mirror of
https://github.com/golang/sys.git
synced 2026-01-29 07:02:06 +03:00
go.sys/plan9: delete Exec etc.
These are being deleted from go.sys because in general they can only be implemented in close coordination with the runtime. LGTM=0intro R=golang-codereviews, 0intro CC=golang-codereviews https://golang.org/cl/132810043
This commit is contained in:
Rob Pike
@@ -87,6 +87,38 @@ func copyenv() {
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}
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}
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// readdirnames returns the names of files inside the directory represented by dirfd.
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func readdirnames(dirfd int) (names []string, err error) {
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names = make([]string, 0, 100)
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var buf [STATMAX]byte
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for {
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n, e := Read(dirfd, buf[:])
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if e != nil {
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return nil, e
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}
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if n == 0 {
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break
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}
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for i := 0; i < n; {
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m, _ := gbit16(buf[i:])
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m += 2
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if m < STATFIXLEN {
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return nil, ErrBadStat
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}
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s, _, ok := gstring(buf[i+41:])
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if !ok {
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return nil, ErrBadStat
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}
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names = append(names, s)
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i += int(m)
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}
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}
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return
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}
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func Getenv(key string) (value string, found bool) {
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if len(key) == 0 {
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return "", false
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@@ -1,633 +0,0 @@
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// Copyright 2009 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Fork, exec, wait, etc.
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package plan9
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import (
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"runtime"
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"sync"
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"unsafe"
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)
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// Lock synchronizing creation of new file descriptors with fork.
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//
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// We want the child in a fork/exec sequence to inherit only the
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// file descriptors we intend. To do that, we mark all file
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// descriptors close-on-exec and then, in the child, explicitly
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// unmark the ones we want the exec'ed program to keep.
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// Unix doesn't make this easy: there is, in general, no way to
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// allocate a new file descriptor close-on-exec. Instead you
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// have to allocate the descriptor and then mark it close-on-exec.
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// If a fork happens between those two events, the child's exec
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// will inherit an unwanted file descriptor.
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//
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// This lock solves that race: the create new fd/mark close-on-exec
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// operation is done holding ForkLock for reading, and the fork itself
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// is done holding ForkLock for writing. At least, that's the idea.
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// There are some complications.
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//
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// Some system calls that create new file descriptors can block
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// for arbitrarily long times: open on a hung NFS server or named
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// pipe, accept on a socket, and so on. We can't reasonably grab
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// the lock across those operations.
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//
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// It is worse to inherit some file descriptors than others.
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// If a non-malicious child accidentally inherits an open ordinary file,
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// that's not a big deal. On the other hand, if a long-lived child
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// accidentally inherits the write end of a pipe, then the reader
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// of that pipe will not see EOF until that child exits, potentially
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// causing the parent program to hang. This is a common problem
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// in threaded C programs that use popen.
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//
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// Luckily, the file descriptors that are most important not to
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// inherit are not the ones that can take an arbitrarily long time
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// to create: pipe returns instantly, and the net package uses
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// non-blocking I/O to accept on a listening socket.
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// The rules for which file descriptor-creating operations use the
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// ForkLock are as follows:
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//
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// 1) Pipe. Does not block. Use the ForkLock.
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// 2) Socket. Does not block. Use the ForkLock.
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// 3) Accept. If using non-blocking mode, use the ForkLock.
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// Otherwise, live with the race.
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// 4) Open. Can block. Use O_CLOEXEC if available (Linux).
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// Otherwise, live with the race.
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// 5) Dup. Does not block. Use the ForkLock.
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// On Linux, could use fcntl F_DUPFD_CLOEXEC
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// instead of the ForkLock, but only for dup(fd, -1).
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var ForkLock sync.RWMutex
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// SlicePtrFromStrings converts a slice of strings to a slice of
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// pointers to NUL-terminated byte slices. If any string contains
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// a NUL byte, it returns (nil, EINVAL).
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func SlicePtrFromStrings(ss []string) ([]*byte, error) {
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var err error
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bb := make([]*byte, len(ss)+1)
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for i := 0; i < len(ss); i++ {
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bb[i], err = BytePtrFromString(ss[i])
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if err != nil {
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return nil, err
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}
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}
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bb[len(ss)] = nil
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return bb, nil
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}
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// readdirnames returns the names of files inside the directory represented by dirfd.
