6c4bf4bd4fee440785
Reviewed-on: https://go-review.googlesource.com/c/sys/+/397094
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

unix/linux/types.go

@@ -902,6 +902,9 @@ const (
 	AT_SYMLINK_NOFOLLOW = C.AT_SYMLINK_NOFOLLOW
 
 	AT_EACCESS = C.AT_EACCESS
+
+	OPEN_TREE_CLONE   = C.OPEN_TREE_CLONE
+	OPEN_TREE_CLOEXEC = C.OPEN_TREE_CLOEXEC
 )
 
 type OpenHow C.struct_open_how

unix/syscall_linux.go

@@ -1860,6 +1860,7 @@ func Getpgrp() (pid int) {
 //sys	Mkdirat(dirfd int, path string, mode uint32) (err error)
 //sys	Mknodat(dirfd int, path string, mode uint32, dev int) (err error)
 //sys	Nanosleep(time *Timespec, leftover *Timespec) (err error)
+//sys	OpenTree(dfd int, fileName string, flags uint) (r int, err error)
 //sys	PerfEventOpen(attr *PerfEventAttr, pid int, cpu int, groupFd int, flags int) (fd int, err error)
 //sys	PivotRoot(newroot string, putold string) (err error) = SYS_PIVOT_ROOT
 //sysnb	Prlimit(pid int, resource int, newlimit *Rlimit, old *Rlimit) (err error) = SYS_PRLIMIT64

unix/zsyscall_linux.go

@@ -1215,6 +1215,22 @@ func Nanosleep(time *Timespec, leftover *Timespec) (err error) {
 
 // THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
 
+func OpenTree(dfd int, fileName string, flags uint) (r int, err error) {
+	var _p0 *byte
+	_p0, err = BytePtrFromString(fileName)
+	if err != nil {
+		return
+	}
+	r0, _, e1 := Syscall(SYS_OPEN_TREE, uintptr(dfd), uintptr(unsafe.Pointer(_p0)), uintptr(flags))
+	r = int(r0)
+	if e1 != 0 {
+		err = errnoErr(e1)
+	}
+	return
+}
+
+// THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
+
 func PerfEventOpen(attr *PerfEventAttr, pid int, cpu int, groupFd int, flags int) (fd int, err error) {
 	r0, _, e1 := Syscall6(SYS_PERF_EVENT_OPEN, uintptr(unsafe.Pointer(attr)), uintptr(pid), uintptr(cpu), uintptr(groupFd), uintptr(flags), 0)
 	fd = int(r0)

unix/ztypes_linux.go

@@ -750,6 +750,9 @@ const (
 
 	AT_RECURSIVE = 0x8000
 
+	OPEN_TREE_CLONE   = 0x1
+	OPEN_TREE_CLOEXEC = 0x80000
+
 	AT_SYMLINK_FOLLOW   = 0x400
 	AT_SYMLINK_NOFOLLOW = 0x100