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doc,udp: note that suggested_size is 1 max-sized dgram

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The intention here is to make working with recvmmsg more
straight-forward, since internally libuv expects buffers that are
multiples of UV__UDP_DGRAM_MAXSIZE, but previously the availability of
that value wasn't readily apparent to the caller.

Closes: https://github.com/libuv/libuv/issues/2822
Closes: https://github.com/libuv/libuv/issues/1025
Closes: https://github.com/libuv/libuv/pull/1114
PR-URL: https://github.com/libuv/libuv/pull/2986
Reviewed-By: Jameson Nash <vtjnash@gmail.com>
This commit is contained in:
Ryan Liptak 2021-07-13 08:20:53 -07:00 committed by GitHub
parent 03f1a6979c
commit 5c85d67bc7
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4 changed files with 9 additions and 4 deletions
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5
docs/src/udp.rst
View File

@ -404,6 +404,11 @@ API
:returns: 0 on success, or an error code < 0 on failure.
.. note::
When using :man:`recvmmsg(2)`, the number of messages received at a time is limited
by the number of max size dgrams that will fit into the buffer allocated in `alloc_cb`, and
`suggested_size` in `alloc_cb` for udp_recv is always set to the size of 1 max size dgram.
.. versionchanged:: 1.35.0 added support for :man:`recvmmsg(2)` on supported platforms).
The use of this feature requires a buffer larger than
2 * 64KB to be passed to `alloc_cb`.

2
src/unix/udp.c
View File

@ -32,8 +32,6 @@
#endif
#include <sys/un.h>
#define UV__UDP_DGRAM_MAXSIZE (64 * 1024)
#if defined(IPV6_JOIN_GROUP) && !defined(IPV6_ADD_MEMBERSHIP)
# define IPV6_ADD_MEMBERSHIP IPV6_JOIN_GROUP
#endif

2
src/uv-common.h
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@ -68,6 +68,8 @@ extern int snprintf(char*, size_t, const char*, ...);
#define uv__store_relaxed(p, v) do *p = v; while (0)
#endif
#define UV__UDP_DGRAM_MAXSIZE (64 * 1024)
/* Handle flags. Some flags are specific to Windows or UNIX. */
enum {
/* Used by all handles. */

4
src/win/udp.c
View File

@ -284,7 +284,7 @@ static void uv_udp_queue_recv(uv_loop_t* loop, uv_udp_t* handle) {
handle->flags &= ~UV_HANDLE_ZERO_READ;
handle->recv_buffer = uv_buf_init(NULL, 0);
handle->alloc_cb((uv_handle_t*) handle, 65536, &handle->recv_buffer);
handle->alloc_cb((uv_handle_t*) handle, UV__UDP_DGRAM_MAXSIZE, &handle->recv_buffer);
if (handle->recv_buffer.base == NULL || handle->recv_buffer.len == 0) {
handle->recv_cb(handle, UV_ENOBUFS, &handle->recv_buffer, NULL, 0);
return;
@ -501,7 +501,7 @@ void uv_process_udp_recv_req(uv_loop_t* loop, uv_udp_t* handle,
/* Do a nonblocking receive.
* TODO: try to read multiple datagrams at once. FIONREAD maybe? */
buf = uv_buf_init(NULL, 0);
handle->alloc_cb((uv_handle_t*) handle, 65536, &buf);
handle->alloc_cb((uv_handle_t*) handle, UV__UDP_DGRAM_MAXSIZE, &buf);
if (buf.base == NULL || buf.len == 0) {
handle->recv_cb(handle, UV_ENOBUFS, &buf, NULL, 0);
goto done;