// Copyright (c) 2015 Brendan Gregg.
// Licensed under the Apache License, Version 2.0 (the "License")

#include <uapi/linux/ptrace.h>
#include <linux/blkdev.h>

BPF_HASH(start, struct request *);
BPF_HISTOGRAM(dist);

// time block I/O
int trace_req_start(struct pt_regs *ctx, struct request *req)
{
    u64 ts = bpf_ktime_get_ns();
    start.update(&req, &ts);
    return 0;
}

// output
int trace_req_done(struct pt_regs *ctx, struct request *req)
{
    u64 *tsp, delta;

    // fetch timestamp and calculate delta
    tsp = start.lookup(&req);
    if (tsp == 0) {
        return 0;   // missed issue
    }
    delta = bpf_ktime_get_ns() - *tsp;
    delta /= 1000;  // usec

    // store as histogram
    dist.increment(bpf_log2l(delta));

    start.delete(&req);
    return 0;
}