Subversion Repositories openrisc

// Copyright 2009 The Go Authors. All rights reserved.

// Use of this source code is governed by a BSD-style

// license that can be found in the LICENSE file.

// +build darwin freebsd linux netbsd openbsd

// Fork, exec, wait, etc.

package syscall

import (

        "runtime"

        "sync"

        "unsafe"

)

//sysnb raw_fork() (pid Pid_t, err Errno)

//fork() Pid_t

//sysnb raw_setsid() (err Errno)

//setsid() Pid_t

//sysnb raw_setpgid(pid int, pgid int) (err Errno)

//setpgid(pid Pid_t, pgid Pid_t) int

//sysnb raw_chroot(path *byte) (err Errno)

//chroot(path *byte) int

//sysnb raw_chdir(path *byte) (err Errno)

//chdir(path *byte) int

//sysnb raw_fcntl(fd int, cmd int, arg int) (val int, err Errno)

//fcntl(fd int, cmd int, arg int) int

//sysnb raw_close(fd int) (err Errno)

//close(fd int) int

//sysnb raw_ioctl(fd int, cmd int, val int) (rval int, err Errno)

//ioctl(fd int, cmd int, val int) int

//sysnb raw_execve(argv0 *byte, argv **byte, envv **byte) (err Errno)

//execve(argv0 *byte, argv **byte, envv **byte) int

//sysnb raw_write(fd int, buf *byte, count int) (err Errno)

//write(fd int, buf *byte, count Size_t) Ssize_t

//sysnb raw_exit(status int)

//_exit(status int)

//sysnb raw_dup2(oldfd int, newfd int) (err Errno)

//dup2(oldfd int, newfd int) int

// Note: not raw, returns error rather than Errno.

//sys   read(fd int, p *byte, np int) (n int, err error)

//read(fd int, buf *byte, count Size_t) Ssize_t

// Lock synchronizing creation of new file descriptors with fork.

//

// We want the child in a fork/exec sequence to inherit only the

// file descriptors we intend.  To do that, we mark all file

// descriptors close-on-exec and then, in the child, explicitly

// unmark the ones we want the exec'ed program to keep.

// Unix doesn't make this easy: there is, in general, no way to

// allocate a new file descriptor close-on-exec.  Instead you

// have to allocate the descriptor and then mark it close-on-exec.

// If a fork happens between those two events, the child's exec

// will inherit an unwanted file descriptor.

//

// This lock solves that race: the create new fd/mark close-on-exec

// operation is done holding ForkLock for reading, and the fork itself

// is done holding ForkLock for writing.  At least, that's the idea.

// There are some complications.

//

// Some system calls that create new file descriptors can block

// for arbitrarily long times: open on a hung NFS server or named

// pipe, accept on a socket, and so on.  We can't reasonably grab

// the lock across those operations.

//

// It is worse to inherit some file descriptors than others.

// If a non-malicious child accidentally inherits an open ordinary file,

// that's not a big deal.  On the other hand, if a long-lived child

// accidentally inherits the write end of a pipe, then the reader

// of that pipe will not see EOF until that child exits, potentially

// causing the parent program to hang.  This is a common problem

// in threaded C programs that use popen.

//

// Luckily, the file descriptors that are most important not to

// inherit are not the ones that can take an arbitrarily long time

// to create: pipe returns instantly, and the net package uses

// non-blocking I/O to accept on a listening socket.

// The rules for which file descriptor-creating operations use the

// ForkLock are as follows:

//

// 1) Pipe.    Does not block.  Use the ForkLock.

// 2) Socket.  Does not block.  Use the ForkLock.

// 3) Accept.  If using non-blocking mode, use the ForkLock.

//             Otherwise, live with the race.

// 4) Open.    Can block.  Use O_CLOEXEC if available (GNU/Linux).

//             Otherwise, live with the race.

// 5) Dup.     Does not block.  Use the ForkLock.

