Re: [PATCH] Avoid crippled getpass function on Solaris

From: Jeff King <peff@peff.net>
Date: Aug 6, 2012, 22:31 UTC
Message-ID: <20120806223113.GA16298@sigill.intra.peff.net>
In-Reply-To: <1344290892-sup-1108@pinkfloyd.chass.utoronto.ca>

On Mon, Aug 06, 2012 at 06:09:08PM -0400, Ben Walton wrote:

Show 6 quoted lines

> > I'm currently in pkgutil hell trying to remember how to get a working
> > gcc on Solaris. Bleh. What kind of OS doesn't ship with a compiler by
> > default? :)
> 
> One that's losing mindshare and isn't gaining traction? *g*  Feel free
> to message me offline if you need a hand with that.

Thanks, I figured it out (I installed opencsw's gcc, but I had no standard include files. Turns out that I needed the system/header package from upstream).

The stdio behavior on Solaris is weird. If I run this sample program:

  #include <stdio.h>
  int main(void)
  {
    FILE *fh = fopen("/dev/tty", "w+");
    char buf[32] = {0};
    fgets(buf, sizeof(buf), fh);
    fprintf(fh, "got %s\n", buf);
    return 0;
  }

on Linux, I get:

  $ ./a.out
  foo        <-- me typing
  got foo    <-- program output

On Solaris, I get:

  $ ./a.out
  foo        <-- me typing
  foo        <-- ???
  got foo    <-- program output

If you step it through the debugger, the mystery output comes as part of the fprintf, as if it is in the buffer waiting to be flushed. And indeed, if you dump the FILE handle via gdb, there is only a single buffer, and it contains "foo\n". Whereas with glibc, there are separate read/write buffers.

I suspect the single buffer is enough to handle normal files, but not bidirectional pipes where the input and output content are unrelated. I don't think Solaris is _buggy_ per se, as we have probably stepped outside the realm of what the standard promises, but it's certainly a quality-of-implementation issue.

So I think it could be solved by opening /dev/tty twice (or fdopen()ing the same descriptor twice). Or by just doing away with stdio entirely.

Looking over the code, I recall now why I used stdio: strbuf_getline requires it. These days we have strbuf_getwholeline_fd. It's slightly less efficient (it has to read() a character at a time), but since we are talking about a few characters of keyboard input, it should be OK.

-Peff