Re: Bug#1003095: /usr/bin/script: hangs when child doesn't read input fast enough

[Karel Zak <kzak@redhat.com>]

On Fri, Jan 14, 2022 at 12:28:11AM +0100, наб wrote:
> -static int write_to_child(struct ul_pty *pty, char *buf, size_t bufsz)
> +static int schedule_child_write(struct ul_pty *pty, char *buf, size_t bufsz, int final)
>  {
> -	return write_all(pty->master, buf, bufsz);
> +	struct ul_pty_child_buffer *stash = calloc(1, sizeof(*stash));

It means that for each activity on the file descriptor it will
allocate a new buffer (in BUFSIZ). It seems pretty expensive.

Cannot we reuse the buffers? 

Maybe use include/list.h, define two lists, one for not-yet-written 
buffers and another for ready-to-use buffers and move from one list to
another in schedule_child_write() and flush_child_buffers().

> +	if (!stash)
> +		return -1;
> +
> +	memcpy(stash->buf, buf, bufsz);
> +	stash->size = bufsz;
> +	stash->final_input = final ? 1 : 0;
> +
> +	if (pty->child_buffer_head)
> +		pty->child_buffer_tail = pty->child_buffer_tail->next = stash;
> +	else
> +		pty->child_buffer_head = pty->child_buffer_tail = stash;
> +	return 0;
>  }
>  
>  /*
> @@ -311,16 +329,13 @@ static int write_to_child(struct ul_pty
>   * maintains master+slave tty stuff within the session. Use pipe to write to
>   * pty and assume non-interactive (tee-like) behavior is NOT well supported.
>   */
> -void ul_pty_write_eof_to_child(struct ul_pty *pty)
> +static void drain(struct ul_pty *pty)

drain_child_buffers() :-)


Anyway, it looks good.

    Karel



-- 
 Karel Zak  <kzak@redhat.com>
 http://karelzak.blogspot.com