Re: [PATCH for-5.1 1/8] tests-qemu-opts: Cover has_help_option(), qemu_opt_has_help_opt()

[Kevin Wolf <kwolf@redhat.com>]

Am 14.04.2020 um 22:13 hat Markus Armbruster geschrieben:
> Kevin Wolf <kwolf@redhat.com> writes:
> 
> > Am 14.04.2020 um 15:36 hat Markus Armbruster geschrieben:
> >> Kevin Wolf <kwolf@redhat.com> writes:
> >> > Am 14.04.2020 um 11:10 hat Markus Armbruster geschrieben:
> >> >> Eric Blake <eblake@redhat.com> writes:
> >> >> > On 4/9/20 10:30 AM, Markus Armbruster wrote:
> >> >> >> +        { "helpme", false, false, false },
> >> >> >> +        { "a,help", true, true, true },
> >> >> >> +        { "a=0,help,b", true, true, true },
> >> >> >> +        { "help,b=1", true, true, false },
> >> >> >> +        { "a,b,,help", false /* BUG */, true, true },
> >> >> >
> >> >> > So which way are you calling the bug?  Without looking at the code but
> >> >> > going off my intuition, I parse this as option 'a' and option
> >> >> > 'b,help'. The latter is not a normal option name because it contains a
> >> >> > ',', but is a valid option value.
> >> >> >
> >> >> > I agree that we have a bug, but I'm not yet sure in which direction
> >> >> > the bug lies (should has_help_option be fixed to report true, in which
> >> >> > case the substring ",help" has precedence over ',,' escaping; or
> >> >> > should qemu_opt_has_help_opt be fixed to report false, due to treating
> >> >> > 'b,help' after ',,' escape removal as an invalid option name).  So the
> >> >> > placement of the /* BUG */ comment matters - where you placed it, I'm
> >> >> > presuming that later in the series you change has_help_option to
> >> >> > return true, even though that goes against my intuitive parse.
> >> >> 
> >> >> In addition to the canonical QemuOpts parser opts_do_parse(), we have
> >> >> several more, and of course they all differ from the canonical one for
> >> >> corner cases.
> >> >> 
> >> >> I treat the canonical one as correct, and fix the others by eliminating
> >> >> the extra parsers.
> >> >> 
> >> >> The others are:
> >> >> 
> >> >> * has_help_option()
> >> >> 
> >> >>   Fixed in PATCH 5 by reusing the guts of opts_do_parse().
> >> >> 
> >> >> * is_valid_option_list()
> >> >> 
> >> >>   Fixed in PATCH 8 by not parsing.
> >> >> 
> >> >> * "id" extraction in opts_parse()
> >> >> 
> >> >>   Lazy hack.  Fixed in PATCH 3 by reusing the guts of opts_do_parse().
> >> >> 
> >> >> Back to your question: the value of has_help_option() differs from the
> >> >> value of qemu_opt_has_help_opt().  The latter uses the canonical parser,
> >> >> the former is one of the other parsers.  I therefore judge the latter
> >> >> right and the former wrong.
> >> >
> >> > Shouldn't we also consider what users would reasonably expect?
> >> 
> >> Of course we should consider reasonable user expectations.
> >> 
> >> Grumpy aside: when I do, I commonly run into objections that users
> >> reasonably expect things not to change.
> >
> > Fair point. It's not always easy to tell whether something should be
> > considered a bug in the external interface (and consequently be fixed)
> > or just an idiosyncrasy that people may have get used to (and therefore
> > requires deprecation before improving it).
> >
> > In this specific case, I'm not aware of empty option names actually
> > doing anything useful anywhere, so I think it might be clearer in this
> > case that it's indeed a bug.
> 
> You're right in that backward compatibility is not a convincing argument
> for stuff that has no known productive uses, and is bonkers to boot.
> 
> >> > Getting it parsed as an empty option name (I assume with a default value
> >> > of "on"?) certainly looks like something that would surprise most users
> >> > and, as you can see, even some QEMU developers.
> >> 
> >> My preferred way to address QemuOpts parsing madness is replacing it
> >> wholesale by keyval.c, but that's some time off, I'm afraid.
> >> 
> >> This series merely aims for more method to the same old madness.
> >
> > I understand. Though I think replacing with keyval will be potentially
> > less problematic if QemuOpts already behaved more similar.
> >
> > If I were writing the code, I think I would use existing bugs and
> > inconsistencies as an excuse to make QemuOpts behave more like what
> > keyval can easily handle by declaring whatever is closest to keyval as
> > the correct interpretation.
> 
> Fair enough.
> 
> However,
> 
> (1) is_valid_option_list()'s and opts_do_parse()'s parse of "a,b,,help"
>     are equidistant from keyval_parse()'s:
> 
>     opts_do_parse() splits it into four parts:
> 
>         "a"     (desugared to a=on)
>         "b"     (desugared to b=on)
>         ""      (desugared to =on)
>         "help"  (desugared to help=on)
> 
>     has_help_option() splits it into two:
> 
>         "a"
>         "b,help"
> 
>     keyval_parse() fails:
> 
>         Expected '=' after parameter 'a'
> 
>     If I it implemented boolean sugar, then it would fail at the third
>     comma, just like ",help" fails now:
> 
>         Invalid parameter ''
> 
>     Fails because ",help" does not start with a valid name.
> 
>     Thus, the answer to the question which of the two functions covered
>     by the test are wrong would be "both".

opts_do_parse() can return an error. So maybe what we should do is
rejecting empty option names there?

> (2) This series tries hard not to write QemuOpts parsing code.  It
>     throws away QemuOpts parsing code.

Arguably, an additional error is writing QemuOpts parsing code, but
maybe little enough that it's tolerable?

Kevin