[PATCH V2 1/2] lib/string: add memrchr function

[PATCH V2 1/2] lib/string: add memrchr function

[Xiang Xiao]

Here is the detailed description for memrchr:

void *memrchr(const void *s, int c, size_t n);

The memrchr() function is like the memchr() function, except
that it searches backward from the end of the n bytes pointed
to by s instead of forward from the beginning.

The memrchr() functions return a pointer to the matching byte
or NULL if the character does not occur in the given memory
area.

Signed-off-by: Xiang Xiao <xiaoxiang@xiaomi.com>
---
 include/linux/string.h |  3 +++
 lib/string.c           | 23 +++++++++++++++++++++++
 2 files changed, 26 insertions(+)

diff --git a/include/linux/string.h b/include/linux/string.h
index 7927b87..915c617 100644
--- a/include/linux/string.h
+++ b/include/linux/string.h
@@ -167,6 +167,9 @@ static inline void memcpy_flushcache(void *dst, const void *src, size_t cnt)
 	memcpy(dst, src, cnt);
 }
 #endif
+#ifndef __HAVE_ARCH_MEMRCHR
+void *memrchr(const void *s, int c, size_t n);
+#endif
 void *memchr_inv(const void *s, int c, size_t n);
 char *strreplace(char *s, char old, char new);
 
diff --git a/lib/string.c b/lib/string.c
index 38e4ca0..595e0b3 100644
--- a/lib/string.c
+++ b/lib/string.c
@@ -964,6 +964,29 @@ void *memchr(const void *s, int c, size_t n)
 EXPORT_SYMBOL(memchr);
 #endif
 
+#ifndef __HAVE_ARCH_MEMRCHR
+/**
+ * memrchr - Find the last character in an area of memory.
+ * @s: The memory area
+ * @c: The byte to search for
+ * @n: The size of the area.
+ *
+ * Return: the address of the last occurrence of @c, or %NULL
+ * if @c is not found
+ */
+void *memrchr(const void *s, int c, size_t n)
+{
+	const unsigned char *p = s + n;
+
+	while (n-- != 0) {
+		if ((unsigned char)c == *--p)
+			return (void *)p;
+	}
+	return NULL;
+}
+EXPORT_SYMBOL(memrchr);
+#endif
+
 static void *check_bytes8(const u8 *start, u8 value, unsigned int bytes)
 {
 	while (bytes) {
-- 
2.7.4

[PATCH V2 2/2] rpmsg: add syslog redirection driver

[Xiang Xiao]

From: Guiding Li <liguiding@pinecone.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.

Signed-off-by: Guiding Li <liguiding@pinecone.net>
---
 drivers/rpmsg/Kconfig        |  12 ++++
 drivers/rpmsg/Makefile       |   1 +
 drivers/rpmsg/rpmsg_syslog.c | 163 +++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 176 insertions(+)
 create mode 100644 drivers/rpmsg/rpmsg_syslog.c

diff --git a/drivers/rpmsg/Kconfig b/drivers/rpmsg/Kconfig
index d0322b4..13ead55 100644
--- a/drivers/rpmsg/Kconfig
+++ b/drivers/rpmsg/Kconfig
@@ -15,6 +15,18 @@ config RPMSG_CHAR
 	  in /dev. They make it possible for user-space programs to send and
 	  receive rpmsg packets.
 
