Re: [PATCH v2 3/6] tty: n_gsm: replace use of gsm_read_ea() with gsm_read_ea_val()

[Jiri Slaby]

On 23. 08. 22, 8:22, D. Starke wrote:
> From: Daniel Starke <daniel.starke@xxxxxxxxxxx>
>
> Replace the use of gsm_read_ea() with gsm_read_ea_val() where applicable to
> improve code readability and avoid errors like in the past.

What errors?

> Reported-by: kernel test robot <lkp@xxxxxxxxx>

Perhaps you have a link?

> Signed-off-by: Daniel Starke <daniel.starke@xxxxxxxxxxx>
> ---
>   drivers/tty/n_gsm.c | 99 +++++++++++++++++++++++----------------------
>   1 file changed, 51 insertions(+), 48 deletions(-)
>
> Changes since v1:
> Fixed use of wrong variable in debug output within gsm_dlci_data().
>
> Link: https://lore.kernel.org/all/202208222147.WfFRmf1r-lkp@xxxxxxxxx/

Ah, you do. This should have been above...

> diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c
> index ed399d57b197..9535e84f3063 100644
> --- a/drivers/tty/n_gsm.c
> +++ b/drivers/tty/n_gsm.c
> @@ -1418,18 +1418,13 @@ static void gsm_control_modem(struct gsm_mux *gsm, const u8 *data, int clen)
>   	unsigned int modem = 0;
>   	struct gsm_dlci *dlci;
>   	int len = clen;
> -	int slen;
> +	int cl = clen;
>   	const u8 *dp = data;
>   	struct tty_struct *tty;
>   
> -	while (gsm_read_ea(&addr, *dp++) == 0) {
> -		len--;
> -		if (len == 0)
> -			return;
> -	}
> -	/* Must be at least one byte following the EA */
> -	len--;
> -	if (len <= 0)
> +	len = gsm_read_ea_val(&addr, data, cl);
> +

There should be likely no extra \n here between assignment and check of 
the value (len).

> +	if (len < 1)
>   		return;
>   
>   	addr >>= 1;
> @@ -1438,15 +1433,21 @@ static void gsm_control_modem(struct gsm_mux *gsm, const u8 *data, int clen)
>   		return;
>   	dlci = gsm->dlci[addr];
>   
> -	slen = len;
> -	while (gsm_read_ea(&modem, *dp++) == 0) {
> -		len--;
> -		if (len == 0)
> -			return;
> -	}
> -	len--;
> +	/* Must be at least one byte following the EA */
> +	if ((cl - len) < 1)
> +		return;
> +
> +	dp += len;
> +	cl -= len;
> +
> +	/* get the modem status */
> +	len = gsm_read_ea_val(&modem, dp, cl);
> +
> +	if (len < 1)

The same here.

> +		return;
> +
>   	tty = tty_port_tty_get(&dlci->port);
> -	gsm_process_modem(tty, dlci, modem, slen - len);
> +	gsm_process_modem(tty, dlci, modem, cl);
>   	if (tty) {
>   		tty_wakeup(tty);
>   		tty_kref_put(tty);
> @@ -1921,11 +1922,10 @@ static void gsm_dlci_data(struct gsm_dlci *dlci, const u8 *data, int clen)
>   	struct tty_port *port = &dlci->port;
>   	struct tty_struct *tty;
>   	unsigned int modem = 0;
> -	int len = clen;
> -	int slen = 0;
> +	int len;
>   
>   	if (debug & 16)
> -		pr_debug("%d bytes for tty\n", len);
> +		pr_debug("%d bytes for tty\n", clen);
>   	switch (dlci->adaption)  {
>   	/* Unsupported types */
>   	case 4:		/* Packetised interruptible data */
> @@ -1933,24 +1933,22 @@ static void gsm_dlci_data(struct gsm_dlci *dlci, const u8 *data, int clen)
>   	case 3:		/* Packetised uininterruptible voice/data */
>   		break;
>   	case 2:		/* Asynchronous serial with line state in each frame */
> -		while (gsm_read_ea(&modem, *data++) == 0) {
> -			len--;
> -			slen++;
> -			if (len == 0)
> -				return;
> -		}
> -		len--;
> -		slen++;
> +		len = gsm_read_ea_val(&modem, data, clen);
> +		if (len < 1)
> +			return;
>   		tty = tty_port_tty_get(port);
>   		if (tty) {
> -			gsm_process_modem(tty, dlci, modem, slen);
> +			gsm_process_modem(tty, dlci, modem, len);
>   			tty_wakeup(tty);
>   			tty_kref_put(tty);
>   		}
> +		/* Skip processed modem data */
> +		data += len;
> +		clen -= len;
>   		fallthrough;
>   	case 1:		/* Line state will go via DLCI 0 controls only */
>   	default:
> -		tty_insert_flip_string(port, data, len);
> +		tty_insert_flip_string(port, data, clen);
>   		tty_flip_buffer_push(port);
>   	}
>   }
> @@ -1971,24 +1969,29 @@ static void gsm_dlci_command(struct gsm_dlci *dlci, const u8 *data, int len)
>   {
>   	/* See what command is involved */
>   	unsigned int command = 0;
> -	while (len-- > 0) {
> -		if (gsm_read_ea(&command, *data++) == 1) {
> -			int clen = *data++;
> -			len--;
> -			/* FIXME: this is properly an EA */
> -			clen >>= 1;
> -			/* Malformed command ? */
> -			if (clen > len)
> -				return;
> -			if (command & 1)
> -				gsm_control_message(dlci->gsm, command,
> -								data, clen);
> -			else
> -				gsm_control_response(dlci->gsm, command,
> -								data, clen);
> -			return;
> -		}
> -	}
> +	const u8 *dp = data;

Why is the local "dp" needed?

> +	int clen = 0;
> +	int dlen;

Having lengths signed is mostly confusing. Shouldn't/couldn't they be 
uint instead?

> +	/* read the command */
> +	dlen = gsm_read_ea_val(&command, dp, len);
> +	len -= dlen;
> +	dp += dlen;
> +
> +	/* read any control data */
> +	dlen = gsm_read_ea_val(&clen, dp, len);
> +	len -= dlen;
> +	dp += dlen;
> +
> +	/* Malformed command? */
> +	if (clen > len)
> +		return;
> +
> +	if (command & 1)
> +		gsm_control_message(dlci->gsm, command, dp, clen);
> +	else
> +		gsm_control_response(dlci->gsm, command, dp, clen);
> +	return;

An extra return.

>   }

thanks,
--
js
suse labs