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func readdirnames(dirfd int) (names []string, err error) {
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names = make([]string, 0, 100)
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var buf [STATMAX]byte
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for {
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n, e := Read(dirfd, buf[:])
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if e != nil {
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return nil, e
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}
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if n == 0 {
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break
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}
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for i := 0; i < n; {
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m, _ := gbit16(buf[i:])
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m += 2
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if m < STATFIXLEN {
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return nil, ErrBadStat
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}
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s, _, ok := gstring(buf[i+41:])
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if !ok {
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return nil, ErrBadStat
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}
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names = append(names, s)
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i += int(m)
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}
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}
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return
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}
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// readdupdevice returns a list of currently opened fds (excluding stdin, stdout, stderr) from the dup device #d.
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// ForkLock should be write locked before calling, so that no new fds would be created while the fd list is being read.
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func readdupdevice() (fds []int, err error) {
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dupdevfd, err := Open("#d", O_RDONLY)
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if err != nil {
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return
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}
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defer Close(dupdevfd)
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names, err := readdirnames(dupdevfd)
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if err != nil {
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return
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}
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fds = make([]int, 0, len(names)/2)
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for _, name := range names {
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if n := len(name); n > 3 && name[n-3:n] == "ctl" {
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continue
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}
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fd := int(atoi([]byte(name)))
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switch fd {
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case 0, 1, 2, dupdevfd:
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continue
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}
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fds = append(fds, fd)
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}
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return
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}
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var startupFds []int
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// Plan 9 does not allow clearing the OCEXEC flag
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// from the underlying channel backing an open file descriptor,
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// therefore we store a list of already opened file descriptors
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// inside startupFds and skip them when manually closing descriptors
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// not meant to be passed to a child exec.
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func init() {
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startupFds, _ = readdupdevice()
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}
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// forkAndExecInChild forks the process, calling dup onto 0..len(fd)
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// and finally invoking exec(argv0, argvv, envv) in the child.
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// If a dup or exec fails, it writes the error string to pipe.
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// (The pipe write end is close-on-exec so if exec succeeds, it will be closed.)
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//
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// In the child, this function must not acquire any locks, because
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// they might have been locked at the time of the fork. This means
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// no rescheduling, no malloc calls, and no new stack segments.
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// The calls to RawSyscall are okay because they are assembly
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// functions that do not grow the stack.
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func forkAndExecInChild(argv0 *byte, argv []*byte, envv []envItem, dir *byte, attr *ProcAttr, fdsToClose []int, pipe int, rflag int) (pid int, err error) {
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// Declare all variables at top in case any
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// declarations require heap allocation (e.g., errbuf).
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var (
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r1 uintptr
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nextfd int
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i int
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clearenv int
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envfd int
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errbuf [ERRMAX]byte
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)
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// Guard against side effects of shuffling fds below.
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// Make sure that nextfd is beyond any currently open files so
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// that we can't run the risk of overwriting any of them.
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fd := make([]int, len(attr.Files))
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nextfd = len(attr.Files)
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for i, ufd := range attr.Files {
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if nextfd < int(ufd) {
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nextfd = int(ufd)
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}
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fd[i] = int(ufd)
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}
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nextfd++
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if envv != nil {
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clearenv = RFCENVG
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}
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// About to call fork.
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// No more allocation or calls of non-assembly functions.
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r1, _, _ = RawSyscall(SYS_RFORK, uintptr(RFPROC|RFFDG|RFREND|clearenv|rflag), 0, 0)
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if r1 != 0 {
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if int32(r1) == -1 {
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return 0, NewError(errstr())
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}
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// parent; return PID
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return int(r1), nil
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}
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// Fork succeeded, now in child.
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// Close fds we don't need.
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for i = 0; i < len(fdsToClose); i++ {
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r1, _, _ = RawSyscall(SYS_CLOSE, uintptr(fdsToClose[i]), 0, 0)
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if int32(r1) == -1 {
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goto childerror
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}
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}
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if envv != nil {
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// Write new environment variables.
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for i = 0; i < len(envv); i++ {
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r1, _, _ = RawSyscall(SYS_CREATE, uintptr(unsafe.Pointer(envv[i].name)), uintptr(O_WRONLY), uintptr(0666))
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if int32(r1) == -1 {
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goto childerror
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}
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envfd = int(r1)
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r1, _, _ = RawSyscall6(SYS_PWRITE, uintptr(envfd), uintptr(unsafe.Pointer(envv[i].value)), uintptr(envv[i].nvalue),
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^uintptr(0), ^uintptr(0), 0)
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if int32(r1) == -1 || int(r1) != envv[i].nvalue {
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goto childerror
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}
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r1, _, _ = RawSyscall(SYS_CLOSE, uintptr(envfd), 0, 0)
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if int32(r1) == -1 {
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goto childerror
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}
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}
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}
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// Chdir
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if dir != nil {
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r1, _, _ = RawSyscall(SYS_CHDIR, uintptr(unsafe.Pointer(dir)), 0, 0)
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if int32(r1) == -1 {
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goto childerror
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}
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}
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// Pass 1: look for fd[i] < i and move those up above len(fd)
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// so that pass 2 won't stomp on an fd it needs later.
