mirror of
https://sourceware.org/git/glibc.git
synced 2024-09-19 16:10:01 +00:00
352f4ff9a2
struct resolv_context objects provide a temporary resolver context which does not change during a name lookup operation. Only when the outmost context is created, the stub resolver configuration is verified to be current (at present, only against previous res_init calls). Subsequent attempts to obtain the context will reuse the result of the initial verification operation. struct resolv_context can also be extended in the future to store data which needs to be deallocated during thread cancellation.
96 lines
3.9 KiB
C
96 lines
3.9 KiB
C
/* Temporary, thread-local resolver state.
|
|
Copyright (C) 2017 Free Software Foundation, Inc.
|
|
This file is part of the GNU C Library.
|
|
|
|
The GNU C Library is free software; you can redistribute it and/or
|
|
modify it under the terms of the GNU Lesser General Public
|
|
License as published by the Free Software Foundation; either
|
|
version 2.1 of the License, or (at your option) any later version.
|
|
|
|
The GNU C Library is distributed in the hope that it will be useful,
|
|
but WITHOUT ANY WARRANTY; without even the implied warranty of
|
|
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
|
|
Lesser General Public License for more details.
|
|
|
|
You should have received a copy of the GNU Lesser General Public
|
|
License along with the GNU C Library; if not, see
|
|
<http://www.gnu.org/licenses/>. */
|
|
|
|
/* struct resolv_context objects are allocated on the heap,
|
|
initialized by __resolv_context_get (and its variants), and
|
|
destroyed by __resolv_context_put.
|
|
|
|
A nested call to __resolv_context_get (after another call to
|
|
__resolv_context_get without a matching __resolv_context_put call,
|
|
on the same thread) returns the original pointer, instead of
|
|
allocating a new context. This prevents unexpected reloading of
|
|
the resolver configuration. Care is taken to keep the context in
|
|
sync with the thread-local _res object. (This does not happen with
|
|
__resolv_context_get_override, and __resolv_context_get_no_inet6 may
|
|
also interpose another context object if RES_USE_INET6 needs to be
|
|
disabled.)
|
|
|
|
In contrast to struct __res_state, struct resolv_context is not
|
|
affected by ABI compatibility concerns.
|
|
|
|
For the benefit of the res_n* functions, a struct __res_state
|
|
pointer is included in the context object, and a separate
|
|
initialization function is provided. */
|
|
|
|
#ifndef _RESOLV_CONTEXT_H
|
|
#define _RESOLV_CONTEXT_H
|
|
|
|
#include <stdbool.h>
|
|
#include <stddef.h>
|
|
#include <bits/types/res_state.h>
|
|
|
|
/* Temporary resolver state. */
|
|
struct resolv_context
|
|
{
|
|
struct __res_state *resp; /* Backing resolver state. */
|
|
|
|
|
|
/* The following fields are for internal use within the
|
|
resolv_context module. */
|
|
size_t __refcount; /* Count of reusages by the get functions. */
|
|
bool __from_res; /* True if created from _res. */
|
|
|
|
/* If RES_USE_INET6 was disabled at this level, this field points to
|
|
the previous context. */
|
|
struct resolv_context *__next;
|
|
};
|
|
|
|
/* Return the current temporary resolver context, or NULL if there was
|
|
an error (indicated by errno). A call to this function must be
|
|
paired with a call to __resolv_context_put. */
|
|
struct resolv_context *__resolv_context_get (void)
|
|
__attribute__ ((warn_unused_result));
|
|
libc_hidden_proto (__resolv_context_get)
|
|
|
|
/* Deallocate the temporary resolver context. Converse of
|
|
__resolv_context_get. Restore the RES_USE_INET6 flag if necessary.
|
|
Do nothing if CTX is NULL. */
|
|
void __resolv_context_put (struct resolv_context *ctx);
|
|
libc_hidden_proto (__resolv_context_put)
|
|
|
|
/* Like __resolv_context_get, but the _res structure can be partially
|
|
initialzed and those changes will not be overwritten. */
|
|
struct resolv_context *__resolv_context_get_preinit (void)
|
|
__attribute__ ((warn_unused_result));
|
|
libc_hidden_proto (__resolv_context_get_preinit)
|
|
|
|
/* Wrap a struct __res_state object in a struct resolv_context object.
|
|
A call to this function must be paired with a call to
|
|
__resolv_context_put. */
|
|
struct resolv_context *__resolv_context_get_override (struct __res_state *)
|
|
__attribute__ ((nonnull (1), warn_unused_result));
|
|
libc_hidden_proto (__resolv_context_get_override)
|
|
|
|
/* Called during thread shutdown to free the associated resolver
|
|
context (mostly in response to cancellation, otherwise the
|
|
__resolv_context_get/__resolv_context_put pairing will already have
|
|
deallocated the context object). */
|
|
void __resolv_context_freeres (void) attribute_hidden;
|
|
|
|
#endif /* _RESOLV_CONTEXT_H */
|