man: document tracepoint provider

man/ply.1.ronn

@@ -127,8 +127,9 @@ Data can be stored in a map by assigning a value to a given key:
 
     mapname[exprs] = expr
 
-If a map key is assigned the special value _nil_, the key is deleted
-and will return its zero value if referenced again.
+The _delete_ keyword can be used to remove an association from a map:
+
+    delete mapname[exprs]
 
 
 ### Aggregations
@@ -262,6 +263,68 @@ _kretprobe_ specific function:
     Return value of the probed function.
 
 
+### tracepoint
+
+The tracepoint provider can instrument all stable tracepoints in the
+kernel. They are identified by their relative path from the
+`/sys/kernel/debug/tracing/events` directory, where each leaf
+directory corresponds to a tracepoint.
+
+Examples:
+
+  * _tracepoint:sched/sched_wakeup_: Trace every time a process is
+    awoken.
+  * _tracepoint:irq/irq_handler_entry_: Trace every time an interrupt
+    is handled.
+
+Variables:
+
+  * `struct <X> *data`:
+
+    A struct is dynamically generated for each tracepoint by parsing
+    its `format` file. I.e. if the contents of the format file looks
+    like the following:
+
+    ```
+name: tcp_send_reset
+ID: 1304
+format:
+	field:unsigned short common_type;	offset:0;	size:2;	signed:0;
+	field:unsigned char common_flags;	offset:2;	size:1;	signed:0;
+	field:unsigned char common_preempt_count;	offset:3;	size:1;	signed:0;
+	field:int common_pid;	offset:4;	size:4;	signed:1;
+
+	field:const void * skbaddr;	offset:8;	size:8;	signed:0;
+	field:const void * skaddr;	offset:16;	size:8;	signed:0;
+	field:__u16 sport;	offset:24;	size:2;	signed:0;
+	field:__u16 dport;	offset:26;	size:2;	signed:0;
+	field:__u8 saddr[4];	offset:28;	size:4;	signed:0;
+	field:__u8 daddr[4];	offset:32;	size:4;	signed:0;
+	field:__u8 saddr_v6[16];	offset:36;	size:16;	signed:0;
+	field:__u8 daddr_v6[16];	offset:52;	size:16;	signed:0;
+
+    ```
+
+    Then `data` would point to a struct of the following type:
+
+    ```
+struct data {
+    unsigned short common_type;
+    unsigned char common_flags;
+    unsigned char common_preempt_count;
+    int common_pid;
+
+    const void * skbaddr;
+    const void * skaddr;
+    __u16 sport;
+    __u16 dport;
+    __u8 saddr[4];
+    __u8 daddr[4];
+    __u8 saddr_v6[16];
+    __u8 daddr_v6[16];
+};
+    ```
+
 ## EXAMPLE
 
 ### Extracting data