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if pipe < nextfd {
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r1, _, _ = RawSyscall(SYS_DUP, uintptr(pipe), uintptr(nextfd), 0)
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if int32(r1) == -1 {
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goto childerror
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}
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pipe = nextfd
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nextfd++
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}
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for i = 0; i < len(fd); i++ {
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if fd[i] >= 0 && fd[i] < int(i) {
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r1, _, _ = RawSyscall(SYS_DUP, uintptr(fd[i]), uintptr(nextfd), 0)
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if int32(r1) == -1 {
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goto childerror
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}
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fd[i] = nextfd
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nextfd++
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if nextfd == pipe { // don't stomp on pipe
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nextfd++
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}
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}
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}
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// Pass 2: dup fd[i] down onto i.
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for i = 0; i < len(fd); i++ {
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if fd[i] == -1 {
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RawSyscall(SYS_CLOSE, uintptr(i), 0, 0)
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continue
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}
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if fd[i] == int(i) {
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continue
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}
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r1, _, _ = RawSyscall(SYS_DUP, uintptr(fd[i]), uintptr(i), 0)
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if int32(r1) == -1 {
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goto childerror
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}
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}
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// Pass 3: close fd[i] if it was moved in the previous pass.
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for i = 0; i < len(fd); i++ {
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if fd[i] >= 0 && fd[i] != int(i) {
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RawSyscall(SYS_CLOSE, uintptr(fd[i]), 0, 0)
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}
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}
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// Time to exec.
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r1, _, _ = RawSyscall(SYS_EXEC,
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uintptr(unsafe.Pointer(argv0)),
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uintptr(unsafe.Pointer(&argv[0])), 0)
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childerror:
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// send error string on pipe
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RawSyscall(SYS_ERRSTR, uintptr(unsafe.Pointer(&errbuf[0])), uintptr(len(errbuf)), 0)
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errbuf[len(errbuf)-1] = 0
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i = 0
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for i < len(errbuf) && errbuf[i] != 0 {
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||||
i++
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||||
}
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|
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RawSyscall6(SYS_PWRITE, uintptr(pipe), uintptr(unsafe.Pointer(&errbuf[0])), uintptr(i),
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^uintptr(0), ^uintptr(0), 0)
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for {
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RawSyscall(SYS_EXITS, 0, 0, 0)
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}
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}
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||||
func cexecPipe(p []int) error {
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e := Pipe(p)
|
||||
if e != nil {
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||||
return e
|
||||
}
|
||||
|
||||
fd, e := Open("#d/"+itoa(p[1]), O_CLOEXEC)
|
||||
if e != nil {
|
||||
Close(p[0])
|
||||
Close(p[1])
|
||||
return e
|
||||
}
|
||||
|
||||
Close(fd)
|
||||
return nil
|
||||
}
|
||||
|
||||
type envItem struct {
|
||||
name *byte
|
||||
value *byte
|
||||
nvalue int
|
||||
}
|
||||
|
||||
type ProcAttr struct {
|
||||
Dir string // Current working directory.
|
||||
Env []string // Environment.
|
||||
Files []uintptr // File descriptors.
