Re: Return type of getrandom(2)

[Florian Weimer <fw-d32yF4oPJVt0XxTmqZlbVQ@public.gmane.org>]

* Andy Lutomirski:

> On Oct 8, 2016 4:17 PM, "Theodore Ts'o" <tytso-3s7WtUTddSA@public.gmane.org> wrote:
>>
>> On Sat, Oct 08, 2016 at 02:28:27PM +0200, Florian Weimer wrote:
>> > 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 think it should be ssize_t.  Having the types mismatched across the
> syscall boundary is just confusing.
>
>> (b) the maximum number of bytes returned will *always* be well
>> under INT_MAX.
>
> I would argue that this particular ship sailed when the len parameter
> was given the type size_t.  The door is open for requests bigger than
> 2GiB.  Even if Linux will never honor those requests, I see no reason
> to make their return value have a nonsensical type.

Thanks for your input.  I'm leaning towards ssize_t now as well.
Ted's getentropy example was helpful as well.
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