Hi René,
On Wed, 10 Aug 2022, René Scharfe wrote:
> write() on Windows reports ENOSPC when writing to a non-blocking pipe
> whose buffer is full and rejects writes bigger than the buffer outright.
> Change the error code to EAGAIN and try a buffer-sized partial write to
> comply with POSIX and the expections of our Git-internal callers.
Excellent analysis, thank you!
However, let's reword this to clarify that the error code is set to EAGAIN
only if the buffer-sized partial write fails.
>
> Helped-by: Jeff King <peff@xxxxxxxx>
> Signed-off-by: René Scharfe <l.s.r@xxxxxx>
> ---
> compat/mingw.c | 19 ++++++++++++++++++-
> 1 file changed, 18 insertions(+), 1 deletion(-)
>
> diff --git a/compat/mingw.c b/compat/mingw.c
> index b5502997e2..c6f244c0fe 100644
> --- a/compat/mingw.c
> +++ b/compat/mingw.c
> @@ -689,6 +689,8 @@ int mingw_fflush(FILE *stream)
> return ret;
> }
>
> +#define PIPE_BUFFER_SIZE (8192)
This constant hails all the way back from 897bb8cb2c2 (Windows: A pipe()
replacement whose ends are not inherited to children., 2007-12-07), in
case anyone wondered like I did where that number came from (and why it is
so low).
It is outside the purview of this patch to change that constant, therefore
I am fine with leaving this as-is.
> +
> #undef write
> ssize_t mingw_write(int fd, const void *buf, size_t len)
> {
> @@ -702,6 +704,21 @@ ssize_t mingw_write(int fd, const void *buf, size_t len)
> else
> errno = EINVAL;
> }
> + if (result < 0 && errno == ENOSPC) {
It might make the code clearer to turn this into an `else if`.
> + /* check if fd is a non-blocking pipe */
> + HANDLE h = (HANDLE) _get_osfhandle(fd);
> + DWORD s;
> + if (GetFileType(h) == FILE_TYPE_PIPE &&
> + GetNamedPipeHandleState(h, &s, NULL, NULL, NULL, NULL, 0) &&
> + (s & PIPE_NOWAIT)) {
> + DWORD obuflen;
> + if (!GetNamedPipeInfo(h, NULL, &obuflen, NULL, NULL))
> + obuflen = PIPE_BUFFER_SIZE;
> + if (len > obuflen)
> + return mingw_write(fd, buf, obuflen);
It is probably easier to reason about to recurse instead of using a `goto`
here.
Thank you for this patch!
Dscho
> + errno = EAGAIN;
> + }
> + }
>
> return result;
> }
> @@ -1079,7 +1096,7 @@ int pipe(int filedes[2])
> HANDLE h[2];
>
> /* this creates non-inheritable handles */
> - if (!CreatePipe(&h[0], &h[1], NULL, 8192)) {
> + if (!CreatePipe(&h[0], &h[1], NULL, PIPE_BUFFER_SIZE)) {
> errno = err_win_to_posix(GetLastError());
> return -1;
> }
> --
> 2.37.1.windows.1
>
