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resolv: Support clearing option flags with a “-” prefix (bug 14799)

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I think using a “-” prefix is less confusing than introducing
double-negation construct (“no-no-tld-query”).

Reviewed-by: DJ Delorie <dj@redhat.com>
This commit is contained in:
Florian Weimer 2024-07-24 12:06:47 +02:00
parent af625987d6
commit 95f61610f3
3 changed files with 30 additions and 14 deletions
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6
NEWS
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@ -9,7 +9,11 @@ Version 2.41
Major new features: Major new features:
[Add new features here] * 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.
Deprecated and removed features, and other changes affecting compatibility: Deprecated and removed features, and other changes affecting compatibility:

28
resolv/res_init.c
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@ -682,27 +682,29 @@ res_setoptions (struct resolv_conf_parser *parser, const char *options)
{ {
char str[22]; char str[22];
uint8_t len; uint8_t len;
uint8_t clear;
unsigned long int flag; unsigned long int flag;
} options[] = { } options[] = {
#define STRnLEN(str) str, sizeof (str) - 1 #define STRnLEN(str) str, sizeof (str) - 1
{ STRnLEN ("rotate"), 0, RES_ROTATE }, { STRnLEN ("rotate"), RES_ROTATE },
{ STRnLEN ("edns0"), 0, RES_USE_EDNS0 }, { STRnLEN ("edns0"), RES_USE_EDNS0 },
{ STRnLEN ("single-request-reopen"), 0, RES_SNGLKUPREOP }, { STRnLEN ("single-request-reopen"), RES_SNGLKUPREOP },
{ STRnLEN ("single-request"), 0, RES_SNGLKUP }, { STRnLEN ("single-request"), RES_SNGLKUP },
{ STRnLEN ("no_tld_query"), 0, RES_NOTLDQUERY }, { STRnLEN ("no_tld_query"), RES_NOTLDQUERY },
{ STRnLEN ("no-tld-query"), 0, RES_NOTLDQUERY }, { STRnLEN ("no-tld-query"), RES_NOTLDQUERY },
{ STRnLEN ("no-reload"), 0, RES_NORELOAD }, { STRnLEN ("no-reload"), RES_NORELOAD },
{ STRnLEN ("use-vc"), 0, RES_USEVC }, { STRnLEN ("use-vc"), RES_USEVC },
{ STRnLEN ("trust-ad"), 0, RES_TRUSTAD }, { STRnLEN ("trust-ad"), RES_TRUSTAD },
{ STRnLEN ("no-aaaa"), 0, RES_NOAAAA }, { STRnLEN ("no-aaaa"), RES_NOAAAA },
}; };
#define noptions (sizeof (options) / sizeof (options[0])) #define noptions (sizeof (options) / sizeof (options[0]))
bool negate_option = *cp == '-';
if (negate_option)
++cp;
for (int i = 0; i < noptions; ++i) for (int i = 0; i < noptions; ++i)
if (strncmp (cp, options[i].str, options[i].len) == 0) if (strncmp (cp, options[i].str, options[i].len) == 0)
{ {
if (options[i].clear) if (negate_option)
parser->template.options &= options[i].flag; parser->template.options &= ~options[i].flag;
else else
parser->template.options |= options[i].flag; parser->template.options |= options[i].flag;
break; break;

10
resolv/tst-resolv-res_init-skeleton.c
View File

@ -679,6 +679,16 @@ struct test_case test_cases[] =
"; nameserver[0]: [192.0.2.1]:53\n", "; nameserver[0]: [192.0.2.1]:53\n",
.res_options = "attempts:5 ndots:3 edns0 ", .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"
"nameserver 192.0.2.1\n"
"; nameserver[0]: [192.0.2.1]:53\n",
.res_options = "ndots:3 -edns0 -no-aaaa",
},
{.name = "many search list entries (bug 19569)", {.name = "many search list entries (bug 19569)",
.conf = "nameserver 192.0.2.1\n" .conf = "nameserver 192.0.2.1\n"
"search corp.example.com support.example.com" "search corp.example.com support.example.com"