unix: split Pipe/Pipe2/Dup2, use *at replacement calls

This brings over three CLs from the main syscall package:
http://golang.org/cl/5833
http://golang.org/cl/5835
http://golang.org/cl/5837

Pipe, Pipe2, and Dup2 are moved from syscall_linux.go to the GOARCH
specific variants.  On 386 and amd64, Linux kernel version 2.6.23 (the
documented minimum Linux kernel version the Go distribution supports)
does not support the pipe2 system call, so Pipe continues to call
pipe.  On ARM, Pipe now calls pipe2.

Several system calls are reimplemented in terms of the *at syscalls,
passing AT_FDCWD to indicate that pathnames are to be interpreted
relative to the current directory.  The *at syscalls were added in
Linux kernel version 2.6.16.

This is in preparation for arm64 support, as the arm64 Linux kernel
does not provide the traditional syscall variants.

Change-Id: Id6bc6097dc5f4324cd9e429c5e1f3a411a08ce42
Reviewed-on: https://go-review.googlesource.com/10032Reviewed-by: Rob Pike <r@golang.org>

unix/syscall_linux.go

@@ -20,10 +20,38 @@ import (
  * Wrapped
  */
 
-//sys	open(path string, mode int, perm uint32) (fd int, err error)
+func Access(path string, mode uint32) (err error) {
+	return Faccessat(AT_FDCWD, path, mode, 0)
+}
+
+func Chmod(path string, mode uint32) (err error) {
+	return Fchmodat(AT_FDCWD, path, mode, 0)
+}
+
+func Chown(path string, uid int, gid int) (err error) {
+	return Fchownat(AT_FDCWD, path, uid, gid, 0)
+}
+
+func Creat(path string, mode uint32) (fd int, err error) {
+	return Open(path, O_CREAT|O_WRONLY|O_TRUNC, mode)
+}
+
+//sys	linkat(olddirfd int, oldpath string, newdirfd int, newpath string, flags int) (err error)
+
+func Link(oldpath string, newpath string) (err error) {
+	return linkat(AT_FDCWD, oldpath, AT_FDCWD, newpath, 0)
+}
+
+func Mkdir(path string, mode uint32) (err error) {
+	return Mkdirat(AT_FDCWD, path, mode)
+}
+
+func Mknod(path string, mode uint32, dev int) (err error) {
+	return Mknodat(AT_FDCWD, path, mode, dev)
+}
 
 func Open(path string, mode int, perm uint32) (fd int, err error) {
-	return open(path, mode|O_LARGEFILE, perm)
+	return openat(AT_FDCWD, path, mode|O_LARGEFILE, perm)
 }
 
 //sys	openat(dirfd int, path string, flags int, mode uint32) (fd int, err error)
@@ -32,30 +60,34 @@ func Openat(dirfd int, path string, flags int, mode uint32) (fd int, err error)
 	return openat(dirfd, path, flags|O_LARGEFILE, mode)
 }
 
-//sysnb	pipe(p *[2]_C_int) (err error)
+//sys	readlinkat(dirfd int, path string, buf []byte) (n int, err error)
 
-func Pipe(p []int) (err error) {
-	if len(p) != 2 {
-		return EINVAL
-	}
-	var pp [2]_C_int
-	err = pipe(&pp)
-	p[0] = int(pp[0])
-	p[1] = int(pp[1])
-	return
+func Readlink(path string, buf []byte) (n int, err error) {
+	return readlinkat(AT_FDCWD, path, buf)
 }
 
-//sysnb pipe2(p *[2]_C_int, flags int) (err error)
+func Rename(oldpath string, newpath string) (err error) {
+	return Renameat(AT_FDCWD, oldpath, AT_FDCWD, newpath)
+}
 
-func Pipe2(p []int, flags int) (err error) {
-	if len(p) != 2 {
-		return EINVAL
-	}
-	var pp [2]_C_int
-	err = pipe2(&pp, flags)
-	p[0] = int(pp[0])
-	p[1] = int(pp[1])
-	return
+func Rmdir(path string) error {
+	return unlinkat(AT_FDCWD, path, AT_REMOVEDIR)
+}
+
+//sys	symlinkat(oldpath string, newdirfd int, newpath string) (err error)
+
+func Symlink(oldpath string, newpath string) (err error) {
+	return symlinkat(oldpath, AT_FDCWD, newpath)
+}
+
+func Unlink(path string) error {
+	return unlinkat(AT_FDCWD, path, 0)
+}
+
+//sys	unlinkat(dirfd int, path string, flags int) (err error)
+
+func Unlinkat(dirfd int, path string) error {
+	return unlinkat(dirfd, path, 0)
 }
 
