Re: [PATCH 1/3] drivers-core: make structured logging play nice with dynamic-debug

[Joe Perches <joe@perches.com>]

On Mon, 2012-07-23 at 09:07 -0400, Jason Baron wrote:
> On Thu, Jul 19, 2012 at 01:46:20PM -0600, Jim Cromie wrote:
> > commit c4e00daaa96d3a0786f1f4fe6456281c60ef9a16 changed __dev_printk
> > in a way that broke dynamic-debug's ability to control the dynamic
> > prefix of dev_dbg(dev,..), but not dev_dbg(NULL,..) or pr_debug(..),
> > which is why it wasnt noticed sooner.
> > 
> > When dev==NULL, __dev_printk() just calls printk(), which just works.
> > But otherwise, it assumed that level was always a string like "<L>"
> > and just plucked out the 'L', ignoring the rest.  However,
> > dynamic_emit_prefix() adds "[tid] module:func:line:" to the string,
> > those additions all got lost.
> >

I think this is not a really good approach.

3 depths of %pV can consume quite a lot of stack
and avoiding this is useful.

I'd much rather improve/centralize the mechanism
in dynamic_debug.c so that the extra recursion
depth is avoided.

Something like this:

o Remove KERN_DEBUG from dynamic_emit_prefix
o Make a function of create_syslog_header to format
  the header for printk_emit.
o Call printk_emit in dynamic_dev_dbg and dynamic_netdev_dbg
o Call printk_emit in __dev_printk
o Remove now unused EXPORT_SYMBOL(__netdev_printk)
o Neatening

Thoughts?

---

 drivers/base/core.c    |   55 +++++++++++++++++++++++++----------------
 include/linux/device.h |    6 +++-
 lib/dynamic_debug.c    |   63 ++++++++++++++++++++++++++++++++++++++---------
 net/core/dev.c         |    5 ++-
 4 files changed, 91 insertions(+), 38 deletions(-)

diff --git a/drivers/base/core.c b/drivers/base/core.c
index 346be8b..94f3803 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -1844,25 +1844,19 @@ void device_shutdown(void)
  */
 
 #ifdef CONFIG_PRINTK
-int __dev_printk(const char *level, const struct device *dev,
-		 struct va_format *vaf)
+int create_syslog_header(const struct device *dev, char *hdr, size_t hdrlen)
 {
-	char dict[128];
-	size_t dictlen = 0;
 	const char *subsys;
-
-	if (!dev)
-		return printk("%s(NULL device *): %pV", level, vaf);
+	size_t pos = 0;
 
 	if (dev->class)
 		subsys = dev->class->name;
 	else if (dev->bus)
 		subsys = dev->bus->name;
 	else
-		goto skip;
+		return 0;
 
-	dictlen += snprintf(dict + dictlen, sizeof(dict) - dictlen,
-			    "SUBSYSTEM=%s", subsys);
+	pos += snprintf(hdr + pos, hdrlen - pos, "SUBSYSTEM=%s", subsys);
 
 	/*
 	 * Add device identifier DEVICE=:
@@ -1878,24 +1872,39 @@ int __dev_printk(const char *level, const struct device *dev,
 			c = 'b';
 		else
 			c = 'c';
-		dictlen++;
-		dictlen += snprintf(dict + dictlen, sizeof(dict) - dictlen,
-				   "DEVICE=%c%u:%u",
-				   c, MAJOR(dev->devt), MINOR(dev->devt));
+		pos++;
+		pos += snprintf(hdr + pos, hdrlen - pos,
+				"DEVICE=%c%u:%u",
+				c, MAJOR(dev->devt), MINOR(dev->devt));
 	} else if (strcmp(subsys, "net") == 0) {
 		struct net_device *net = to_net_dev(dev);
 
