linux-kernel - Re: [PATCH 1/3] tty: n_gsm: add ioctl for DLC specific parameter configuration

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Date:   Tue, 28 Feb 2023 07:58:48 +0100
From:   Jiri Slaby <jirislaby@...nel.org>
To:     "D. Starke" <daniel.starke@...mens.com>,
        linux-serial@...r.kernel.org, gregkh@...uxfoundation.org,
        ilpo.jarvinen@...ux.intel.com
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] tty: n_gsm: add ioctl for DLC specific parameter
 configuration

On 28. 02. 23, 7:29, D. Starke wrote:
> From: Daniel Starke <daniel.starke@...mens.com>
> 
> Parameter negotiation has been introduced with
> commit 92f1f0c3290d ("tty: n_gsm: add parameter negotiation support")
> 
> However, means to set individual parameters per DLCI are not yet
> implemented. Furthermore, it is currently not possible to keep a DLCI half
> open until the user application sets the right parameters for it. This is
> required to allow a user application to set its specific parameters before
> the underlying link is established. Otherwise, the link is opened and
> re-established right afterwards if the user application sets incompatible
> parameters. This may be an unexpected behavior for the peer.
> 
> Add parameter 'wait_config' to 'gsm_config' to support setups where the
> DLCI specific user application sets its specific parameters after open()
> and before the link gets fully established. Setting this to zero disables
> the user application specific DLCI configuration option.
> 
> Add the ioctls 'GSMIOC_GETCONF_DLCI' and 'GSMIOC_SETCONF_DLCI' for the
> ldisc and virtual ttys. This gets/sets the DLCI specific parameters and may
> trigger a reconnect of the DLCI if incompatible values have been set. Only
> the parameters for the DLCI associated with the virtual tty can be set or
> retrieved if called on these.
> 
> Add remark within the documentation to introduce the new ioctls.
> 
> Signed-off-by: Daniel Starke <daniel.starke@...mens.com>
...
> @@ -2453,6 +2476,128 @@ static void gsm_kick_timer(struct timer_list *t)
>   		pr_info("%s TX queue stalled\n", __func__);
>   }
>   
> +/**
> + * gsm_dlci_copy_config_values	-	copy DLCI configuration
> + * @dlci: source DLCI
> + * @dc: configuration structure to fill
> + */
> +static void gsm_dlci_copy_config_values(struct gsm_dlci *dlci, struct gsm_dlci_config *dc)
> +{
> +	memset(dc, 0, sizeof(*dc));
> +	dc->channel = (u32)dlci->addr;
> +	dc->adaption = (u32)dlci->adaption;
> +	dc->mtu = (u32)dlci->mtu;
> +	dc->priority = (u32)dlci->prio;
> +	if (dlci->ftype == UIH)
> +		dc->i = 1;
> +	else
> +		dc->i = 2;
> +	dc->k = (u32)dlci->k;

Why all those casts?

> +}
> +
> +/**
> + * gsm_dlci_config	-	configure DLCI from configuration
> + * @dlci: DLCI to configure
> + * @dc: DLCI configuration
> + * @open: open DLCI after configuration?
> + */
> +static int gsm_dlci_config(struct gsm_dlci *dlci, struct gsm_dlci_config *dc, int open)
> +{
> +	struct gsm_mux *gsm;
> +	bool need_restart = false;
> +	bool need_open = false;
> +	unsigned int i;
> +
> +	/*
> +	 * Check that userspace doesn't put stuff in here to prevent breakages
> +	 * in the future.
> +	 */
> +	for (i = 0; i < ARRAY_SIZE(dc->reserved); i++)
> +		if (dc->reserved[i])
> +			return -EINVAL;
> +
> +	if (!dlci)
> +		return -EINVAL;
> +	gsm = dlci->gsm;
> +
> +	/* Stuff we don't support yet - I frame transport */
> +	if (dc->adaption != 1 && dc->adaption != 2)
> +		return -EOPNOTSUPP;
> +	if (dc->mtu > MAX_MTU || dc->mtu < MIN_MTU || (unsigned int)dc->mtu > gsm->mru)
> +		return -EINVAL;
> +	if (dc->priority >= 64)
> +		return -EINVAL;
> +	if (dc->i == 0 || dc->i > 2)  /* UIH and UI only */
> +		return -EINVAL;
> +	if (dc->k > 7)
> +		return -EINVAL;
> +
> +	/*
> +	 * See what is needed for reconfiguration
> +	 */
> +	/* Framing fields */
> +	if ((int)dc->adaption != dlci->adaption)
> +		need_restart = true;
> +	if ((unsigned int)dc->mtu != dlci->mtu)
> +		need_restart = true;
> +	if ((u8)dc->i != dlci->ftype)
> +		need_restart = true;
> +	/* Requires care */
> +	if ((u8)dc->priority != (u32)dlci->prio)
> +		need_restart = true;

And here.

> +
> +	if ((open && gsm->wait_config) || need_restart)
> +		need_open = true;
> +	if (dlci->state == DLCI_WAITING_CONFIG) {
> +		need_restart = false;
> +		need_open = true;
> +	}
> +
> +	/*
> +	 * Close down what is needed, restart and initiate the new
> +	 * configuration.
> +	 */
> +	if (need_restart) {
> +		gsm_dlci_begin_close(dlci);
> +		wait_event_interruptible(gsm->event, dlci->state == DLCI_CLOSED);
> +		if (signal_pending(current))
> +			return -EINTR;
> +	}
> +	/*
> +	 * Setup the new configuration values
> +	 */
> +	dlci->adaption = (int)dc->adaption;
> +
> +	if (dlci->mtu)

dc->mtu?

> +		dlci->mtu = (unsigned int)dc->mtu;
> +	else
> +		dlci->mtu = gsm->mtu;
> +
> +	if (dc->priority)
> +		dlci->prio = (u8)dc->priority;
> +	else
> +		dlci->prio = roundup(dlci->addr + 1, 8) - 1;
> +
> +	if (dc->i == 1)
> +		dlci->ftype = UIH;
> +	else if (dc->i == 2)
> +		dlci->ftype = UI;
> +
> +	if (dc->k)
> +		dlci->k = (u8)dc->k;
> +	else
> +		dlci->k = gsm->k;
> +
> +	if (need_open) {
> +		if (gsm->initiator)
> +			gsm_dlci_begin_open(dlci);
> +		else
> +			gsm_dlci_set_opening(dlci);
> +	}
> +
> +	return 0;
> +}
> +
>   /*
>    *	Allocate/Free DLCI channels
>    */

-- 
js
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