 //sys	utimes(path string, times *[2]Timeval) (err error)
@@ -789,17 +821,13 @@ func Mount(source string, target string, fstype string, flags uintptr, data stri
 /*
  * Direct access
  */
-//sys	Access(path string, mode uint32) (err error)
 //sys	Acct(path string) (err error)
 //sys	Adjtimex(buf *Timex) (state int, err error)
 //sys	Chdir(path string) (err error)
-//sys	Chmod(path string, mode uint32) (err error)
 //sys	Chroot(path string) (err error)
 //sys	ClockGettime(clockid int32, time *Timespec) (err error)
 //sys	Close(fd int) (err error)
-//sys	Creat(path string, mode uint32) (fd int, err error)
 //sys	Dup(oldfd int) (fd int, err error)
-//sys	Dup2(oldfd int, newfd int) (err error)
 //sys	Dup3(oldfd int, newfd int, flags int) (err error)
 //sysnb	EpollCreate(size int) (fd int, err error)
 //sysnb	EpollCreate1(flag int) (fd int, err error)
@@ -836,22 +864,16 @@ func Getpgrp() (pid int) {
 //sysnb	InotifyRmWatch(fd int, watchdesc uint32) (success int, err error)
 //sysnb	Kill(pid int, sig syscall.Signal) (err error)
 //sys	Klogctl(typ int, buf []byte) (n int, err error) = SYS_SYSLOG
-//sys	Link(oldpath string, newpath string) (err error)
 //sys	Listxattr(path string, dest []byte) (sz int, err error)
-//sys	Mkdir(path string, mode uint32) (err error)
 //sys	Mkdirat(dirfd int, path string, mode uint32) (err error)
-//sys	Mknod(path string, mode uint32, dev int) (err error)
 //sys	Mknodat(dirfd int, path string, mode uint32, dev int) (err error)
 //sys	Nanosleep(time *Timespec, leftover *Timespec) (err error)
 //sys	Pause() (err error)
 //sys	PivotRoot(newroot string, putold string) (err error) = SYS_PIVOT_ROOT
 //sysnb prlimit(pid int, resource int, old *Rlimit, newlimit *Rlimit) (err error) = SYS_PRLIMIT64
 //sys	read(fd int, p []byte) (n int, err error)
-//sys	Readlink(path string, buf []byte) (n int, err error)
 //sys	Removexattr(path string, attr string) (err error)
-//sys	Rename(oldpath string, newpath string) (err error)
 //sys	Renameat(olddirfd int, oldpath string, newdirfd int, newpath string) (err error)
-//sys	Rmdir(path string) (err error)
 //sys	Setdomainname(p []byte) (err error)
 //sys	Sethostname(p []byte) (err error)
 //sysnb	Setpgid(pid int, pgid int) (err error)
@@ -873,7 +895,6 @@ func Setgid(uid int) (err error) {
 
 //sys	Setpriority(which int, who int, prio int) (err error)
 //sys	Setxattr(path string, attr string, data []byte, flags int) (err error)
-//sys	Symlink(oldpath string, newpath string) (err error)
 //sys	Sync()
 //sysnb	Sysinfo(info *Sysinfo_t) (err error)
 //sys	Tee(rfd int, wfd int, len int, flags int) (n int64, err error)
@@ -881,8 +902,6 @@ func Setgid(uid int) (err error) {
 //sysnb	Times(tms *Tms) (ticks uintptr, err error)
 //sysnb	Umask(mask int) (oldmask int)
 //sysnb	Uname(buf *Utsname) (err error)
-//sys	Unlink(path string) (err error)
-//sys	Unlinkat(dirfd int, path string, flags int) (err error)
 //sys	Unmount(target string, flags int) (err error) = SYS_UMOUNT2
 //sys	Unshare(flags int) (err error)
 //sys	Ustat(dev int, ubuf *Ustat_t) (err error)