//             On GNU/Linux, could use fcntl F_DUPFD_CLOEXEC

//             instead of the ForkLock, but only for dup(fd, -1).

var ForkLock sync.RWMutex

// Convert array of string to array

// of NUL-terminated byte pointer.

func StringSlicePtr(ss []string) []*byte {

        bb := make([]*byte, len(ss)+1)

        for i := 0; i < len(ss); i++ {

                bb[i] = StringBytePtr(ss[i])

        }

        bb[len(ss)] = nil

        return bb

}

func CloseOnExec(fd int) { fcntl(fd, F_SETFD, FD_CLOEXEC) }

func SetNonblock(fd int, nonblocking bool) (err error) {

        flag, err := fcntl(fd, F_GETFL, 0)

        if err != nil {

                return err

        }

        if nonblocking {

                flag |= O_NONBLOCK

        } else {

                flag &= ^O_NONBLOCK

        }

        _, err = fcntl(fd, F_SETFL, flag)

        return err

}

// Credential holds user and group identities to be assumed

// by a child process started by StartProcess.

type Credential struct {

        Uid    uint32   // User ID.

        Gid    uint32   // Group ID.

        Groups []uint32 // Supplementary group IDs.

}

// ProcAttr holds attributes that will be applied to a new process started

// by StartProcess.

type ProcAttr struct {

        Dir   string   // Current working directory.

        Env   []string // Environment.

        Files []int    // File descriptors.

        Sys   *SysProcAttr

}

var zeroProcAttr ProcAttr

var zeroSysProcAttr SysProcAttr

func forkExec(argv0 string, argv []string, attr *ProcAttr) (pid int, err error) {

        var p [2]int

        var n int

        var err1 Errno

        var wstatus WaitStatus

        if attr == nil {

                attr = &zeroProcAttr

        }

        sys := attr.Sys

        if sys == nil {

                sys = &zeroSysProcAttr

        }

        p[0] = -1

        p[1] = -1

        // Convert args to C form.

        argv0p := StringBytePtr(argv0)

        argvp := StringSlicePtr(argv)

        envvp := StringSlicePtr(attr.Env)

        if runtime.GOOS == "freebsd" && len(argv[0]) > len(argv0) {

                argvp[0] = argv0p

        }

        var chroot *byte

        if sys.Chroot != "" {

                chroot = StringBytePtr(sys.Chroot)

        }

        var dir *byte

        if attr.Dir != "" {

                dir = StringBytePtr(attr.Dir)

        }

        // Acquire the fork lock so that no other threads

        // create new fds that are not yet close-on-exec

        // before we fork.

        ForkLock.Lock()

        // Allocate child status pipe close on exec.

        if err = Pipe(p[0:]); err != nil {

                goto error

        }

        if _, err = fcntl(p[0], F_SETFD, FD_CLOEXEC); err != nil {

                goto error

        }

        if _, err = fcntl(p[1], F_SETFD, FD_CLOEXEC); err != nil {

                goto error

        }

        // Kick off child.

        pid, err1 = forkAndExecInChild(argv0p, argvp, envvp, chroot, dir, attr, sys, p[1])

        if err1 != 0 {

                goto error

        }

        ForkLock.Unlock()

        // Read child error status from pipe.

        Close(p[1])

        n, err = read(p[0], (*byte)(unsafe.Pointer(&err1)), int(unsafe.Sizeof(err1)))

        Close(p[0])

        if err != nil || n != 0 {

                if n == int(unsafe.Sizeof(err1)) {

                        err = Errno(err1)

                }

                if err == nil {

                        err = EPIPE

                }

                // Child failed; wait for it to exit, to make sure

                // the zombies don't accumulate.

                _, err1 := Wait4(pid, &wstatus, 0, nil)

                for err1 == EINTR {

                        _, err1 = Wait4(pid, &wstatus, 0, nil)

                }

                return 0, err

        }

        // Read got EOF, so pipe closed on exec, so exec succeeded.

        return pid, nil

error:

        if p[0] >= 0 {

                Close(p[0])

                Close(p[1])

        }

        ForkLock.Unlock()

        return 0, err

}

// Combination of fork and exec, careful to be thread safe.

func ForkExec(argv0 string, argv []string, attr *ProcAttr) (pid int, err error) {

        return forkExec(argv0, argv, attr)

}

// StartProcess wraps ForkExec for package os.

func StartProcess(argv0 string, argv []string, attr *ProcAttr) (pid int, handle uintptr, err error) {

        pid, err = forkExec(argv0, argv, attr)

        return pid, 0, err

}

// Ordinary exec.

func Exec(argv0 string, argv []string, envv []string) (err error) {

        err1 := raw_execve(StringBytePtr(argv0),

                &StringSlicePtr(argv)[0],

                &StringSlicePtr(envv)[0])

        return Errno(err1)

}