Re: [2/3] Userspace probes prototype-take2

[Prasanna S Panchamukhi <prasanna@in.ibm.com>]

This patch provides the feature to insert the probes on the pages
that are not present in the memory during registeration.

To add readpage and readpages() hooks, two new elements
are added to uprobe_module object.
struct address_space_operations *ori_a_ops;
struct address_space_operations user_a_ops;

User space probe also allows the probes to be inserted within the
pages even that are not present in the memory at the time of
registration. This is done by adding hooks to readpage and readpages
routines. During registration, the address space operation object is
modified by replacing with userspace probes's specific readpage and
readpages routines. So that when the pages are readinto the memory
through the readpage and readpages address space operations, the
probes can be automatically inserted into those pages. These user
space readpage and readpages routines internally call the original
readpage() and readpages() routines and then check if the probes are
to be added to these pages and then insert the probes on these pages.
Overhead of adding these hooks are limited to the application on
which probes are inserted.

While unregiteration, care should be taken to replace the readpage and
readpages() hooks by original routines if no probes exists on that
application.

Signed-of-by: Prasanna S Panchamukhi <prasanna@in.ibm.com>

 include/linux/namei.h |    1 

diff -puN kernel/kprobes.c~kprobes_userspace_probes_hook_readpage kernel/kprobes.c

diff -puN kernel/kprobes.c~kprobes_userspace_probes_hook_readpage kernel/kprobes.c


 kernel/kprobes.c |  116 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 files changed, 116 insertions(+)

diff -puN kernel/kprobes.c~kprobes_userspace_probes_hook_readpage kernel/kprobes.c
--- linux-2.6.16-rc1-mm5/kernel/kprobes.c~kprobes_userspace_probes_hook_readpage	2006-02-08 19:21:09.000000000 +0530
+++ linux-2.6.16-rc1-mm5-prasanna/kernel/kprobes.c	2006-02-08 19:21:09.000000000 +0530
@@ -769,6 +769,110 @@ static struct uprobe_module __kprobes *g
 	return NULL;
 }
 
