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Subject[patch 1/3] 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 <jbaron@redhat.com>
---

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


diff --git a/include/linux/device.h b/include/linux/device.h
index db375be..b007f61 100644
--- a/include/linux/device.h
+++ b/include/linux/device.h
@@ -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
diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index ff356b2..a311e87 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -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...) \
printk(KERN_INFO fmt, ##arg)

+#ifdef CONFIG_DYNAMIC_PRINTK
+extern void dynamic_printk(char *, char *, ...);
+DECLARE_IMV(char, dynamic_debug_on);
+#define pr_debug(fmt, ...) \
+ do { \
+ if (unlikely(imv_read(dynamic_debug_on))) \
+ dynamic_printk(__FILE__, KERN_DEBUG fmt, ##__VA_ARGS__);\
+ } while (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.
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 0d8a5a4..5454c0a 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -615,4 +615,38 @@ config PROVIDE_OHCI1394_DMA_INIT

See Documentation/debugging-via-ohci1394.txt for more information.

+config DYNAMIC_PRINTK
+ bool "Enable dynamic printk() call support"
+ default y
+ depends on PRINTK
+ help
+
+ allows pr_debug() and dev_dbg() calls to be dynamically enabled based
+ upon their .c source file. Traditionally, these calls are only
+ enabled if one set #define DEBUG and recompiled the kernel. This
+ option obviates time consuming re-compiles.
+
+ The impact of this compile option is a larger kerenl text size ~1%.
+ However, if CONFIG_IMMEDIATE is set, the run-time impact is
+ negligible. Without CONFIG_IMMEDIATE set, a global variable is
+ referenced for each pr_debug() and dev_dbg() calls.
+
+ Usage:
+
+ The printing of pr_debug() and dev_dbg() is controlled by the
+ debugfs file, dynamic_printk/files.
+
+ echo "add foo.c" > dynamic_printk/files
+ echo "remove foo.c" > dynamic_printk/files
+
+ Also, a special "all" value will print all pr_debug() and dev_dbg()
+ calls. ie:
+
+ echo "add all" > dynamic_printk/files
+ echo "remove all" > dynamic_printk/files
+
+ Finally, passing "dynamic_printk" at the command line enables all
+ pr_debug() and dev_dbg() call to come out (same as "all"). This mode
+ can be disabled via a "remove all"
+
source "samples/Kconfig"
diff --git a/lib/Makefile b/lib/Makefile
index 543f250..5cb6ddb 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -67,6 +67,8 @@ obj-$(CONFIG_AUDIT_GENERIC) += audit.o
obj-$(CONFIG_SWIOTLB) += swiotlb.o
obj-$(CONFIG_FAULT_INJECTION) += fault-inject.o

+obj-$(CONFIG_DYNAMIC_PRINTK) += dynamic_printk.o
+
lib-$(CONFIG_GENERIC_BUG) += bug.o

hostprogs-y := gen_crc32table
diff --git a/lib/dynamic_printk.c b/lib/dynamic_printk.c
new file mode 100644
index 0000000..008496b
--- /dev/null
+++ b/lib/dynamic_printk.c
@@ -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 <jbaron@redhat.com>
+ */
+
+#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))
+ imv_set(dynamic_debug_on, 1);
+ all = 1;
+ err = 0;
+ } else if (!strncmp("remove all", buffer, 10)) {
+ if (all && (nr_entries == 0))
+ imv_set(dynamic_debug_on, 0);
+ all = 0;
+ err = 0;
+ } else if (!strncmp("add ", buffer, 4)) {
+ s = strstrip(buffer+4);
+ file_name = kmalloc(strlen(s)+1, GFP_KERNEL);
+ if (!file_name) {
+ err = -ENOMEM;
+ goto out_up;
+ }
+ file_name = strcpy(file_name, s);
+ err = add_debug_file(file_name);
+ if (err && err != -ENOMEM)
+ kfree(file_name);
+ if (!err && (nr_entries == 1) && !all)
+ imv_set(dynamic_debug_on, 1);
+ } else if (!strncmp("remove ", buffer, 7)) {
+ s = strstrip(buffer+7);
+ 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;
+}
+__initcall(dynamic_printk_init);
+
+static int __init dynamic_printk_setup(char *str)
+{
+ if (str)
+ return -ENOENT;
+ all = 1;
+ imv_set(dynamic_debug_on, 1);
+ return 0;
+}
+early_param("dynamic_printk", dynamic_printk_setup);

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