[PATCH v5 3.1.0-rc4-tip 2/26] Uprobes: Allow multiple consumers for an uprobe.

[Srikar Dronamraju <srikar@linux.vnet.ibm.com>]

Since there is a unique uprobe for a inode, offset combination, provide
an ability for users to have more than one consumer for a uprobe.

Each consumer will define a handler and a filter.  Handler specifies the
routine to run on hitting a probepoint.  Filter allows to selectively run
the handler on hitting the probepoint.  Handler/Filter will be relevant when
we handle probehit.

Signed-off-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
---
 include/linux/uprobes.h |   13 +++++++++++++
 kernel/uprobes.c        |   41 +++++++++++++++++++++++++++++++++++++++++
 2 files changed, 54 insertions(+), 0 deletions(-)

diff --git a/include/linux/uprobes.h b/include/linux/uprobes.h
index bfb85c4..bf31f7c 100644
--- a/include/linux/uprobes.h
+++ b/include/linux/uprobes.h
@@ -25,9 +25,22 @@
 
 #include <linux/rbtree.h>
 
+struct uprobe_consumer {
+	int (*handler)(struct uprobe_consumer *self, struct pt_regs *regs);
+	/*
+	 * filter is optional; If a filter exists, handler is run
+	 * if and only if filter returns true.
+	 */
+	bool (*filter)(struct uprobe_consumer *self, struct task_struct *task);
+
+	struct uprobe_consumer *next;
+};
+
 struct uprobe {
 	struct rb_node		rb_node;	/* node in the rb tree */
 	atomic_t		ref;
+	struct rw_semaphore	consumer_rwsem;
+	struct uprobe_consumer	*consumers;
 	struct inode		*inode;		/* Also hold a ref to inode */
 	loff_t			offset;
 };
diff --git a/kernel/uprobes.c b/kernel/uprobes.c
index e452147..ba9fd55 100644
--- a/kernel/uprobes.c
+++ b/kernel/uprobes.c
@@ -149,6 +149,7 @@ static struct uprobe *alloc_uprobe(struct inode *inode, loff_t offset)
 
 	uprobe->inode = igrab(inode);
 	uprobe->offset = offset;
+	init_rwsem(&uprobe->consumer_rwsem);
 
 	/* add to uprobes_tree, sorted on inode:offset */
 	cur_uprobe = insert_uprobe(uprobe);
@@ -162,6 +163,46 @@ static struct uprobe *alloc_uprobe(struct inode *inode, loff_t offset)
 	return uprobe;
 }
 
+/* Returns the previous consumer */
+static struct uprobe_consumer *add_consumer(struct uprobe *uprobe,
+				struct uprobe_consumer *consumer)
+{
+	down_write(&uprobe->consumer_rwsem);
+	consumer->next = uprobe->consumers;
+	uprobe->consumers = consumer;
+	up_write(&uprobe->consumer_rwsem);
+	return consumer->next;
+}
+
+/*
+ * For uprobe @uprobe, delete the consumer @consumer.
+ * Return true if the @consumer is deleted successfully
+ * or return false.
+ */
+static bool del_consumer(struct uprobe *uprobe,
+				struct uprobe_consumer *consumer)
+{
+	struct uprobe_consumer *con;
+	bool ret = false;
+
+	down_write(&uprobe->consumer_rwsem);
+	con = uprobe->consumers;
+	if (consumer == con) {
+		uprobe->consumers = con->next;
+		ret = true;
+	} else {
+		for (; con; con = con->next) {
+			if (con->next == consumer) {
+				con->next = consumer->next;
+				ret = true;
+				break;
+			}
+		}
+	}
+	up_write(&uprobe->consumer_rwsem);
+	return ret;
+}
+
 static void delete_uprobe(struct uprobe *uprobe)
 {
 	unsigned long flags;

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