lwres_context.3

bind 9.3结合mysql数据库

.\" Copyright (C) 2004  Internet Systems Consortium, Inc. ("ISC")
.\" Copyright (C) 2000, 2001  Internet Software Consortium.
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.\" PERFORMANCE OF THIS SOFTWARE.
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.\" $Id: lwres_context.3,v 1.13.2.2.2.2 2004/03/08 09:05:12 marka Exp $
.\"
.TH "LWRES_CONTEXT" "3" "Jun 30, 2000" "BIND9" ""
.SH NAME
lwres_context_create, lwres_context_destroy, lwres_context_nextserial, lwres_context_initserial, lwres_context_freemem, lwres_context_allocmem, lwres_context_sendrecv \- lightweight resolver context management
.SH SYNOPSIS
\fB#include <lwres/lwres.h>
.sp
.na
lwres_result_t
lwres_context_create(lwres_context_t **contextp, void *arg, lwres_malloc_t malloc_function, lwres_free_t free_function);
.ad
.sp
.na
lwres_result_t
lwres_context_destroy(lwres_context_t **contextp);
.ad
.sp
.na
void
lwres_context_initserial(lwres_context_t *ctx, lwres_uint32_t serial);
.ad
.sp
.na
lwres_uint32_t
lwres_context_nextserial(lwres_context_t *ctx);
.ad
.sp
.na
void
lwres_context_freemem(lwres_context_t *ctx, void *mem, size_t len);
.ad
.sp
.na
void
lwres_context_allocmem(lwres_context_t *ctx, size_t len);
.ad
.sp
.na
void *
lwres_context_sendrecv(lwres_context_t *ctx, void *sendbase, int sendlen, void *recvbase, int recvlen, int *recvd_len);
.ad
\fR
.SH "DESCRIPTION"
.PP
\fBlwres_context_create()\fR
creates a
\fBlwres_context_t\fR
structure for use in lightweight resolver operations.
It holds a socket and other data needed for communicating
with a resolver daemon.
The new
\fBlwres_context_t\fR
is returned through
\fIcontextp\fR,
a pointer to a
\fBlwres_context_t\fR
pointer. This 
\fBlwres_context_t\fR
pointer must initially be NULL, and is modified 
to point to the newly created
\fBlwres_context_t\fR.
.PP
When the lightweight resolver needs to perform dynamic memory
allocation, it will call
\fImalloc_function\fR
to allocate memory and
\fIfree_function\fR
to free it. If 
\fImalloc_function\fR
and
\fIfree_function\fR
are NULL, memory is allocated using
\&.Xr malloc 3
and
\fBfree\fR(3).
It is not permitted to have a NULL
\fImalloc_function\fR
and a non-NULL
\fIfree_function\fR
or vice versa.
\fIarg\fR
is passed as the first parameter to the memory
allocation functions. 
If
\fImalloc_function\fR
and
\fIfree_function\fR
are NULL,
\fIarg\fR
is unused and should be passed as NULL.
.PP
Once memory for the structure has been allocated,
it is initialized using
\fBlwres_conf_init\fR(3)
and returned via
\fI*contextp\fR.
.PP
\fBlwres_context_destroy()\fR
destroys a 
\fBlwres_context_t\fR,
closing its socket.
\fIcontextp\fR
is a pointer to a pointer to the context that is to be destroyed.
The pointer will be set to NULL when the context has been destroyed.
.PP
The context holds a serial number that is used to identify resolver
request packets and associate responses with the corresponding requests.
This serial number is controlled using
\fBlwres_context_initserial()\fR
and
\fBlwres_context_nextserial()\fR.
\fBlwres_context_initserial()\fR
sets the serial number for context
\fI*ctx\fR
to
\fIserial\fR.
\fBlwres_context_nextserial()\fR
increments the serial number and returns the previous value.
.PP
Memory for a lightweight resolver context is allocated and freed using
\fBlwres_context_allocmem()\fR
and
\fBlwres_context_freemem()\fR.
These use whatever allocations were defined when the context was
created with
\fBlwres_context_create()\fR.
\fBlwres_context_allocmem()\fR
allocates
\fIlen\fR
bytes of memory and if successful returns a pointer to the allocated
storage.
\fBlwres_context_freemem()\fR
frees
\fIlen\fR
bytes of space starting at location
\fImem\fR.
.PP
\fBlwres_context_sendrecv()\fR
performs I/O for the context
\fIctx\fR.
Data are read and written from the context's socket.
It writes data from
\fIsendbase\fR
\(em typically a lightweight resolver query packet \(em
and waits for a reply which is copied to the receive buffer at
\fIrecvbase\fR.
The number of bytes that were written to this receive buffer is
returned in
\fI*recvd_len\fR.
.SH "RETURN VALUES"
.PP
\fBlwres_context_create()\fR
returns
LWRES_R_NOMEMORY
if memory for the
\fBstruct lwres_context\fR
could not be allocated, 
LWRES_R_SUCCESS
otherwise.
.PP
Successful calls to the memory allocator
\fBlwres_context_allocmem()\fR
return a pointer to the start of the allocated space.
It returns NULL if memory could not be allocated.
.PP
LWRES_R_SUCCESS
is returned when
\fBlwres_context_sendrecv()\fR
completes successfully.
LWRES_R_IOERROR
is returned if an I/O error occurs and
LWRES_R_TIMEOUT
is returned if
\fBlwres_context_sendrecv()\fR
times out waiting for a response.
.SH "SEE ALSO"
.PP
\fBlwres_conf_init\fR(3),
\fBmalloc\fR(3),
\fBfree\fR(3).