dynamic printk - core infrastructure

Add the ability to dynamically enable/disable pr_debug()/dev_dbg() in the kernel. Yes, these calls could be converted to printk(KERN_DEBUG), but there are enough to cause overhead. Additionally, the logs become difficult to read. Here, one can turn on and off these messages per .c source file via:

echo "add file.c" > /sys/kernel/debug/dynamic_printk/files echo "remove file.c" > /sys/kernel/debug/dynamic_printk/files

There is also a special 'all' value that turns on all the debugging messages.

Signed-off-by Jason Baron <[email protected]>

---

Add the ability to dynamically enable/disable pr_debug()/dev_dbg() in the kernel. Yes, these calls could be converted to printk(KERN_DEBUG), but there are enough to cause overhead. Additionally, the logs become difficult to read. Here, one can turn on and off these messages per .c source file via:

echo "add file.c" > /sys/kernel/debug/dynamic_printk/files echo "remove file.c" > /sys/kernel/debug/dynamic_printk/files

There is also a special 'all' value that turns on all the debugging messages.

Signed-off-by Jason Baron <[email protected]>

---

 include/linux/device.h |   12 ++
 include/linux/kernel.h |   11 ++
 lib/Kconfig.debug      |   34 ++++++
 lib/Makefile           |    2 
 lib/dynamic_printk.c   |  253 ++++++++++++++++++++++++++++++++++++++++++++++++
 5 files changed, 312 insertions(+), 0 deletions(-)
 create mode 100644 lib/dynamic_printk.c

include/linux/device.h +12 -0

index db375be..b007f61 100644
@@ -587,6 +587,17 @@ extern const char *dev_driver_string(struct device *dev);
 #define dev_info(dev, format, arg...)		\
 	dev_printk(KERN_INFO , dev , format , ## arg)
 
+#ifdef CONFIG_DYNAMIC_PRINTK
+extern void dyanmic_printk(char *, char *, ...);
+DECLARE_IMV(char, dynamic_debug_on);
+#define dev_dbg(dev, format, arg...)					\
+	do {								\
+	   if (unlikely(imv_read(dynamic_debug_on)))			\
+		dynamic_printk(__FILE__, KERN_DEBUG "%s %s: " format,	\
+				dev_driver_string(dev), (dev)->bus_id,	\
+				## arg);				\
+	} while (0)
+#else
 #ifdef DEBUG
 #define dev_dbg(dev, format, arg...)		\
 	dev_printk(KERN_DEBUG , dev , format , ## arg)

@@ -597,6 +608,7 @@ dev_dbg(struct device *dev, const char *fmt, ...)
 	return 0;
 }
 #endif
+#endif
 
 #ifdef VERBOSE_DEBUG
 #define dev_vdbg	dev_dbg

include/linux/kernel.h +1 -0

index ff356b2..a311e87 100644
@@ -14,6 +14,7 @@
 #include <linux/compiler.h>
 #include <linux/bitops.h>
 #include <linux/log2.h>
+#include <linux/immediate.h>
 #include <asm/byteorder.h>
 #include <asm/bug.h>
 

@@ -276,6 +277,15 @@ extern void print_hex_dump_bytes(const char *prefix_str, int prefix_type,
 #define pr_info(fmt, arg...) \

include/linux/kernel.h +2 -0

+#else
 #ifdef DEBUG
 /* If you are writing a driver, please use dev_dbg instead */
 #define pr_debug(fmt, arg...) \

@@ -286,6 +296,7 @@ static inline int __attribute__ ((format (printf, 1, 2))) pr_debug(const char *
 	return 0;
 }
 #endif
+#endif
 
 /*
  *      Display an IP address in readable format.

lib/Kconfig.debug +0 -0

index 0d8a5a4..5454c0a 100644

lib/Kconfig.debug +0 -0

 source "samples/Kconfig"

