Doesn't work with node v0.8.x

[dazoe]

Tested with version 0.8.8 kexec('top'); just causes the node process to die and doesn't start 'top'

I ran strace on it and it looks like it is loading and starting top but top is dying because it can't get stdio...

...
write(2, "\ttop: failed tty get\n", 21) = -1 EBADF (Bad file descriptor)
close(1)                                = -1 EBADF (Bad file descriptor)
close(2)                                = -1 EBADF (Bad file descriptor)
exit_group(1)                           = ?
+++ exited with 1 +++

works fine with node 0.6.x

[jprichardson]

Ya, I was aware that it didn't work with Node v0.8. But, I had no idea why. I tried asking here without much luck: https://groups.google.com/forum/?fromgroups=#!topic/nodejs-dev/FnLd3QQWs5Y

But, your report is helpful, because now I have some ideas to try to get this to work. Thanks!

[mattinsler]

I'd love for this to work. =-)

This doesn't solve the issue above, but to migrate to node-gyp, just do this...

Add binding.gyp:

{ "targets": [ { "target_name": "kexec", "sources": [ "src/node_kexec.cpp" ] } ] }

Change package.json to:

{ "name" : "kexec", "version" : "0.0.4", "description" : "Replace your Node.js process with another process. Like Ruby exec.", "homepage" : [ "https://github.com/jprichardson/node-kexec" ], "repository" : { "type" : "git", "url" : "https://github.com/jprichardson/node-kexec" }, "keywords" : ["exec","spawn","process"], "author" : "JP Richardson jprichardson@gmail.com", "licenses" : [ {"type" : "MIT" } ],
"main" : "./index", "engines" : { "node" : ">=0.4" }, "scripts": { "install": "node-gyp configure build" } }

[jprichardson]

Guys, I'm kinda at a loss on this one... I've tried a lot of things. Here's a dump of various things:

static Handle<Value> kexec(const Arguments& args) {
    puts("here.");
    //HandleScope scope;
    String::Utf8Value v8str(args[0]);
    //char* argv2[] = { const_cast<char *>("-c"), *v8str,  NULL};
    printf("Rar: %s\n", *v8str);
    puts("hi from mod");
    //char* argv2[] = {const_cast<char *>("-c"), *v8str, NULL};
    //char* argv3[] = { const_cast<char *>(""), const_cast<char *>("-c"), const_cast<char *>("top"), const_cast<char *>(">"), const_cast<char *>("/tmp/poo.txt"), NULL};
    char* argv4[] = {null};

    int err = execvp("/bin/bash", argv4);
    printf("Error: %d", err);      
    //int i = execvp("/usr/bin/top", argv3);
    //execlp("ps", "ps", NULL);
    //printf("Return code: %d", i);
    //return scope.Close(Undefined());//Undefined();
    //return scope.Close(String::New("world"));
    return Undefined();
}

I'm not sure where to go from here. Nothing really seems to work. What confuses me the most is I'm not sure how from @dazoe's report, bash can't get access to stdio.

Any ideas?

Thanks,

JP

[ehg]

After a quick dig, we found that commenting uv_disable_stdio_inheritance() out in node.cc seems to allow the child process access to stdio.

char** Init(int argc, char *argv[]) {
  // Initialize prog_start_time to get relative uptime.
  uv_uptime(&prog_start_time);

  // Make inherited handles noninheritable.
  uv_disable_stdio_inheritance();

[aidanhs]

The comment on uv_disable_stdio_inheritance is sadly quite terse. If you go back further you'll find https://github.com/joyent/node/commit/37d75ba241780c9199f601dd4c70713d190c68e6#L1R1581, which is a little more descriptive.

I guess node severs all ties child processes may have to node's stdin and stdout. Hence invalid file descriptors.

Digging a bit more, it seems that the reason this was added in the first place was to make a test pass - https://github.com/joyent/node/commit/09be360a0fee2c7619bae8c4248f9ed3d79d1b30. Reading that single line test description, it seems to be explicitly testing that it's impossible to do what kexec aims to do (I think?).

[jprichardson]

Hmm... so would it be possible to make a function uv_enable_stdio_inheritance() in kexec.cpp?

Here's the source for uv_disable_stdio_inheritance(): from: https://github.com/joyent/libuv/blob/master/src/unix/core.c

void uv_disable_stdio_inheritance(void) {
  int fd;

  /* Set the CLOEXEC flag on all open descriptors. Unconditionally try the
   * first 16 file descriptors. After that, bail out after the first error.
   */
  for (fd = 0; ; fd++)
    if (uv__cloexec(fd, 1) && fd > 15)
      break;
}

uv__cloexec():

int uv__cloexec(int fd, int set) {
  int r;

  do
    r = ioctl(fd, set ? FIOCLEX : FIONCLEX);
  while (r == -1 && errno == EINTR);

  return r;
}

[jprichardson]

Fixed it! Patch coming soon!

[jprichardson]

OK, patch pushed and published to NPM. Look it over and let me know if it works for you.

[aidanhs]

I think you need to edit https://github.com/jprichardson/node-kexec/commit/950a24fa56797e5dfe1b40caa9bd22d4c1ebe413#L3R12 as well?

[ehg]

Works for me, thanks!

[jprichardson]

@aidanhs I probably should have just deleted the wscript file since it's for node-waf and node-waf isn't in use by Node anymore. That file is only good for Node v0.4 compatibility in which case, the person should just run node install kexec0.0.3.