+config RPMSG_SYSLOG
+	tristate "RPMSG syslog redirection"
+	depends on RPMSG
+	help
+	  Say Y here to redirect the syslog/printf from remote processor into
+	  the kernel log which is very useful to see what happened in the remote
+	  side.
+
+	  If the remote processor hangs during bootup or panics during runtime,
+	  we can even cat /sys/kernel/debug/remoteproc/remoteprocX/trace0 to
+	  get the last log which hasn't been output yet.
+
 config RPMSG_QCOM_GLINK_NATIVE
 	tristate
 	select RPMSG
diff --git a/drivers/rpmsg/Makefile b/drivers/rpmsg/Makefile
index 9aa8595..bfd22df 100644
--- a/drivers/rpmsg/Makefile
+++ b/drivers/rpmsg/Makefile
@@ -1,6 +1,7 @@
 # SPDX-License-Identifier: GPL-2.0
 obj-$(CONFIG_RPMSG)		+= rpmsg_core.o
 obj-$(CONFIG_RPMSG_CHAR)	+= rpmsg_char.o
+obj-$(CONFIG_RPMSG_SYSLOG)	+= rpmsg_syslog.o
 obj-$(CONFIG_RPMSG_QCOM_GLINK_RPM) += qcom_glink_rpm.o
 obj-$(CONFIG_RPMSG_QCOM_GLINK_NATIVE) += qcom_glink_native.o
 obj-$(CONFIG_RPMSG_QCOM_GLINK_SMEM) += qcom_glink_smem.o
diff --git a/drivers/rpmsg/rpmsg_syslog.c b/drivers/rpmsg/rpmsg_syslog.c
new file mode 100644
index 0000000..b7a0d27
--- /dev/null
+++ b/drivers/rpmsg/rpmsg_syslog.c
@@ -0,0 +1,163 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2017 Pinecone Inc.
+ *
+ * redirect syslog/printf from remote to the kernel.
+ */
+
+#include <linux/module.h>
+#include <linux/rpmsg.h>
+#include <linux/slab.h>
+
+#define RPMSG_SYSLOG_TRANSFER		0
+#define RPMSG_SYSLOG_TRANSFER_DONE	1
+#define RPMSG_SYSLOG_SUSPEND		2
+#define RPMSG_SYSLOG_RESUME		3
+
+struct rpmsg_syslog_header {
+	u32				command;
+	s32				result;
+} __packed;
+
+struct rpmsg_syslog_transfer {
+	struct rpmsg_syslog_header	header;
+	u32				count;
+	char				data[0];
+} __packed;
+
+#define rpmsg_syslog_suspend		rpmsg_syslog_header
+#define rpmsg_syslog_resume		rpmsg_syslog_header
+#define rpmsg_syslog_transfer_done	rpmsg_syslog_header
+
+struct rpmsg_syslog {
+	char				*buf;
+	unsigned int			next;
+	unsigned int			size;
+};
+
+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);
+	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);
+		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);
+}
+
+#ifdef CONFIG_PM_SLEEP
+static int rpmsg_syslog_dev_suspend(struct device *dev)
+{
+	struct rpmsg_device *rpdev = dev_get_drvdata(dev);
+	struct rpmsg_syslog_suspend msg = {
+		.command = RPMSG_SYSLOG_SUSPEND,
+	};
+
+	return rpmsg_send(rpdev->ept, &msg, sizeof(msg));
+}
+
+static int rpmsg_syslog_dev_resume(struct device *dev)
+{
+	struct rpmsg_device *rpdev = dev_get_drvdata(dev);
+	struct rpmsg_syslog_resume msg = {
+		.command = RPMSG_SYSLOG_RESUME,
+	};
+
+	return rpmsg_send(rpdev->ept, &msg, sizeof(msg));
+}
+#endif
+
+static SIMPLE_DEV_PM_OPS(rpmsg_syslog_pm,
+			rpmsg_syslog_dev_suspend,
+			rpmsg_syslog_dev_resume);
+
+static const struct rpmsg_device_id rpmsg_syslog_id_table[] = {
+	{ .name = "rpmsg-syslog" },
+	{ },
+};
+MODULE_DEVICE_TABLE(rpmsg, rpmsg_syslog_id_table);
+
+static struct rpmsg_driver rpmsg_syslog_driver = {
+	.drv = {
+		.name  = "rpmsg_syslog",
+		.owner = THIS_MODULE,
+		.pm    = &rpmsg_syslog_pm,
+	},
+
+	.id_table = rpmsg_syslog_id_table,
+	.probe    = rpmsg_syslog_probe,
+	.callback = rpmsg_syslog_callback,
+	.remove   = rpmsg_syslog_remove,
+};
+
+module_rpmsg_driver(rpmsg_syslog_driver);
+
+MODULE_ALIAS("rpmsg:rpmsg_syslog");
+MODULE_AUTHOR("Guiding Li <liguiding@pinecone.net>");
+MODULE_DESCRIPTION("rpmsg syslog redirection driver");
+MODULE_LICENSE("GPL v2");
-- 
2.7.4

