Re: [Qemu-devel] [PATCH v2] qemu-io: Reinitialize optind to 1 (not 0) before parsing inner command.

[Eric Blake <eblake@redhat.com>]

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On 1/7/19 11:50 AM, Max Reitz wrote:

>>>> Note I didn't set optreset.  It's not present in glibc and the "hard
>>>> reset" is not necessary in this context.
>>>
>>> But it sure sounds like FreeBSD requires you to set it, doesn't it?

No.  Quoting https://www.freebsd.org/cgi/man.cgi?getopt(3)

     The variables opterr and optind are both initialized to 1.	 The optind
     variable may be set to another value before a set of calls	to
getopt() in
     order to skip over	more or	less argv entries.

so resetting it to 1 as a soft reset is no different to setting it to 2
to skip argv[1].  It just means that you didn't get the hard reset of
internal state (there is definitely internal state if argv[1] was merged
short options - but that state is cleared if you run getopt() until it
returns -1; there may also be internal state if you used extensions, but
when you don't use extensions, such internal state is irrelevant).

I think the BSD man page needs updating, and that will probably happen
if I file my promised POSIX defect.


>> At the end of the day, both GNU optind=0 and BSD optreset=1 are
>> sufficient to force a hard reset of all hidden state.  But if you don't
>> use POSIX extensions, and always run getopt() until a -1 return, then
>> setting optind=1 is a portable soft reset, regardless of how the hidden
>> state is implemented, and regardless of how (or even if) libc offers a
>> hard reset, even though POSIX itself is currently lacking that mention.
>> (I should probably file a POSIX defect to get that wording listed in POSIX)
> 
> Hm, OK?  Is there any guarantee for that behavior for FreeBSD, or is
> that just how it is?  Because the man page is very clear on it:
> "optreset must be set to 1".  It doesn't talk about soft or hard resets
> like the glibc man page does.
> 
> And if optreset not being available for glibc is the only issue, I'd say
> adding it as a weak global variable would work without #ifdefs.

I don't see the point - Richard has already tested that optind = 1
worked on BSD machines for our purposes, so we don't have to worry about
the hard reset aspect of optreset=1.  (But yes, it would also be nice if
BSD and glibc folks could agree on how to do hard resets, instead of
having two different incompatible ways).

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org


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