-		dictlen++;
-		dictlen += snprintf(dict + dictlen, sizeof(dict) - dictlen,
-				    "DEVICE=n%u", net->ifindex);
+		pos++;
+		pos += snprintf(hdr + pos, hdrlen - pos,
+				"DEVICE=n%u", net->ifindex);
 	} else {
-		dictlen++;
-		dictlen += snprintf(dict + dictlen, sizeof(dict) - dictlen,
-				    "DEVICE=+%s:%s", subsys, dev_name(dev));
+		pos++;
+		pos += snprintf(hdr + pos, hdrlen - pos,
+				"DEVICE=+%s:%s", subsys, dev_name(dev));
 	}
-skip:
+
+	return pos;
+}
+EXPORT_SYMBOL(create_syslog_header);
+
+int __dev_printk(const char *level, const struct device *dev,
+		 struct va_format *vaf)
+{
+	char hdr[128];
+	size_t hdrlen;
+
+	if (!dev)
+		return printk("%s(NULL device *): %pV", level, vaf);
+
+	hdrlen = create_syslog_header(dev, hdr, sizeof(hdr));
+
 	return printk_emit(0, level[1] - '0',
-			   dictlen ? dict : NULL, dictlen,
+			   hdrlen ? hdr : NULL, hdrlen,
 			   "%s %s: %pV",
 			   dev_driver_string(dev), dev_name(dev), vaf);
 }
@@ -1914,6 +1923,7 @@ int dev_printk(const char *level, const struct device *dev,
 	vaf.va = &args;
 
 	r = __dev_printk(level, dev, &vaf);
+
 	va_end(args);
 
 	return r;
@@ -1933,6 +1943,7 @@ int func(const struct device *dev, const char *fmt, ...)	\
 	vaf.va = &args;						\
 								\
 	r = __dev_printk(kern_level, dev, &vaf);		\
+								\
 	va_end(args);						\
 								\
 	return r;						\
diff --git a/include/linux/device.h b/include/linux/device.h
index 6de9415..74863f0 100644
--- a/include/linux/device.h
+++ b/include/linux/device.h
@@ -884,12 +884,14 @@ extern const char *dev_driver_string(const struct device *dev);
 
 #ifdef CONFIG_PRINTK
 
+extern int create_syslog_header(const struct device *dev,
+				char *hdr, size_t hdrlen);
+
 extern int __dev_printk(const char *level, const struct device *dev,
 			struct va_format *vaf);
 extern __printf(3, 4)
 int dev_printk(const char *level, const struct device *dev,
-	       const char *fmt, ...)
-	;
+	       const char *fmt, ...);
 extern __printf(2, 3)
 int dev_emerg(const struct device *dev, const char *fmt, ...);
 extern __printf(2, 3)
diff --git a/lib/dynamic_debug.c b/lib/dynamic_debug.c
index 7ca29a0..08442e7 100644
--- a/lib/dynamic_debug.c
+++ b/lib/dynamic_debug.c
@@ -521,25 +521,23 @@ static char *dynamic_emit_prefix(const struct _ddebug *desc, char *buf)
 	int pos_after_tid;
 	int pos = 0;
 
-	pos += snprintf(buf + pos, remaining(pos), "%s", KERN_DEBUG);
 	if (desc->flags & _DPRINTK_FLAGS_INCL_TID) {
 		if (in_interrupt())
-			pos += snprintf(buf + pos, remaining(pos), "%s ",
-						"<intr>");
+			pos += snprintf(buf + pos, remaining(pos), "<intr> ");
 		else
 			pos += snprintf(buf + pos, remaining(pos), "[%d] ",
-						task_pid_vnr(current));
+					task_pid_vnr(current));
 	}
 	pos_after_tid = pos;
 	if (desc->flags & _DPRINTK_FLAGS_INCL_MODNAME)
 		pos += snprintf(buf + pos, remaining(pos), "%s:",
-					desc->modname);
+				desc->modname);
 	if (desc->flags & _DPRINTK_FLAGS_INCL_FUNCNAME)
 		pos += snprintf(buf + pos, remaining(pos), "%s:",
-					desc->function);
+				desc->function);
 	if (desc->flags & _DPRINTK_FLAGS_INCL_LINENO)
 		pos += snprintf(buf + pos, remaining(pos), "%d:",
-					desc->lineno);
+				desc->lineno);
 	if (pos - pos_after_tid)
 		pos += snprintf(buf + pos, remaining(pos), " ");
 	if (pos >= PREFIX_SIZE)
@@ -559,9 +557,13 @@ int __dynamic_pr_debug(struct _ddebug *descriptor, const char *fmt, ...)
 	BUG_ON(!fmt);
 
