[PATCH 3/4] resolv: Support clearing option flags with a “-” prefix (bug 14799)

[DJ Delorie]

Florian Weimer <fweimer@redhat.com> writes:
> I think using a “-” prefix is less confusing than introducing
> double-negation construct (“no-no-tld-query”).

> +* In /etc/resolv.conf and the RES_OPTIONS, option flags can now be
> +  prefixed with “-” to clear previously set flags.  For example, if
> +  /etc/resolv.conf contains “options no-aaaa”, a process running with
> +  the RES_OPTIONS=-no-aaaa environment variable performs AAAA DNS
> +  queries when the glibc DNS stub resolver is used.

Ok.

> diff --git a/resolv/res_init.c b/resolv/res_init.c
> -            uint8_t clear;

Ok, field removed.

>  #define STRnLEN(str) str, sizeof (str) - 1
> -            { STRnLEN ("rotate"), 0, RES_ROTATE },
> -            { STRnLEN ("edns0"), 0, RES_USE_EDNS0 },
> -            { STRnLEN ("single-request-reopen"), 0, RES_SNGLKUPREOP },
> -            { STRnLEN ("single-request"), 0, RES_SNGLKUP },
> -            { STRnLEN ("no_tld_query"), 0, RES_NOTLDQUERY },
> -            { STRnLEN ("no-tld-query"), 0, RES_NOTLDQUERY },
> -            { STRnLEN ("no-reload"), 0, RES_NORELOAD },
> -            { STRnLEN ("use-vc"), 0, RES_USEVC },
> -            { STRnLEN ("trust-ad"), 0, RES_TRUSTAD },
> -            { STRnLEN ("no-aaaa"), 0, RES_NOAAAA },
> +            { STRnLEN ("rotate"), RES_ROTATE },
> +            { STRnLEN ("edns0"),  RES_USE_EDNS0 },
> +            { STRnLEN ("single-request-reopen"), RES_SNGLKUPREOP },
> +            { STRnLEN ("single-request"), RES_SNGLKUP },
> +            { STRnLEN ("no_tld_query"), RES_NOTLDQUERY },
> +            { STRnLEN ("no-tld-query"), RES_NOTLDQUERY },
> +            { STRnLEN ("no-reload"), RES_NORELOAD },
> +            { STRnLEN ("use-vc"),  RES_USEVC },
> +            { STRnLEN ("trust-ad"), RES_TRUSTAD },
> +            { STRnLEN ("no-aaaa"), RES_NOAAAA },

Ok.  No change other than to remove the unneeded 0.

>  #define noptions (sizeof (options) / sizeof (options[0]))
> +          bool negate_option = *cp == '-';
> +          if (negate_option)
> +            ++cp;

Ok.

>            for (int i = 0; i < noptions; ++i)
>              if (strncmp (cp, options[i].str, options[i].len) == 0)
>                {
> -                if (options[i].clear)
> -                  parser->template.options &= options[i].flag;
> +                if (negate_option)
> +                  parser->template.options &= ~options[i].flag;
>                  else
>                    parser->template.options |= options[i].flag;

Ok.

> diff --git a/resolv/tst-resolv-res_init-skeleton.c b/resolv/tst-resolv-res_init-skeleton.c
> index 6bef62cde2..d3a19eb305 100644
> --- a/resolv/tst-resolv-res_init-skeleton.c
> +++ b/resolv/tst-resolv-res_init-skeleton.c
> @@ -679,6 +679,16 @@ struct test_case test_cases[] =
>       "; nameserver[0]: [192.0.2.1]:53\n",
>       .res_options = "attempts:5 ndots:3 edns0 ",
>      },
> +    {.name = "RES_OPTIONS can clear flags",
> +     .conf = "options ndots:2 use-vc no-aaaa edns0\n"
> +             "nameserver 192.0.2.1\n",
> +     .expected = "options ndots:3 use-vc\n"

> +                 "search example.com\n"
> +                 "; search[0]: example.com\n"

Where does this search come from?  Unrelated to what you're testing, but...

(ok as long as the test succeeds, I suppose :)

> +                 "nameserver 192.0.2.1\n"
> +                 "; nameserver[0]: [192.0.2.1]:53\n",
> +     .res_options = "ndots:3 -edns0 -no-aaaa",
> +    },

Otherwise OK.

LGTM
Reviewed-by: DJ Delorie <dj@redhat.com>