[newlib-cygwin] Cygwin: termios: Trim buffer size for GetConsoleProcessList()

[Takashi Yano]

https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=1a49c17840660bc0e493b7db2d9ce5289906049d

commit 1a49c17840660bc0e493b7db2d9ce5289906049d
Author: Takashi Yano <takashi.yano@nifty.ne.jp>
Date:   Wed Dec 4 13:00:39 2024 +0900

    Cygwin: termios: Trim buffer size for GetConsoleProcessList()
    
    Currently, the buffer of 128KB is passed to GetConsoleProcessList().
    This causes page fault in the select() loop for console due to:
    https://github.com/microsoft/terminal/issues/18264
    because the previous code calls GetConsoleProcessList() with large
    buffer and PeekConsoleInput() with small buffer alternately.
    With this patch, the minimum buffer size is used that is determined
    by GetConsoleProcessList() with small buffer passed.
    
    Addresses: https://cygwin.com/pipermail/cygwin/2024-December/256841.html
    Fixes: 72770148ad0a ("Cygwin: pty: Prevent pty from changing code page of parent console.")
    Reported-by: Steven Buehler <buehlersj@outlook.com>
    Signed-off-by: Takashi Yano <takashi.yano@nifty.ne.jp>

Diff:
---
 winsup/cygwin/fhandler/termios.cc | 14 ++++++++++++--
 winsup/cygwin/release/3.5.5       |  3 +++
 2 files changed, 15 insertions(+), 2 deletions(-)

diff --git a/winsup/cygwin/fhandler/termios.cc b/winsup/cygwin/fhandler/termios.cc
index 585e6ac4a..3cbdf7fca 100644
--- a/winsup/cygwin/fhandler/termios.cc
+++ b/winsup/cygwin/fhandler/termios.cc
@@ -870,8 +870,18 @@ fhandler_termios::get_console_process_id (DWORD pid, bool match,
   DWORD *list = (DWORD *) tp.c_get ();
   const DWORD buf_size = NT_MAX_PATH / sizeof (DWORD);
 
-  DWORD num = GetConsoleProcessList (list, buf_size);
-  if (num == 0 || num > buf_size)
+  DWORD buf_size1 = 1;
+  DWORD num;
+  /* The buffer of too large size does not seem to be expected by new condrv.
+     https://github.com/microsoft/terminal/issues/18264#issuecomment-2515448548
+     Use the minimum buffer size in the loop. */
+  while ((num = GetConsoleProcessList (list, buf_size1)) > buf_size1)
+    {
+      if (num > buf_size)
+	return 0;
+      buf_size1 = num;
+    }
+  if (num == 0)
     return 0;
 
   DWORD res_pri = 0, res = 0;
diff --git a/winsup/cygwin/release/3.5.5 b/winsup/cygwin/release/3.5.5
index d41d168c6..7ccf28abf 100644
--- a/winsup/cygwin/release/3.5.5
+++ b/winsup/cygwin/release/3.5.5
@@ -48,3 +48,6 @@ Fixes:
 
 - sched_setscheduler(2) allows to change the priority if the policy is
   equal to the value returned by sched_getscheduler(2).
+
+- Fix frequent page fault caused in Windows Terminal.
+  Addresses: https://cygwin.com/pipermail/cygwin/2024-December/256841.html