|
||||
Sys *SysProcAttr
|
||||
}
|
||||
|
||||
type SysProcAttr struct {
|
||||
Rfork int // additional flags to pass to rfork
|
||||
}
|
||||
|
||||
var zeroProcAttr ProcAttr
|
||||
var zeroSysProcAttr SysProcAttr
|
||||
|
||||
func forkExec(argv0 string, argv []string, attr *ProcAttr) (pid int, err error) {
|
||||
var (
|
||||
p [2]int
|
||||
n int
|
||||
errbuf [ERRMAX]byte
|
||||
wmsg Waitmsg
|
||||
)
|
||||
|
||||
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, err := BytePtrFromString(argv0)
|
||||
if err != nil {
|
||||
return 0, err
|
||||
}
|
||||
argvp, err := SlicePtrFromStrings(argv)
|
||||
if err != nil {
|
||||
return 0, err
|
||||
}
|
||||
|
||||
var dir *byte
|
||||
if attr.Dir != "" {
|
||||
dir, err = BytePtrFromString(attr.Dir)
|
||||
if err != nil {
|
||||
return 0, err
|
||||
}
|
||||
}
|
||||
var envvParsed []envItem
|
||||
if attr.Env != nil {
|
||||
envvParsed = make([]envItem, 0, len(attr.Env))
|
||||
for _, v := range attr.Env {
|
||||
i := 0
|
||||
for i < len(v) && v[i] != '=' {
|
||||
i++
|
||||
}
|
||||
|
||||
envname, err := BytePtrFromString("/env/" + v[:i])
|
||||
if err != nil {
|
||||
return 0, err
|
||||
}
|
||||
envvalue := make([]byte, len(v)-i)
|
||||
copy(envvalue, v[i+1:])
|
||||
envvParsed = append(envvParsed, envItem{envname, &envvalue[0], len(v) - i})
|
||||
}
|
||||
}
|
||||
|
||||
// Acquire the fork lock to prevent other threads from creating new fds before we fork.
|
||||
ForkLock.Lock()
|
||||
|
||||
// get a list of open fds, excluding stdin,stdout and stderr that need to be closed in the child.
|
||||
// no new fds can be created while we hold the ForkLock for writing.
|
||||
openFds, e := readdupdevice()
|
||||
if e != nil {
|
||||
ForkLock.Unlock()
|
||||
return 0, e
|
||||
}
|
||||
|
||||
fdsToClose := make([]int, 0, len(openFds))
|
||||
for _, fd := range openFds {
|
||||
doClose := true
|
||||
|
||||
// exclude files opened at startup.
|
||||
for _, sfd := range startupFds {
|
||||
if fd == sfd {
|
||||
doClose = false
|
||||
break
|
||||
}
|
||||
}
|
||||
|
||||
// exclude files explicitly requested by the caller.
|
||||
for _, rfd := range attr.Files {
|
||||
if fd == int(rfd) {
|
||||
doClose = false
|
||||
break
|
||||
}
|
||||
}
|
||||
|
||||
if doClose {
|
||||
fdsToClose = append(fdsToClose, fd)
|
||||
}
|
||||
}
|
||||
|
||||
// Allocate child status pipe close on exec.
|
||||
e = cexecPipe(p[:])
|
||||
|
||||
if e != nil {
|
||||
return 0, e
|
||||
}
|
||||
fdsToClose = append(fdsToClose, p[0])
|
||||
|
||||
// Kick off child.
|
||||
pid, err = forkAndExecInChild(argv0p, argvp, envvParsed, dir, attr, fdsToClose, p[1], sys.Rfork)
|
||||
|
||||
if err != nil {
|
||||
if p[0] >= 0 {
|
||||
Close(p[0])
|
||||
Close(p[1])
|
||||
}
|
||||
ForkLock.Unlock()
|
||||
return 0, err
|
||||
}
|
||||
ForkLock.Unlock()
|
||||
|
||||
// Read child error status from pipe.
|
||||
Close(p[1])
|
||||
n, err = Read(p[0], errbuf[:])
|
||||
Close(p[0])
|
||||
|
||||
if err != nil || n != 0 {
|
||||
if n != 0 {
|
||||
err = NewError(string(errbuf[:n]))
|
||||
}
|
||||
|
||||
// Child failed; wait for it to exit, to make sure
|
||||
// the zombies don't accumulate.
|
||||
for wmsg.Pid != pid {
|
||||
Await(&wmsg)
|
||||
}
|
||||
return 0, err
|
||||
}
|
||||
|
||||
// Read got EOF, so pipe closed on exec, so exec succeeded.
|
||||
return pid, nil
|
||||
}
|
||||
|
||||
type waitErr struct {
|
||||
Waitmsg
|
||||
err error
|
||||
}
|
||||
|
||||
var procs struct {
|
||||
sync.Mutex
|
||||
waits map[int]chan *waitErr
|
||||
}
|
||||
|
||||
// startProcess starts a new goroutine, tied to the OS
|
||||
// thread, which runs the process and subsequently waits
|
||||
// for it to finish, communicating the process stats back
|
||||
// to any goroutines that may have been waiting on it.
|
||||
//
|
||||
// Such a dedicated goroutine is needed because on
|
||||
// Plan 9, only the parent thread can wait for a child,
|
||||
// whereas goroutines tend to jump OS threads (e.g.,
|
||||
// between starting a process and running Wait(), the
|
||||
// goroutine may have been rescheduled).
