[PATCH v2 0/1] MR10199: msvcrt: Fix no buffering detection in _fwrite_nolock().

[Paul Gofman (＠gofman)]

--
  v2: msvcrt: Fix no buffering detection in _fwrite_nolock().
 
https://gitlab.winehq.org/wine/wine/-/merge_requests/10199

[PATCH v2 1/1] msvcrt: Fix no buffering detection in _fwrite_nolock().

[Paul Gofman]

From: Paul Gofman <[e-mail]>

---
 dlls/msvcrt/file.c | 21 +++++++--------------
 1 file changed, 7 insertions(+), 14 deletions(-)

diff --git a/dlls/msvcrt/file.c b/dlls/msvcrt/file.c
index 01853625c23..d999996e7d6 100644
--- a/dlls/msvcrt/file.c
+++ b/dlls/msvcrt/file.c
@@ -4147,10 +4147,14 @@ size_t CDECL fwrite(const void *ptr, size_t size, size_t nmemb, FILE* file)
 size_t CDECL _fwrite_nolock(const void *ptr, size_t size, size_t nmemb, FILE* file)
 {
     size_t wrcnt=size * nmemb;
-    int written = 0;
+    int written = 0, bufsize = 1;
     if (size == 0)
         return 0;
 
+    if (((file->_flag & (MSVCRT__NOBUF | _IOMYBUF | MSVCRT__USERBUF)) || msvcrt_alloc_buffer(file))
+            && (file->_flag & (_IOMYBUF | MSVCRT__USERBUF)))
+        bufsize = file->_bufsiz;
+
     while(wrcnt) {
         if(file->_cnt < 0) {
             WARN("negative file->_cnt value in %p\n", file);
@@ -4164,20 +4168,9 @@ size_t CDECL _fwrite_nolock(const void *ptr, size_t size, size_t nmemb, FILE* fi
             written += pcnt;
             wrcnt -= pcnt;
             ptr = (const char*)ptr + pcnt;
-        } else if((file->_flag & MSVCRT__NOBUF)
-                || ((file->_flag & (_IOMYBUF | MSVCRT__USERBUF)) && wrcnt >= file->_bufsiz)
-                || (!(file->_flag & (_IOMYBUF | MSVCRT__USERBUF)) && wrcnt >= MSVCRT_INTERNAL_BUFSIZ)) {
+        } else if(wrcnt >= bufsize) {
             size_t pcnt;
-            int bufsiz;
-
-            if(file->_flag & MSVCRT__NOBUF)
-                bufsiz = 1;
-            else if(!(file->_flag & (_IOMYBUF | MSVCRT__USERBUF)))
-                bufsiz = MSVCRT_INTERNAL_BUFSIZ;
-            else
-                bufsiz = file->_bufsiz;
-
-            pcnt = (wrcnt / bufsiz) * bufsiz;
+            pcnt = (wrcnt / bufsize) * bufsize;
 
             if(msvcrt_flush_buffer(file) == EOF)
                 break;
-- 
GitLab

https://gitlab.winehq.org/wine/wine/-/merge_requests/10199

[Paul Gofman (＠gofman)]

v2:
 - simplify expressions and get bufsize before the loop.

-- 
https://gitlab.winehq.org/wine/wine/-/merge_requests/10199#note_130734

[Paul Gofman (＠gofman)]

On Fri Feb 27 16:24:33 2026 +0000, Piotr Caban wrote:
> Yes, but when it sets IOMYBUF or NOBUF (and returns TRUE) it also sets
> file-\>\_bufsiz. I don't see anything wrong in proposed change.
> Well, yes, It may in theory set _NOBUF and bufsiz to 2 and we probably still want to treat that as bufferred write instead of going byte by byte to flsbuf. I will update v2.

-- 
https://gitlab.winehq.org/wine/wine/-/merge_requests/10199#note_130735