unix/syscall_linux_386.go

@@ -31,9 +31,35 @@ func NsecToTimeval(nsec int64) (tv Timeval) {
 	return
 }
 
+//sysnb	pipe(p *[2]_C_int) (err error)
+
+func Pipe(p []int) (err error) {
+	if len(p) != 2 {
+		return EINVAL
+	}
+	var pp [2]_C_int
+	err = pipe(&pp)
+	p[0] = int(pp[0])
+	p[1] = int(pp[1])
+	return
+}
+
+//sysnb pipe2(p *[2]_C_int, flags int) (err error)
+
+func Pipe2(p []int, flags int) (err error) {
+	if len(p) != 2 {
+		return EINVAL
+	}
+	var pp [2]_C_int
+	err = pipe2(&pp, flags)
+	p[0] = int(pp[0])
+	p[1] = int(pp[1])
+	return
+}
+
 // 64-bit file system and 32-bit uid calls
 // (386 default is 32-bit file system and 16-bit uid).
-//sys	Chown(path string, uid int, gid int) (err error) = SYS_CHOWN32
+//sys	Dup2(oldfd int, newfd int) (err error)
 //sys	Fadvise(fd int, offset int64, length int64, advice int) (err error) = SYS_FADVISE64_64
 //sys	Fchown(fd int, uid int, gid int) (err error) = SYS_FCHOWN32
 //sys	Fstat(fd int, stat *Stat_t) (err error) = SYS_FSTAT64

unix/syscall_linux_amd64.go

@@ -6,7 +6,7 @@ package unix
 
 import "syscall"
 
-//sys	Chown(path string, uid int, gid int) (err error)
+//sys	Dup2(oldfd int, newfd int) (err error)
 //sys	Fadvise(fd int, offset int64, length int64, advice int) (err error) = SYS_FADVISE64
 //sys	Fchown(fd int, uid int, gid int) (err error)
 //sys	Fstat(fd int, stat *Stat_t) (err error)
@@ -100,6 +100,32 @@ func NsecToTimeval(nsec int64) (tv Timeval) {
 	return
 }
 
+//sysnb	pipe(p *[2]_C_int) (err error)
+
+func Pipe(p []int) (err error) {
+	if len(p) != 2 {
+		return EINVAL
+	}
+	var pp [2]_C_int
+	err = pipe(&pp)
+	p[0] = int(pp[0])
+	p[1] = int(pp[1])
+	return
+}
+
+//sysnb pipe2(p *[2]_C_int, flags int) (err error)
+
+func Pipe2(p []int, flags int) (err error) {
+	if len(p) != 2 {
+		return EINVAL
+	}
+	var pp [2]_C_int
+	err = pipe2(&pp, flags)
+	p[0] = int(pp[0])
+	p[1] = int(pp[1])
+	return
+}
+
 func (r *PtraceRegs) PC() uint64 { return r.Rip }
 
 func (r *PtraceRegs) SetPC(pc uint64) { r.Rip = pc }

unix/syscall_linux_arm.go

@@ -26,6 +26,30 @@ func NsecToTimeval(nsec int64) (tv Timeval) {
 	return
 }
 
+func Pipe(p []int) (err error) {
+	if len(p) != 2 {
+		return EINVAL
+	}
+	var pp [2]_C_int
+	err = pipe2(&pp, 0)
+	p[0] = int(pp[0])
+	p[1] = int(pp[1])
+	return
+}
+
+//sysnb pipe2(p *[2]_C_int, flags int) (err error)
+
+func Pipe2(p []int, flags int) (err error) {
+	if len(p) != 2 {
+		return EINVAL
+	}
+	var pp [2]_C_int
+	err = pipe2(&pp, flags)
+	p[0] = int(pp[0])
+	p[1] = int(pp[1])
+	return
+}
+
 // Underlying system call writes to newoffset via pointer.
 // Implemented in assembly to avoid allocation.
 func seek(fd int, offset int64, whence int) (newoffset int64, err syscall.Errno)
@@ -57,7 +81,7 @@ func Seek(fd int, offset int64, whence int) (newoffset int64, err error) {
 
 // 64-bit file system and 32-bit uid calls
 // (16-bit uid calls are not always supported in newer kernels)
-//sys	Chown(path string, uid int, gid int) (err error) = SYS_CHOWN32
+//sys	Dup2(oldfd int, newfd int) (err error)
 //sys	Fchown(fd int, uid int, gid int) (err error) = SYS_FCHOWN32
 //sys	Fstat(fd int, stat *Stat_t) (err error) = SYS_FSTAT64
 //sysnb	Getegid() (egid int) = SYS_GETEGID32