Re: [PATCH V2 1/2] lib/string: add memrchr function

[Andy Shevchenko]

On Thu, Feb 14, 2019 at 02:02:37PM +0800, Xiang Xiao wrote:
> Here is the detailed description for memrchr:
> 
> void *memrchr(const void *s, int c, size_t n);
> 
> The memrchr() function is like the memchr() function, except
> that it searches backward from the end of the n bytes pointed
> to by s instead of forward from the beginning.
> 
> The memrchr() functions return a pointer to the matching byte
> or NULL if the character does not occur in the given memory
> area.

> +void *memrchr(const void *s, int c, size_t n)
> +{
> +	const unsigned char *p = s + n;
> +
> +	while (n-- != 0) {

Simple:

	while (n--) {

> +		if ((unsigned char)c == *--p)
> +			return (void *)p;
> +	}
> +	return NULL;
> +}

-- 
With Best Regards,
Andy Shevchenko

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

[Andy Shevchenko]

On Thu, Feb 14, 2019 at 02:02:38PM +0800, Xiang Xiao wrote:
> From: Guiding Li <liguiding@pinecone.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

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

[Andy Shevchenko]

On Thu, Feb 14, 2019 at 03:09:40PM +0200, Andy Shevchenko wrote:
> On Thu, Feb 14, 2019 at 02:02:38PM +0800, Xiang Xiao wrote:

> > +	/* append the message after '\n' to the buffer */
> 
> > +	if (copied != 0) {

Missed comment

if (copied)

> > +	}

-- 
With Best Regards,
Andy Shevchenko

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

[xiang xiao]

On Thu, Feb 14, 2019 at 9:09 PM Andy Shevchenko
<andriy.shevchenko@linux.intel.com> wrote:
>
> On Thu, Feb 14, 2019 at 02:02:38PM +0800, Xiang Xiao wrote:
> > From: Guiding Li <liguiding@pinecone.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?
>

But, I want to make it more explicitly and prepare for struct expansion later.

> > +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?

This driver is just for log/printf redirection, so we could safely
assume the data is pure text.
We have another rpmsg driver(rpmsg-tty) for binary data transfer.

> OTOH, if it text data, why do you need to take all strings at once?

Remote side may decide to buffer more log to reduce the IPC number
since IPC is a time consuming operation.

>  It might be worse from performance prospective (if you know how and when printk() supplies buffer to the console).

Yes, it's very slow if the log send to serial console. But in
production environment, printk normally just save in ram and viewed by
dmesg which is very fast.

>
> > +     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()?

I use memcpy initially, but found that the unaligned exception happen randomly.
To avoid the cache issue, the IPC memory normally map as device memory, but
ARM just allow the alignment access to this type of memory.

>
> > +             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?

Yes, the callback come from a dedicated work thread.

>
> > +}
>
> > +#ifdef CONFIG_PM_SLEEP
>
> You can consider to use __maybe_unused annotation to the below function.

Ok.

>
> > +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.

Ok.

>
> > +};
>
> --
> With Best Regards,
> Andy Shevchenko
>
>

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

[Andy Shevchenko]

On Fri, Feb 15, 2019 at 12:31:17AM +0800, xiang xiao wrote:
> On Thu, Feb 14, 2019 at 9:09 PM Andy Shevchenko
> <andriy.shevchenko@linux.intel.com> wrote:
> > On Thu, Feb 14, 2019 at 02:02:38PM +0800, Xiang Xiao wrote:

> > > 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?
> >
> 
> But, I want to make it more explicitly and prepare for struct expansion later.

How? Why it's not in this patch / patch series?

> > > +     /* 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?
> 
> This driver is just for log/printf redirection, so we could safely
> assume the data is pure text.

