linux-kernel - Re: [PATCH v2 1/2] tty: Convert tty

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Message-ID: <Y2Mtricfx/HxiEHc@kroah.com>
Date:   Thu, 3 Nov 2022 03:55:42 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
Cc:     linux-serial@...r.kernel.org, Jiri Slaby <jirislaby@...nel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/2] tty: Convert tty_buffer flags to bool

On Wed, Oct 19, 2022 at 01:55:03PM +0300, Ilpo Järvinen wrote:
> The struct tty_buffer has flags which is only used for storing TTYB_NORMAL.
> There is also a few quite confusing operations for checking the presense
> of TTYB_NORMAL. Simplify things by converting flags to bool.
> 
> Despite the name remaining the same, the meaning of "flags" is altered
> slightly by this change. Previously it referred to flags of the buffer
> (only TTYB_NORMAL being used as a flag). After this change, flags tell
> whether the buffer contains/should be allocated with flags array along
> with character data array. It is much more suitable name that
> TTYB_NORMAL was for this purpose, thus the name remains.
> 
> Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
> ---
> 
> v2:
> - Make it more obvious why flags is not renamed (both in kerneldoc
>   comment and commit message).
> 
>  drivers/tty/tty_buffer.c   | 28 ++++++++++++++--------------
>  include/linux/tty_buffer.h |  5 +----
>  include/linux/tty_flip.h   |  4 ++--
>  3 files changed, 17 insertions(+), 20 deletions(-)
> 
> diff --git a/drivers/tty/tty_buffer.c b/drivers/tty/tty_buffer.c
> index 5e287dedce01..b408d830fcbc 100644
> --- a/drivers/tty/tty_buffer.c
> +++ b/drivers/tty/tty_buffer.c
> @@ -107,7 +107,7 @@ static void tty_buffer_reset(struct tty_buffer *p, size_t size)
>  	p->commit = 0;
>  	p->lookahead = 0;
>  	p->read = 0;
> -	p->flags = 0;
> +	p->flags = true;
>  }
>  
>  /**
> @@ -249,7 +249,7 @@ void tty_buffer_flush(struct tty_struct *tty, struct tty_ldisc *ld)
>   * __tty_buffer_request_room	-	grow tty buffer if needed
>   * @port: tty port
>   * @size: size desired
> - * @flags: buffer flags if new buffer allocated (default = 0)
> + * @flags: buffer has to store flags along character data
>   *
>   * Make at least @size bytes of linear space available for the tty buffer.
>   *
> @@ -260,19 +260,19 @@ void tty_buffer_flush(struct tty_struct *tty, struct tty_ldisc *ld)
>   * Returns: the size we managed to find.
>   */
>  static int __tty_buffer_request_room(struct tty_port *port, size_t size,
> -				     int flags)
> +				     bool flags)
>  {
>  	struct tty_bufhead *buf = &port->buf;
>  	struct tty_buffer *b, *n;
>  	int left, change;
>  
>  	b = buf->tail;
> -	if (b->flags & TTYB_NORMAL)
> +	if (!b->flags)
>  		left = 2 * b->size - b->used;
>  	else
>  		left = b->size - b->used;
>  
> -	change = (b->flags & TTYB_NORMAL) && (~flags & TTYB_NORMAL);
> +	change = !b->flags && flags;
>  	if (change || left < size) {
>  		/* This is the slow path - looking for new buffers to use */
>  		n = tty_buffer_alloc(port, size);
> @@ -300,7 +300,7 @@ static int __tty_buffer_request_room(struct tty_port *port, size_t size,
>  
>  int tty_buffer_request_room(struct tty_port *port, size_t size)
>  {
> -	return __tty_buffer_request_room(port, size, 0);
> +	return __tty_buffer_request_room(port, size, true);

Did this logic just get inverted?

Maybe it's the jet-lag, but this feels like it's not correct anymore.

Maybe a commet up above where you calculate "left" would make more sense
as to what is going on?

thanks,

greg k-h