add disksnoop example

Author: varun-r-mallya

BCC-Examples/disksnoop.py

@@ -0,0 +1,57 @@
+from vmlinux import struct_request, struct_pt_regs
+from pythonbpf import bpf, section, bpfglobal, compile_to_ir, compile, map
+from pythonbpf.helper import ktime
+from pythonbpf.maps import HashMap
+import logging
+from ctypes import c_int64, c_uint64, c_uint32, c_int32
+
+# Constants
+REQ_WRITE = 1  # from include/linux/blk_types.h
+
+@bpf
+@map
+def start() -> HashMap:
+    return HashMap(key=c_uint64, value=c_uint64, max_entries=10240)
+
+@bpf
+@section("kprobe/blk_mq_end_request")
+def trace_completion(ctx: struct_pt_regs) -> c_int64:
+    # Get request pointer from first argument
+    req_ptr = ctx.di
+    req = struct_request(ctx.di)
+    # Print: data_len, cmd_flags, latency_us
+    data_len = req.__data_len
+    cmd_flags = req.cmd_flags
+    # Lookup start timestamp
+    req_tsp = start.lookup(req_ptr)
+    if req_tsp:
+        # Calculate delta in nanoseconds
+        delta = ktime() - req_tsp
+
+        # Convert to microseconds for printing
+        delta_us = delta // 1000
+
+        print(f"{data_len} {cmd_flags:x} {delta_us}\n")
+
+        # Delete the entry
+        start.delete(req_ptr)
+
+    return c_int64(0)
+
+@bpf
+@section("kprobe/blk_mq_start_request")
+def trace_start(ctx1: struct_pt_regs) -> c_int32:
+    req = ctx1.di
+    ts = ktime()
+    start.update(req, ts)
+    return c_int32(0)
+
+@bpf
+@bpfglobal
+def LICENSE() -> str:
+    return "GPL"
+
+
+if __name__ == "__main__":
+    compile_to_ir("disksnoop.py", "disksnoop.ll", loglevel=logging.INFO)
+    compile()

tests/c-form/disksnoop.bpf.c

@@ -0,0 +1,66 @@
+// disksnoop.bpf.c
+// eBPF program (compile with: clang -O2 -g -target bpf -c disksnoop.bpf.c -o disksnoop.bpf.o)
+
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_core_read.h>
+
+char LICENSE[] SEC("license") = "GPL";
+
+struct {
+	__uint(type, BPF_MAP_TYPE_HASH);
+	__type(key, __u64);
+	__type(value, __u64);
+	__uint(max_entries, 10240);
+} start_map SEC(".maps");
+
+/* kprobe: record start timestamp keyed by request pointer */
+SEC("kprobe/blk_mq_start_request")
+int trace_start(struct pt_regs *ctx)
+{
+	/* request * is first arg */
+	__u64 reqp = (__u64)(ctx->di);
+	__u64 ts = bpf_ktime_get_ns();
+
+	bpf_map_update_elem(&start_map, &reqp, &ts, BPF_ANY);
+
+//	/* optional debug:
+	bpf_printk("start: req=%llu ts=%llu\n", reqp, ts);
+//	*/
+	return 0;
+}
+
+/* completion: compute latency and print data_len, cmd_flags, latency_us */
+SEC("kprobe/blk_mq_end_request")
+int trace_completion(struct pt_regs *ctx)
+{
+	__u64 reqp = (__u64)(ctx->di);
+	__u64 *tsp;
+	__u64 now_ns;
+	__u64 delta_ns;
+	__u64 delta_us = 0;
+    bpf_printk("%lld", reqp);
+	tsp = bpf_map_lookup_elem(&start_map, &reqp);
+	if (!tsp)
+		return 0;
+
+	now_ns = bpf_ktime_get_ns();
+	delta_ns = now_ns - *tsp;
+	delta_us = delta_ns / 1000;
+
+	/* read request fields using CO-RE; needs vmlinux.h/BTF */
+	__u32 data_len = 0;
+	__u32 cmd_flags = 0;
+
+	/* __data_len is usually a 32/64-bit; use CORE read to be safe */
+	data_len = ( __u32 ) BPF_CORE_READ((struct request *)reqp, __data_len);
+	cmd_flags = ( __u32 ) BPF_CORE_READ((struct request *)reqp, cmd_flags);
+
+	/* print: "<bytes> <flags_hex> <latency_us>" */
+	bpf_printk("%u %x %llu\n", data_len, cmd_flags, delta_us);
+
+	/* remove from map */
+	bpf_map_delete_elem(&start_map, &reqp);
+
+	return 0;
+}