Then I don't see a point to use memrchr() at all here.

Use strchr or strrchr().

> > OTOH, if it text data, why do you need to take all strings at once?
> 
> Remote side may decide to buffer more log to reduce the IPC number
> since IPC is a time consuming operation.

So, you always can do something like

p = msg->data;
while (...strsep(..., "\n")) {
	pr_info("%s\n", token);
	...
}

> 
> >  It might be worse from performance prospective (if you know how and when printk() supplies buffer to the console).
> 
> Yes, it's very slow if the log send to serial console. But in
> production environment, printk normally just save in ram and viewed by
> dmesg which is very fast.

You may not do such assumptions. For someone it would be RAM, for some
customers it might be a slow channel.


> > > +             strncpy(priv->buf + priv->next, msg->data + printed, copied);
> >
> > Hmm... shouldn't be memcpy()?
> 
> I use memcpy initially, but found that the unaligned exception happen randomly.
> To avoid the cache issue, the IPC memory normally map as device memory, but
> ARM just allow the alignment access to this type of memory.

So, than it's an architecture level issue. With strncpy() here you will get a
pretty rightful GCC warning.

> > > +     /* 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?
> 
> Yes, the callback come from a dedicated work thread.

Please, add a comment explaining that.

-- 
With Best Regards,
Andy Shevchenko

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

[xiang xiao]

On Fri, Feb 15, 2019 at 11:06 PM Andy Shevchenko
<andriy.shevchenko@linux.intel.com> wrote:
>
> On Fri, Feb 15, 2019 at 12:31:17AM +0800, xiang xiao wrote:
> > On Thu, Feb 14, 2019 at 9:09 PM Andy Shevchenko
> > <andriy.shevchenko@linux.intel.com> wrote:
> > > On Thu, Feb 14, 2019 at 02:02:38PM +0800, Xiang Xiao wrote:
>
> > > > 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?
> > >
> >
> > But, I want to make it more explicitly and prepare for struct expansion later.
>
> How? Why it's not in this patch / patch series?

Just for future, not now:).
Since this structure is shared by the different CPU/OS, it's better to
indicate the packed explicitly.

>
> > > > +     /* 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?
> >
> > This driver is just for log/printf redirection, so we could safely
> > assume the data is pure text.
>
> Then I don't see a point to use memrchr() at all here.
>
> Use strchr or strrchr().

Yes, use strnchr is enough, I will remove memrchr in the next review.

>
> > > OTOH, if it text data, why do you need to take all strings at once?
> >
> > Remote side may decide to buffer more log to reduce the IPC number
> > since IPC is a time consuming operation.
>
> So, you always can do something like
>
> p = msg->data;
> while (...strsep(..., "\n")) {
>         pr_info("%s\n", token);
>         ...
> }

Can't use strsep here, since log come from remote isn't terminated by '\0'.

>
> >
> > >  It might be worse from performance prospective (if you know how and when printk() supplies buffer to the console).
> >
> > Yes, it's very slow if the log send to serial console. But in
> > production environment, printk normally just save in ram and viewed by
> > dmesg which is very fast.
>
> You may not do such assumptions. For someone it would be RAM, for some
> customers it might be a slow channel.

But we need reduce the IPC number, so both fast/slow channel could get
the benefit.

>
>
> > > > +             strncpy(priv->buf + priv->next, msg->data + printed, copied);
> > >
> > > Hmm... shouldn't be memcpy()?
> >
> > I use memcpy initially, but found that the unaligned exception happen randomly.
> > To avoid the cache issue, the IPC memory normally map as device memory, but
> > ARM just allow the alignment access to this type of memory.
>
> So, than it's an architecture level issue. With strncpy() here you will get a
> pretty rightful GCC warning.
>

Why GCC warning strncpy here?

> > > > +     /* 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?
> >
> > Yes, the callback come from a dedicated work thread.
>
> Please, add a comment explaining that.
>
Will add in the next review.

> --
> With Best Regards,
> Andy Shevchenko
>
>