|
||||
func startProcess(argv0 string, argv []string, attr *ProcAttr) (pid int, err error) {
|
||||
type forkRet struct {
|
||||
pid int
|
||||
err error
|
||||
}
|
||||
|
||||
forkc := make(chan forkRet, 1)
|
||||
go func() {
|
||||
runtime.LockOSThread()
|
||||
var ret forkRet
|
||||
|
||||
ret.pid, ret.err = forkExec(argv0, argv, attr)
|
||||
// If fork fails there is nothing to wait for.
|
||||
if ret.err != nil || ret.pid == 0 {
|
||||
forkc <- ret
|
||||
return
|
||||
}
|
||||
|
||||
waitc := make(chan *waitErr, 1)
|
||||
|
||||
// Mark that the process is running.
|
||||
procs.Lock()
|
||||
if procs.waits == nil {
|
||||
procs.waits = make(map[int]chan *waitErr)
|
||||
}
|
||||
procs.waits[ret.pid] = waitc
|
||||
procs.Unlock()
|
||||
|
||||
forkc <- ret
|
||||
|
||||
var w waitErr
|
||||
for w.err == nil && w.Pid != ret.pid {
|
||||
w.err = Await(&w.Waitmsg)
|
||||
}
|
||||
waitc <- &w
|
||||
close(waitc)
|
||||
}()
|
||||
ret := <-forkc
|
||||
return ret.pid, ret.err
|
||||
}
|
||||
|
||||
// Combination of fork and exec, careful to be thread safe.
|
||||
func ForkExec(argv0 string, argv []string, attr *ProcAttr) (pid int, err error) {
|
||||
return startProcess(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 = startProcess(argv0, argv, attr)
|
||||
return pid, 0, err
|
||||
}
|
||||
|
||||
// Ordinary exec.
|
||||
func Exec(argv0 string, argv []string, envv []string) (err error) {
|
||||
if envv != nil {
|
||||
r1, _, _ := RawSyscall(SYS_RFORK, RFCENVG, 0, 0)
|
||||
if int32(r1) == -1 {
|
||||
return NewError(errstr())
|
||||
}
|
||||
|
||||
for _, v := range envv {
|
||||
i := 0
|
||||
for i < len(v) && v[i] != '=' {
|
||||
i++
|
||||
}
|
||||
|
||||
fd, e := Create("/env/"+v[:i], O_WRONLY, 0666)
|
||||
if e != nil {
|
||||
return e
|
||||
}
|
||||
|
||||
_, e = Write(fd, []byte(v[i+1:]))
|
||||
if e != nil {
|
||||
Close(fd)
|
||||
return e
|
||||
}
|
||||
Close(fd)
|
||||
}
|
||||
}
|
||||
|
||||
argv0p, err := BytePtrFromString(argv0)
|
||||
if err != nil {
|
||||
return err
|
||||
}
|
||||
argvp, err := SlicePtrFromStrings(argv)
|
||||
if err != nil {
|
||||
return err
|
||||
}
|
||||
_, _, e1 := Syscall(SYS_EXEC,
|
||||
uintptr(unsafe.Pointer(argv0p)),
|
||||
uintptr(unsafe.Pointer(&argvp[0])),
|
||||
0)
|
||||
|
||||
return e1
|
||||
}
|
||||
|
||||
// WaitProcess waits until the pid of a
|
||||
// running process is found in the queue of
|
||||
// wait messages. It is used in conjunction
|
||||
// with ForkExec/StartProcess to wait for a
|
||||
// running process to exit.
|
||||
func WaitProcess(pid int, w *Waitmsg) (err error) {
|
||||
procs.Lock()
|
||||
ch := procs.waits[pid]
|
||||
procs.Unlock()
|
||||
|
||||
var wmsg *waitErr
|
||||
if ch != nil {
|
||||
wmsg = <-ch
|
||||
procs.Lock()
|
||||
if procs.waits[pid] == ch {
|
||||
delete(procs.waits, pid)
|
||||
}
|
||||
procs.Unlock()
|
||||
}
|
||||
if wmsg == nil {
|
||||
// ch was missing or ch is closed
|
||||
return NewError("process not found")
|
||||
}
|
||||
if wmsg.err != nil {
|
||||
return wmsg.err
|
||||
}
|
||||
if w != nil {
|
||||
*w = wmsg.Waitmsg
|
||||
}
|
||||
return nil
|
||||
}
|
||||
Reference in New Issue
Block a user