[FFmpeg-devel] [PATCH] WIP: udp.c: take into account doubling of SO_RCVBUF size (PR #21235)

[igutidze via ffmpeg-devel <ffmpeg-devel@ffmpeg.org>]

PR #21235 opened by igutidze
URL: https://code.ffmpeg.org/FFmpeg/FFmpeg/pulls/21235
Patch URL: https://code.ffmpeg.org/FFmpeg/FFmpeg/pulls/21235.patch

According to the manual, the kernel doubles requested SO_RCVBUF value set
using setsockopt and this doubled value is returned by getsockopt.

Take into account this effect when checking whether requested buffer size
has been applied.

Signed-off-by: igutidze <irakli.ghutidze@protonmail.com>


>From 92bf82522f32dc585772aaf2ef7ec284cf5fe89f Mon Sep 17 00:00:00 2001
From: igutidze <irakli.ghutidze@protonmail.com>
Date: Thu, 18 Dec 2025 18:36:51 +0000
Subject: [PATCH] udp.c: take into account doubling of SO_RCVBUF size

According to the manual, the kernel doubles requested SO_RCVBUF value set
using setsockopt and this doubled value is returned by getsockopt.

Take into account this effect when checking whether requested buffer size
has been applied.

Signed-off-by: igutidze <irakli.ghutidze@protonmail.com>
---
 libavformat/udp.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/libavformat/udp.c b/libavformat/udp.c
index 61e80c86c5..fe725f3b4a 100644
--- a/libavformat/udp.c
+++ b/libavformat/udp.c
@@ -879,9 +879,10 @@ static int udp_open(URLContext *h, const char *uri, int flags)
         if (getsockopt(udp_fd, SOL_SOCKET, SO_RCVBUF, &tmp, &len) < 0) {
             ff_log_net_error(h, AV_LOG_WARNING, "getsockopt(SO_RCVBUF)");
         } else {
-            av_log(h, AV_LOG_DEBUG, "end receive buffer size reported is %d\n", tmp);
-            if(tmp < s->buffer_size)
-                av_log(h, AV_LOG_WARNING, "attempted to set receive buffer to size %d but it only ended up set as %d\n", s->buffer_size, tmp);
+            /* setsockopt doubles requested value, getsockopt returns the doubled value */
+            av_log(h, AV_LOG_DEBUG, "end receive buffer size reported is %d\n", tmp / 2);
+            if(tmp / 2 < s->buffer_size)
+                av_log(h, AV_LOG_WARNING, "attempted to set receive buffer to size %d but it only ended up set as %d\n", s->buffer_size, tmp / 2);
         }
 
         /* make the socket non-blocking */
-- 
2.49.1

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