linux-kernel - Re: [PATCH V2 2/2] rpmsg: add syslog redirection driver

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Date:   Thu, 14 Feb 2019 15:09:40 +0200
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Xiang Xiao <xiaoxiang781216@...il.com>
Cc:     rdunlap@...radead.org, gregkh@...uxfoundation.org,
        alexander.shishkin@...ux.intel.com, ohad@...ery.com,
        bjorn.andersson@...aro.org, wendy.liang@...inx.com,
        arnaud.pouliquen@...com, kumar.gala@...aro.org,
        linux-remoteproc@...r.kernel.org, linux-kernel@...r.kernel.org,
        Guiding Li <liguiding@...econe.net>
Subject: Re: [PATCH V2 2/2] rpmsg: add syslog redirection driver

On Thu, Feb 14, 2019 at 02:02:38PM +0800, Xiang Xiao wrote:
> From: Guiding Li <liguiding@...econe.net>
> 
> This driver allows the remote processor to redirect the output of
> syslog or printf into the kernel log, which is very useful to see
> what happen in the remote side.

> +struct rpmsg_syslog_header {
> +	u32				command;
> +	s32				result;
> +} __packed;

Isn't packed already?

> +struct rpmsg_syslog_transfer {
> +	struct rpmsg_syslog_header	header;
> +	u32				count;
> +	char				data[0];
> +} __packed;

Ditto.

> +static int rpmsg_syslog_callback(struct rpmsg_device *rpdev,
> +				 void *data, int len, void *priv_, u32 src)
> +{
> +	struct rpmsg_syslog *priv = dev_get_drvdata(&rpdev->dev);
> +	struct rpmsg_syslog_transfer *msg = data;
> +	struct rpmsg_syslog_transfer_done done;
> +	unsigned int copied = msg->count;
> +	unsigned int printed = 0;
> +	const char *nl;
> +
> +	if (msg->header.command != RPMSG_SYSLOG_TRANSFER)
> +		return -EINVAL;
> +
> +	/* output the message before '\n' to the kernel log */
> +	nl = memrchr(msg->data, '\n', msg->count);

Hmm... To me it sounds somehow fragile.

If your text contains binary data, how can you guarantee that it would be not
in the middle of two \n:s? OTOH, if it text data, why do you need to take all
strings at once? It might be worse from performance prospective (if you know
how and when printk() supplies buffer to the console).

> +	if (nl) {
> +		printed = nl + 1 - msg->data;
> +		copied = msg->count - printed;
> +
> +		if (priv->next) {
> +			pr_info("%.*s%.*s", priv->next,
> +				priv->buf, printed, msg->data);
> +			priv->next = 0;
> +		} else {
> +			pr_info("%.*s", printed, msg->data);
> +		}
> +	}
> +
> +	/* append the message after '\n' to the buffer */

> +	if (copied != 0) {



> +		unsigned int newsize = priv->next + copied;
> +
> +		if (newsize > priv->size) {
> +			char *newbuf;
> +
> +			newbuf = krealloc(priv->buf, newsize, GFP_KERNEL);
> +			if (newbuf) {
> +				priv->buf  = newbuf;
> +				priv->size = newsize;
> +			} else {
> +				copied = priv->size - priv->next;
> +			}
> +		}
> +

> +		strncpy(priv->buf + priv->next, msg->data + printed, copied);

Hmm... shouldn't be memcpy()?

> +		priv->next += copied;
> +	}
> +
> +	done.command = RPMSG_SYSLOG_TRANSFER_DONE;
> +	done.result  = printed + copied;
> +	return rpmsg_send(rpdev->ept, &done, sizeof(done));
> +}
> +
> +static int rpmsg_syslog_probe(struct rpmsg_device *rpdev)
> +{
> +	struct rpmsg_syslog *priv;
> +
> +	priv = devm_kzalloc(&rpdev->dev, sizeof(*priv), GFP_KERNEL);
> +	if (!priv)
> +		return -ENOMEM;
> +
> +	dev_set_drvdata(&rpdev->dev, priv);
> +	return 0;
> +}
> +
> +static void rpmsg_syslog_remove(struct rpmsg_device *rpdev)
> +{
> +	struct rpmsg_syslog *priv = dev_get_drvdata(&rpdev->dev);
> +

> +	/* flush the buffered log if need */
> +	if (priv->next)
> +		pr_info("%.*s\n", priv->next, priv->buf);
> +	kfree(priv->buf);

I don't see how it's serialized. Does rpmsg core take care of this?

> +}

> +#ifdef CONFIG_PM_SLEEP

You can consider to use __maybe_unused annotation to the below function.

> +static int rpmsg_syslog_dev_suspend(struct device *dev)
> +{

> +}
> +
> +static int rpmsg_syslog_dev_resume(struct device *dev)
> +{

> +}
> +#endif

> +static const struct rpmsg_device_id rpmsg_syslog_id_table[] = {
> +	{ .name = "rpmsg-syslog" },
> +	{ },

Terminator better without comma.

> +};

-- 
With Best Regards,
Andy Shevchenko