[PATCH 13/13] nss_dns: Rewrite _nss_dns_gethostbyname4_r using current interfaces
Florian Weimer
fweimer@redhat.com
Wed Aug 24 12:25:17 GMT 2022
* Siddhesh Poyarekar:
> On 2022-08-10 05:31, Florian Weimer via Libc-alpha wrote:
>
> Could you please add a comment on why a barrier is needed here?
>
>> + asm ("":::"memory");
It's a leftover from debugging. I'll drop it in a repost.
>> @@ -1236,36 +1126,32 @@ gaih_getanswer (const querybuf *answer1, int anslen1, const querybuf *answer2,
>> is a recoverable error we now return TRYAGIN even if the first
>> response was SUCCESS. */
>> - if (anslen1 > 0)
>> - status = gaih_getanswer_slice(answer1, anslen1, qname,
>> - &pat, &buffer, &buflen,
>> - errnop, h_errnop, ttlp,
>> - &first);
>> -
>> - if ((status == NSS_STATUS_SUCCESS || status == NSS_STATUS_NOTFOUND
>> - || (status == NSS_STATUS_TRYAGAIN
>> - /* We want to look at the second answer in case of an
>> - NSS_STATUS_TRYAGAIN only if the error is non-recoverable, i.e.
>> - *h_errnop is NO_RECOVERY. If not, and if the failure was due to
>> - an insufficient buffer (ERANGE), then we need to drop the results
>> - and pass on the NSS_STATUS_TRYAGAIN to the caller so that it can
>> - repeat the query with a larger buffer. */
>> - && (*errnop != ERANGE || *h_errnop == NO_RECOVERY)))
>> - && answer2 != NULL && anslen2 > 0)
>> + if (packet1len > 0)
>> {
>> - enum nss_status status2 = gaih_getanswer_slice(answer2, anslen2, qname,
>> - &pat, &buffer, &buflen,
>> - errnop, h_errnop, ttlp,
>> - &first);
>> + status = gaih_getanswer_slice (packet1, packet1len,
>> + abuf, &pat, errnop, h_errnop, ttlp, true);
>> + if (alloc_buffer_has_failed (abuf))
>> + /* Do not try parsing the second packet if a larger result
>> + buffer is needed. */
>
> NSS_STATUS_TRYAGAIN? It does the right thing in the caller
> eventually, but this doesn't seem semantically correct.
I'm going to add more comments and switch this to NSS_STATUS_TRYAGAIN.
For one of the other functions, internal NSS_STATUS_SUCCESS is the only
case in which a resize is attempted. See the code around line 267.
>> + return NSS_STATUS_SUCCESS;
>> + }
>> +
>> + if ((status == NSS_STATUS_SUCCESS || status == NSS_STATUS_NOTFOUND)
>> + && packet2 != NULL && packet2len > 0)
>> + {
>> + enum nss_status status2
>> + = gaih_getanswer_slice (packet2, packet2len,
>> + abuf, &pat, errnop, h_errnop, ttlp,
>> + /* Success means that data with a
>> + canonical name has already been
>> + stored. Do not store the name again. */
>> + status != NSS_STATUS_SUCCESS);
>> + if (alloc_buffer_has_failed (abuf))
>> + /* Let the caller implement the buffer resizing protocol. */
>> + return NSS_STATUS_SUCCESS;
>
> Same, wouldn't NSS_STATUS_TRYAGAIN be more correct here?
I think we can remove this early return because the caller ignores the
status anyway for the buffer-exhausted case, so we do not need to
special-case it here.
I'll repost this with the barrier removed and more comments added.
Thanks,
Florian
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