From c1300397f86a397ae38ad08126dc8e021067f128 Mon Sep 17 00:00:00 2001
From: Dmitry Gutov <dmitry@gutov.dev>
Date: Sun, 24 Sep 2023 01:29:18 +0300
Subject: [PATCH 3/3] Dynamically increase the readmax if the pipe has more
 available

* src/process.c (read_process_output): Dynamically increase the
buffer size depending on the pipe's buffered contents (bug#66020).
---
 src/process.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/src/process.c b/src/process.c
index d7aedcdf12d..13cf6d6c50d 100644
--- a/src/process.c
+++ b/src/process.c
@@ -6146,6 +6146,17 @@ read_process_output (Lisp_Object proc, int channel)
   Lisp_Object odeactivate;
   char *chars;
 
+#ifdef USABLE_FIONREAD
+#ifdef DATAGRAM_SOCKETS
+  if (!DATAGRAM_CHAN_P (channel))
+#endif
+    {
+      int available_read;
+      ioctl (p->infd, FIONREAD, &available_read);
+      readmax = MAX (readmax, available_read);
+    }
+#endif
+
   USE_SAFE_ALLOCA;
   chars = SAFE_ALLOCA (sizeof coding->carryover + readmax);
 
-- 
2.37.2