Re: [Minios-devel] [PATCH] mini-os: Remove \r\n conversion when writing to PV serial port

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Wed, May 10, 2017 at 11:33:23PM +0100, Simon Waterman wrote:
> This change removes \n to \r\n conversion when writing to a PV serial
> port so that binary protocols carried over the port are not corrupted.
> 
> The change enables new use-cases for example connectivity from the Windows
> Kernel Debugger to a guest via it's IOEMU stubdom.
> 
> Signed-off-by: Simon Waterman <watermansrdev@xxxxxxxxx>
> ---

Actually, from a conversation on #xendevel:

<Diziet> I think a serial port (and therefore by extension a console)
contains something roughly like a terminal would expect (eg, something
like a telnet NVT bytestream).
<Diziet> All other UNIXish operating systems turn  printf("\n")  into
\r\n.
<Diziet> Normally they do this in the tty driver.

<Diziet> Then if the guest sends just \n, you will get staircase output.
<Diziet> Obviously the Xen PV console protocol can be used for other
things besides being an actual console.
<Diziet> But if that is desired, the line ending conversion should be
moved to something related to consoleness in the guest (ie in minios),
not just deleted.

I think Ian explained why it was done like that.

We should probably move this somewhere else.

Simon, can you clarify your use case? Doesn't this patch cause xl
console to print out staircase output?

>  console/console.c | 29 +----------------------------
>  1 file changed, 1 insertion(+), 28 deletions(-)
> 
> diff --git a/console/console.c b/console/console.c
> index 5538bd4..de94ad6 100644
> --- a/console/console.c
> +++ b/console/console.c
> @@ -82,10 +82,6 @@ void xencons_tx(void)
>  
>  void console_print(struct consfront_dev *dev, char *data, int length)
>  {
> -    char *curr_char, saved_char;
> -    char copied_str[length+1];
> -    char *copied_ptr;
> -    int part_len;
>      int (*ring_send_fn)(struct consfront_dev *dev, const char *data, 
> unsigned length);
>  
>      if(!console_initialised)
> @@ -93,30 +89,7 @@ void console_print(struct consfront_dev *dev, char *data, 
> int length)
>      else
>          ring_send_fn = xencons_ring_send;
>  
> -    copied_ptr = copied_str;
> -    memcpy(copied_ptr, data, length);
> -    for(curr_char = copied_ptr; curr_char < copied_ptr+length-1; curr_char++)
> -    {
> -        if(*curr_char == '\n')
> -        {
> -            *curr_char = '\r';
> -            saved_char = *(curr_char+1);
> -            *(curr_char+1) = '\n';
> -            part_len = curr_char - copied_ptr + 2;
> -            ring_send_fn(dev, copied_ptr, part_len);
> -            *(curr_char+1) = saved_char;
> -            copied_ptr = curr_char+1;
> -            length -= part_len - 1;
> -        }
> -    }
> -
> -    if (copied_ptr[length-1] == '\n') {
> -        copied_ptr[length-1] = '\r';
> -        copied_ptr[length] = '\n';
> -        length++;
> -    }
> -    
> -    ring_send_fn(dev, copied_ptr, length);
> +    ring_send_fn(dev, data, length);
>  }
>  
>  void print(int direct, const char *fmt, va_list args)
> -- 
> 2.7.4
> 

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