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Date: Thu, 3 Sep 2009 16:25:57 -0400
From: Jason Baron <jbaron@...hat.com>
To: linux-kernel@...r.kernel.org
Cc: mathieu.desnoyers@...ymtl.ca, roland@...hat.com, rth@...hat.com,
mingo@...e.hu
Subject: [PATCH 2/4] RFC: jump label example usage
Example cases to see how jump patching can be used:
echo a '1' into <debugfs>/jump/enabled to see a 'doing tracing' printk
echo a '0' into <debugfs>/jump/enabled to see a 'not doing tracing' printk
The codepaths are updated using code patching.
Signed-off-by: Jason Baron <jbaron@...hat.com>
---
kernel/jump_label.c | 133 +++++++++++++++++++++++++++++++++++++++++++++++++++
1 files changed, 133 insertions(+), 0 deletions(-)
diff --git a/kernel/jump_label.c b/kernel/jump_label.c
index f6be1eb..0bc0b2d 100644
--- a/kernel/jump_label.c
+++ b/kernel/jump_label.c
@@ -120,10 +120,143 @@ int run_make_nop(char *name)
#endif
+static ssize_t read_enabled_file_jump(struct file *file,
+ char __user *user_buf, size_t count, loff_t *ppos)
+{
+ char buf[3];
+ ssize_t val;
+
+ if (jump_enabled)
+ buf[0] = '1';
+ else
+ buf[0] = '0';
+ buf[1] = '\n';
+ buf[2] = 0x00;
+
+ val = simple_read_from_buffer(user_buf, count, ppos, buf, 2);
+ JUMP_LABEL_IF(trace, trace_label, jump_enabled);
+ printk("not doing tracing\n");
+if (0) {
+trace_label:
+ printk("doing tracing: %d\n", file);
+}
+ printk("val is: %d\n", val);
+ return val;
+}
+
+static ssize_t read_enabled_file_jump2(struct file *file,
+ char __user *user_buf, size_t count, loff_t *ppos)
+{
+ char buf[3];
+ ssize_t val;
+
+ if (jump_enabled2)
+ buf[0] = '1';
+ else
+ buf[0] = '0';
+ buf[1] = '\n';
+ buf[2] = 0x00;
+
+ val = simple_read_from_buffer(user_buf, count, ppos, buf, 2);
+ JUMP_LABEL_IF(trace2, trace_label, jump_enabled2);
+ printk("not doing tracing 2\n");
+if (0) {
+trace_label:
+ printk("doing tracing 2: %d\n", file);
+}
+ printk("val is: %d\n", val);
+ return val;
+}
+
+static ssize_t write_enabled_file_jump(struct file *file,
+ const char __user *user_buf, size_t count, loff_t *ppos)
+{
+ char buf[32];
+ int buf_size;
+
+ buf_size = min(count, (sizeof(buf)-1));
+ if (copy_from_user(buf, user_buf, buf_size))
+ return -EFAULT;
+
+ switch (buf[0]) {
+ case 'y':
+ case 'Y':
+ case '1':
+ jump_enabled = 1;
+ run_make_jump("trace");
+ break;
+ case 'n':
+ case 'N':
+ case '0':
+ jump_enabled = 0;
+ run_make_nop("trace");
+ break;
+ }
+
+ return count;
+}
+
+static ssize_t write_enabled_file_jump2(struct file *file,
+ const char __user *user_buf, size_t count, loff_t *ppos)
+{
+ char buf[32];
+ int buf_size;
+
+ buf_size = min(count, (sizeof(buf)-1));
+ if (copy_from_user(buf, user_buf, buf_size))
+ return -EFAULT;
+
+ switch (buf[0]) {
+ case 'y':
+ case 'Y':
+ case '1':
+ jump_enabled2 = 1;
+ run_make_jump("trace2");
+ break;
+ case 'n':
+ case 'N':
+ case '0':
+ jump_enabled2 = 0;
+ run_make_nop("trace2");
+ break;
+ }
+
+ return count;
+}
+
+static struct file_operations fops_jump = {
+ .read = read_enabled_file_jump,
+ .write = write_enabled_file_jump,
+};
+
+static struct file_operations fops_jump2 = {
+ .read = read_enabled_file_jump2,
+ .write = write_enabled_file_jump2,
+};
+
static int __jump_label_init(void)
{
+ struct dentry *dir, *file;
+ unsigned int value = 1;
struct jump_entry *iter;
+ dir = debugfs_create_dir("jump", NULL);
+ if (!dir)
+ return -ENOMEM;
+
+ file = debugfs_create_file("enabled", 0600, dir,
+ &value, &fops_jump);
+ if (!file) {
+ debugfs_remove(dir);
+ return -ENOMEM;
+ }
+
+ file = debugfs_create_file("enabled2", 0600, dir,
+ &value, &fops_jump2);
+ if (!file) {
+ debugfs_remove(dir);
+ return -ENOMEM;
+ }
#ifdef HAVE_STATIC_JUMP
printk("__start___jump_table is: %p\n", __start___jump_table);
--
1.6.2.5
--
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