Re: Return type of getrandom(2)

* Theodore Ts'o:

On Sat, Oct 08, 2016 at 02:28:27PM +0200, Florian Weimer wrote:

quoted

The manual page says the return type of getrandom(2) is int, but
ssize_t would be more natural (see read(2) for comparison).  The
kernel uses ssize_t internally, which is converted to long on the
system call boundary.

The difference does not currently matter because the return value is
limited to much less than INT_MAX in the implementation.

Should we use int or ssize_t in the glibc system call wrapper?

I'd suggest keeping it as an int since (a) OpenBSD's getentropy(2)
returns an int, and part of the orignal design goal is to be able to
emulate OpenBSD's getentropy(2) system call via:

int getentropy(void *buf, size_t buflen)
{
	return getrandom(buf, buflen, 0);
}

But this implementation is quite wrong.  It has to look like something
like this:

int
getentropy (void *buf, size_t buflen)
{
  ssize_t ret = getrandom (buf, buflen, 0)
  if (ret < 0)
    return -1;
  if (ret < buflen)
    {
      errno = EIO;
      return -1;
    }
  return 0;
}

The ssize_t return would hint to the fact that such a wrapper is
required because the interfaces are somewhat different.

and (b) the maximum number of bytes returned will *always* be well
under INT_MAX.  I can't forsee at any point in any future or alternate
universe where getrandom() would need to return anywhere near
SHORT_MAX, let alone INT_MAX.

Right, that's true for the Linux implementation.  The question is
whether it applies to other implementations as well.  Solaris appears
to have an even lower limit.
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