lib/dynamic_printk.c new file +136 -0

new file mode 100644
index 0000000..008496b
@@ -0,0 +1,253 @@
+/*
+ * lib/dynamic_printk.c
+ *
+ * make pr_debug()/dev_dbg() calls runtime configurable based upon their .c file
+ *
+ * Copyright (C) 2008 Red Hat, Inc., Jason Baron <[email protected]>
+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/uaccess.h>
+#include <linux/seq_file.h>
+#include <linux/debugfs.h>
+#include <linux/fs.h>
+#include <linux/proc_fs.h>
+#include <linux/spinlock.h>
+#include <linux/hash.h>
+
+#define FILE_HASH_BITS 5
+#define FILE_TABLE_SIZE (1 << FILE_HASH_BITS)
+
+DEFINE_IMV(char, dynamic_debug_on) = 0;
+EXPORT_IMV_SYMBOL_GPL(dynamic_debug_on);
+
+static int all;
+static struct hlist_head file_table[FILE_TABLE_SIZE] =
+	{ [0 ... FILE_TABLE_SIZE-1] = HLIST_HEAD_INIT };
+static DECLARE_MUTEX(debug_list_mutex);
+static int nr_entries;
+
+struct debug_name {
+	struct hlist_node hlist;
+	char *name;
+};
+
+static inline unsigned int name_hash(char *name)
+{
+	unsigned int hash = full_name_hash(name, strlen(name));
+	return (hash & ((1 << FILE_HASH_BITS) - 1));
+}
+
+static struct debug_name *find_debug_file(char *file_name)
+{
+	int found = 0;
+	struct hlist_head *head;
+	struct hlist_node *node;
+	struct debug_name *element;
+
+	head = &file_table[name_hash(file_name)];
+	rcu_read_lock();
+	hlist_for_each_entry_rcu(element, node, head, hlist) {
+		if (!strcmp(element->name, file_name)) {
+			found = 1;
+			break;
+		}
+	}
+	rcu_read_unlock();
+	if (found)
+		return element;
+	return NULL;
+}
+
+static int add_debug_file(char *file_name)
+{
+	struct debug_name *new;
+
+	if (find_debug_file(file_name))
+		return -EINVAL;
+	new = kmalloc(sizeof(struct debug_name), GFP_KERNEL);
+	if (!new)
+		return -ENOMEM;
+	INIT_HLIST_NODE(&new->hlist);
+	new->name = file_name;
+	hlist_add_head_rcu(&new->hlist,
+			&file_table[name_hash(new->name)]);
+	nr_entries++;
+	return 0;
+}
+
+static int remove_debug_file(char *file_name)
+{
+	struct debug_name *element;
+
+	element = find_debug_file(file_name);
+	if (element == NULL)
+		return -EINVAL;
+	hlist_del_rcu(&element->hlist);
+	synchronize_rcu();
+	kfree(element->name);
+	kfree(element);
+	nr_entries--;
+	return 0;
+}
+
+void dynamic_printk(char *filename, char *fmt, ...)
+{
+	va_list args;
+
+	va_start(args, fmt);
+	if (all)
+		vprintk(fmt, args);
+	else {
+		if (find_debug_file(filename))
+			vprintk(fmt, args);
+	}
+	va_end(args);
+}
+EXPORT_SYMBOL_GPL(dynamic_printk);
+
+static ssize_t pr_debug_write(struct file *file, const char __user *buf,
+				size_t length, loff_t *ppos)
+{
+	char *buffer, *file_name, *s;
+	int err;
+
+	if (!buf || length > PAGE_SIZE || length < 0)
+		return -EINVAL;
+
+	buffer = (char *)__get_free_page(GFP_KERNEL);
+	if (!buffer)
+		return -ENOMEM;
+
+	err = -EFAULT;
+	if (copy_from_user(buffer, buf, length))
+		goto out;
+
+	err = -EINVAL;
+	if (length < PAGE_SIZE)
+		buffer[length] = '\0';
+	else if (buffer[PAGE_SIZE-1])
+		goto out;
+
+	err = -EINVAL;
+	down(&debug_list_mutex);
+	if (!strncmp("add all", buffer, 7)) {
+		if (!all && (nr_entries == 0))

lib/dynamic_printk.c new file +82 -0

+		err = remove_debug_file(s);
+		if (!err && (nr_entries == 0) && !all)
+			imv_set(dynamic_debug_on, 0);
+	}
+	if (!err)
+		err = length;
+out_up:
+	up(&debug_list_mutex);
+out:
+	free_page((unsigned long)buffer);
+	return err;
+}
+
+static void *pr_debug_seq_start(struct seq_file *f, loff_t *pos)
+{
+	return (*pos < FILE_TABLE_SIZE) ? pos : NULL;
+}
+
+static void *pr_debug_seq_next(struct seq_file *s, void *v, loff_t *pos)
+{
+	(*pos)++;
+	if (*pos >= FILE_TABLE_SIZE)
+		return NULL;
+	return pos;
+}
+
+static void pr_debug_seq_stop(struct seq_file *s, void *v)
+{
+	/* Nothing to do */
+}
+
+static int pr_debug_seq_show(struct seq_file *s, void *v)
+{
+	struct hlist_head *head;
+	struct hlist_node *node;
+	struct debug_name *element;
+	unsigned int i = *(loff_t *) v;
+
+	if (i == 0 && all)
+		seq_printf(s, "all\n");
+	rcu_read_lock();
+	head = &file_table[i];
+	hlist_for_each_entry_rcu(element, node, head, hlist)
+		seq_printf(s, "%s\n", element->name);
+	rcu_read_unlock();
+	return 0;
+}
+
+static struct seq_operations pr_debug_seq_ops = {
+	.start = pr_debug_seq_start,
+	.next  = pr_debug_seq_next,
+	.stop  = pr_debug_seq_stop,
+	.show  = pr_debug_seq_show
+};
+
+static int pr_debug_open(struct inode *inode, struct file *filp)
+{
+	return seq_open(filp, &pr_debug_seq_ops);
+}
+
+static const struct file_operations pr_debug_operations = {
+	.open           = pr_debug_open,
+	.read           = seq_read,
+	.write          = pr_debug_write,
+	.llseek         = seq_lseek,
+	.release        = seq_release,
+};
+
+int __init dynamic_printk_init(void)
+{
+	struct dentry *dir, *file;
+
+	dir = debugfs_create_dir("dynamic_printk", NULL);
+	if (!dir)
+		return -ENOMEM;
+	file = debugfs_create_file("files", 0644, dir, NULL,
+					&pr_debug_operations);
+	if (!file) {
+		debugfs_remove(dir);
+		return -ENOMEM;
+	}
+	return 0;

Quoted 2 lines

echo "add file.c" > /sys/kernel/debug/dynamic_printk/files echo "remove file.c" > /sys/kernel/debug/dynamic_printk/files

Quoted 2 lines · Randy Dunlap

Quoted 2 lines

echo "add file.c" > /sys/kernel/debug/dynamic_printk/files echo "remove file.c" > /sys/kernel/debug/dynamic_printk/files

I think this would be better by module rather than filename. KBUILD_MODNAME would be a better choice.

Quoted 5 lines · Joe Perches

Quoted 2 lines · Randy Dunlap

Quoted 2 lines

echo "add file.c" > /sys/kernel/debug/dynamic_printk/files echo "remove file.c" > /sys/kernel/debug/dynamic_printk/files

I think this would be better by module rather than filename. KBUILD_MODNAME would be a better choice.

agreed. i think 'KBUILD_MODNAME" provides a better interface. The original implementation was using complete source pathnames, so they were unique. Are 'KBUILD_MODNAME's unique?