merge disksnoop example

README.md

@@ -60,7 +60,7 @@ pair of .c and .py files, and some are directories of files.
 Examples:
 
 - examples/tracing/[bitehist.py](examples/tracing/bitehist.py): Block I/O size histogram. [Examples](examples/tracing/bitehist_example.txt).
-- examples/tracing/[disksnoop.py](examples/tracing/disksnoop.py) examples/tracing/[disksnoop.c](examples/tracing/disksnoop.c): Trace block device I/O latency. [Examples](examples/tracing/disksnoop_example.txt).
+- examples/tracing/[disksnoop.py](examples/tracing/disksnoop.py): Trace block device I/O latency. [Examples](examples/tracing/disksnoop_example.txt).
 - examples/[hello_world.py](examples/hello_world.py): Prints "Hello, World!" for new processes.
 - examples/tracing/[tcpv4connect.py](examples/tracing/tcpv4connect.py): Trace TCP IPv4 active connections. [Examples](examples/tracing/tcpv4connect_example.txt).
 - examples/tracing/[trace_fields.py](examples/tracing/trace_fields.py): Simple example of printing fields from traced events.

examples/tracing/disksnoop.py

@@ -1,7 +1,7 @@
 #!/usr/bin/python
 #
 # disksnoop.py Trace block device I/O: basic version of iosnoop.
-# For Linux, uses BCC, eBPF. See .c file.
+# For Linux, uses BCC, eBPF. Embedded C.
 #
 # Written as a basic example of tracing latency.
 #
@@ -16,7 +16,32 @@
 REQ_WRITE = 1 # from include/linux/blk_types.h
 
 # load BPF program
-b = BPF(src_file="disksnoop.c")
+b = BPF(text="""
+#include <uapi/linux/ptrace.h>
+#include <linux/blkdev.h>
+
+BPF_HASH(start, struct request *);
+
+void trace_start(struct pt_regs *ctx, struct request *req) {
+ // stash start timestamp by request ptr
+ u64 ts = bpf_ktime_get_ns();
+
+ start.update(&req, &ts);
+}
+
+void trace_completion(struct pt_regs *ctx, struct request *req) {
+ u64 *tsp, delta;
+
+ tsp = start.lookup(&req);
+ if (tsp != 0) {
+ delta = bpf_ktime_get_ns() - *tsp;
+ bpf_trace_printk("%d %x %d\\n", req->__data_len,
+ req->cmd_flags, delta / 1000);
+ start.delete(&req);
+ }
+}
+""")
+
 b.attach_kprobe(event="blk_start_request", fn_name="trace_start")
 b.attach_kprobe(event="blk_mq_start_request", fn_name="trace_start")
 b.attach_kprobe(event="blk_account_io_completion", fn_name="trace_completion")