 	va_start(args, fmt);
+
 	vaf.fmt = fmt;
 	vaf.va = &args;
-	res = printk("%s%pV", dynamic_emit_prefix(descriptor, buf), &vaf);
+
+	res = printk(KERN_DEBUG "%s%pV",
+		     dynamic_emit_prefix(descriptor, buf), &vaf);
+
 	va_end(args);
 
 	return res;
@@ -580,9 +582,25 @@ int __dynamic_dev_dbg(struct _ddebug *descriptor,
 	BUG_ON(!fmt);
 
 	va_start(args, fmt);
+
 	vaf.fmt = fmt;
 	vaf.va = &args;
-	res = __dev_printk(dynamic_emit_prefix(descriptor, buf), dev, &vaf);
+
+	if (!dev) {
+		res = printk(KERN_DEBUG "(NULL device *): %pV", &vaf);
+	} else {
+		char dict[128];
+		size_t dictlen;
+
+		dictlen = create_syslog_header(dev, dict, sizeof(dict));
+
+		res = printk_emit(0, 7,
+				  dictlen ? dict : NULL, dictlen,
+				  "%s%s %s: %pV",
+				  dynamic_emit_prefix(descriptor, buf),
+				  dev_driver_string(dev), dev_name(dev), &vaf);
+	}
+
 	va_end(args);
 
 	return res;
@@ -592,20 +610,41 @@ EXPORT_SYMBOL(__dynamic_dev_dbg);
 #ifdef CONFIG_NET
 
 int __dynamic_netdev_dbg(struct _ddebug *descriptor,
-		      const struct net_device *dev, const char *fmt, ...)
+			 const struct net_device *dev, const char *fmt, ...)
 {
 	struct va_format vaf;
 	va_list args;
 	int res;
-	char buf[PREFIX_SIZE];
 
 	BUG_ON(!descriptor);
 	BUG_ON(!fmt);
 
 	va_start(args, fmt);
+
 	vaf.fmt = fmt;
 	vaf.va = &args;
-	res = __netdev_printk(dynamic_emit_prefix(descriptor, buf), dev, &vaf);
+
+	if (dev && dev->dev.parent) {
+		char buf[PREFIX_SIZE];
+		char dict[128];
+		size_t dictlen;
+
+		dictlen = create_syslog_header(dev->dev.parent,
+					       dict, sizeof(dict));
+
+		res = printk_emit(0, 7,
+				  dictlen ? dict : NULL, dictlen,
+				  "%s%s %s: %pV",
+				  dynamic_emit_prefix(descriptor, buf),
+				  dev_driver_string(dev->dev.parent),
+				  netdev_name(dev), &vaf);
+
+	} else if (dev) {
+		res = printk(KERN_DEBUG "%s: %pV", netdev_name(dev), &vaf);
+	} else {
+		res = printk(KERN_DEBUG "(NULL net_device): %pV", &vaf);
+	}
+
 	va_end(args);
 
 	return res;
diff --git a/net/core/dev.c b/net/core/dev.c
index 1cb0d8a..1651065 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -6324,7 +6324,7 @@ const char *netdev_drivername(const struct net_device *dev)
 	return empty;
 }
 
-int __netdev_printk(const char *level, const struct net_device *dev,
+static int __netdev_printk(const char *level, const struct net_device *dev,
 			   struct va_format *vaf)
 {
 	int r;
@@ -6339,7 +6339,6 @@ int __netdev_printk(const char *level, const struct net_device *dev,
 
 	return r;
 }
-EXPORT_SYMBOL(__netdev_printk);
 
 int netdev_printk(const char *level, const struct net_device *dev,
 		  const char *format, ...)
@@ -6354,6 +6353,7 @@ int netdev_printk(const char *level, const struct net_device *dev,
 	vaf.va = &args;
 
 	r = __netdev_printk(level, dev, &vaf);
+
 	va_end(args);
 
 	return r;
@@ -6373,6 +6373,7 @@ int func(const struct net_device *dev, const char *fmt, ...)	\
 	vaf.va = &args;						\
 								\
 	r = __netdev_printk(level, dev, &vaf);			\
+								\
 	va_end(args);						\
 								\
 	return r;						\