+static inline void insert_readpage_uprobe(struct page *page,
+	struct address_space *mapping, struct uprobe *uprobe)
+{
+	if (find_page_probe(uprobe->offset >> PAGE_CACHE_SHIFT,
+				page->index << PAGE_CACHE_SHIFT)) {
+		map_uprobe_page(page, uprobe, insert_kprobe_user);
+		flush_vma(mapping, page, uprobe);
+	}
+}
+
+/**
+ *  This function hooks the readpages() of all modules that have active probes
+ *  on them. The original readpages() is called for the given
+ *  inode/address_space to actually read the pages into the memory. Then all
+ *  probes that are specified on these pages are inserted.
+ */
+static int __kprobes uprobe_readpages(struct file *file,
+				struct address_space *mapping,
+				struct list_head *pages, unsigned nr_pages)
+{
+	int retval = 0;
+	struct page *page;
+	struct uprobe_module *umodule;
+	struct uprobe *uprobe = NULL;
+	struct hlist_node *node;
+
+	mutex_lock(&uprobe_mutex);
+
+	umodule = get_module_by_inode(file->f_dentry->d_inode);
+	if (!umodule) {
+		printk("uprobe_readpages: we don't have a module \
+				associated with this file.. Aborting\n");
+		retval = -EINVAL;
+		goto out;
+	}
+
+	/* call original readpages() */
+	retval = umodule->ori_a_ops->readpages(file, mapping, pages, nr_pages);
+	if (retval < 0)
+		goto out;
+
+	/*
+	 * TODO: Walk through readpages page list and get
+	 * pages with probes instead of find_get_page().
+	 */
+	mutex_lock(&kprobe_mutex);
+	hlist_for_each_entry(uprobe, node, &umodule->ulist_head, ulist) {
+		page = find_get_page(mapping,
+				uprobe->offset >> PAGE_CACHE_SHIFT);
+		if (!page)
+			continue;
+
+		if (!uprobe->kp.opcode)
+			insert_readpage_uprobe(page, mapping, uprobe);
+		page_cache_release(page);
+	}
+	mutex_unlock(&kprobe_mutex);
+
+out:
+	mutex_unlock(&uprobe_mutex);
+	return retval;
+}
+
+/**
+ *  This function hooks the readpage() of all modules that have active probes
+ *  on them. The original readpage() is called for the given inode/address_space
+ *  to actually read the pages into the memory. Then all probes that are
+ *  specified on this page are inserted.
+ */
+int __kprobes uprobe_readpage(struct file *file, struct page *page)
+{
+	int retval = 0;
+	struct uprobe_module *umodule;
+	struct uprobe *uprobe = NULL;
+	struct hlist_node *node;
+	struct address_space *mapping = file->f_dentry->d_inode->i_mapping;
+
+	mutex_lock(&uprobe_mutex);
+	umodule = get_module_by_inode(file->f_dentry->d_inode);
+	if (!umodule) {
+		printk("uprobe_readpages: we don't have a module \
+				associated with this file.. Aborting\n");
+		retval = -EINVAL;
+		goto out;
+	}
+
+	/* call original readpage() */
+	retval = umodule->ori_a_ops->readpage(file, page);
+	if (retval < 0)
+		goto out;
+
+	mutex_lock(&kprobe_mutex);
+	hlist_for_each_entry(uprobe, node, &umodule->ulist_head, ulist) {
+		if (!uprobe->kp.opcode)
+			insert_readpage_uprobe(page, mapping, uprobe);
+	}
+	mutex_unlock(&kprobe_mutex);
+
+out:
+	mutex_unlock(&uprobe_mutex);
+
+	return retval;
+}
+
 /**
  * Gets exclusive write access to the given inode to ensure that the file
  * on which probes are currently applied does not change. Use the function,
@@ -799,9 +903,17 @@ static inline int ex_write_unlock(struct
 static void __kprobes get_inode_ops(struct uprobe *uprobe,
 				   struct uprobe_module *umodule)
 {
+	struct address_space *as;
+
 	INIT_HLIST_HEAD(&umodule->ulist_head);
 	hlist_add_head(&uprobe->ulist, &umodule->ulist_head);
 	list_add(&umodule->mlist, &uprobe_module_list);
+	as = umodule->nd.dentry->d_inode->i_mapping;
+	umodule->ori_a_ops = as->a_ops;
+	umodule->user_a_ops = *as->a_ops;
+	umodule->user_a_ops.readpage = uprobe_readpage;
+	umodule->user_a_ops.readpages = uprobe_readpages;
+	as->a_ops = &umodule->user_a_ops;
 }
 
 int __kprobes remove_kprobe_user(struct uprobe *uprobe, unsigned long *address,
@@ -811,6 +923,7 @@ int __kprobes remove_kprobe_user(struct 
 	int cleanup_p;
 
 	p = &uprobe->kp;
+	 /*TODO: change it to spin lock, we enter here holding i_mmap_lock */
 	mutex_lock(&kprobe_mutex);
 	old_p = get_kprobe_user(uprobe->inode, uprobe->offset);
 	if (unlikely(!old_p)) {
@@ -887,6 +1000,9 @@ void __kprobes unregister_uprobe(struct 
 	hlist_del(&uprobe->ulist);
 	if (hlist_empty(&umodule->ulist_head)) {
 		list_del(&umodule->mlist);
+		umodule->nd.dentry->d_inode->i_mapping->a_ops =
+							umodule->ori_a_ops;
+
 		ex_write_unlock(uprobe->inode);
 		path_release(&umodule->nd);
 		kfree(umodule);

_
-- 
Prasanna S Panchamukhi
Linux Technology Center
India Software Labs, IBM Bangalore
Email: prasanna@in.ibm.com
Ph: 91-80-51776329