lwres_context_create (3) - Linux Manuals

When the lightweight resolver needs to perform dynamic memory allocation, it will call malloc_function to allocate memory and free_function to free it. If malloc_function and free_function are NULL, memory is allocated using malloc(3). and free(3). It is not permitted to have a NULL malloc_function and a non-NULL free_function or vice versa. arg is passed as the first parameter to the memory allocation functions. If malloc_function and free_function are NULL, arg is unused and should be passed as NULL.

Once memory for the structure has been allocated, it is initialized using lwres_conf_init(3) and returned via *contextp.

lwres_context_destroy() destroys a lwres_context_t, closing its socket. contextp 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.

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 lwres_context_initserial() and lwres_context_nextserial(). lwres_context_initserial() sets the serial number for context *ctx to serial. lwres_context_nextserial() increments the serial number and returns the previous value.

Memory for a lightweight resolver context is allocated and freed using lwres_context_allocmem() and lwres_context_freemem(). These use whatever allocations were defined when the context was created with lwres_context_create(). lwres_context_allocmem() allocates len bytes of memory and if successful returns a pointer to the allocated storage. lwres_context_freemem() frees len bytes of space starting at location mem.

lwres_context_sendrecv() performs I/O for the context ctx. Data are read and written from the context's socket. It writes data from sendbase --- typically a lightweight resolver query packet --- and waits for a reply which is copied to the receive buffer at recvbase. The number of bytes that were written to this receive buffer is returned in *recvd_len.

RETURN VALUES

lwres_context_create() returns LWRES_R_NOMEMORY if memory for the struct lwres_context could not be allocated, LWRES_R_SUCCESS otherwise.

Successful calls to the memory allocator lwres_context_allocmem() return a pointer to the start of the allocated space. It returns NULL if memory could not be allocated.

LWRES_R_SUCCESS is returned when lwres_context_sendrecv() completes successfully. LWRES_R_IOERROR is returned if an I/O error occurs and LWRES_R_TIMEOUT is returned if lwres_context_sendrecv() times out waiting for a response.

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