biosnoop.c

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

// This code is taken from: https://github.com/iovisor/bcc/blob/master/tools/biosnoop.py
//
// Copyright (c) 2015 Brendan Gregg.
// Licensed under the Apache License, Version 2.0 (the "License")

struct val_t {
    u64 ts;
    u32 pid;
    char name[TASK_COMM_LEN];
};

struct data_t {
    u32 pid;
    u64 rwflag;
    u64 delta;
    u64 qdelta;
    u64 sector;
    u64 len;
    u64 ts;
    char disk_name[DISK_NAME_LEN];
    char name[TASK_COMM_LEN];
};

BPF_HASH(start, struct request *);
BPF_HASH(infobyreq, struct request *, struct val_t);
BPF_PERF_OUTPUT(events);

// cache PID and comm by-req
int trace_pid_start(struct pt_regs *ctx, struct request *req)
{
    struct val_t val = {};
    u64 ts;

    if (bpf_get_current_comm(&val.name, sizeof(val.name)) == 0) {
        val.pid = bpf_get_current_pid_tgid() >> 32;
        if (##QUEUE##) {
            val.ts = bpf_ktime_get_ns();
        }
        infobyreq.update(&req, &val);
    }
    return 0;
}

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

// output
int trace_req_completion(struct pt_regs *ctx, struct request *req)
{
    u64 *tsp;
    struct val_t *valp;
    struct data_t data = {};
    u64 ts;

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

    valp = infobyreq.lookup(&req);
    if (valp == 0) {
        data.len = req->__data_len;
        strcpy(data.name, "?");
    } else {
        if (##QUEUE##) {
            data.qdelta = *tsp - valp->ts;
        }
        data.pid = valp->pid;
        data.len = req->__data_len;
        data.sector = req->__sector;
        bpf_probe_read(&data.name, sizeof(data.name), valp->name);
        struct gendisk *rq_disk = req->rq_disk;
        bpf_probe_read(&data.disk_name, sizeof(data.disk_name),
                       rq_disk->disk_name);
    }

/*
 * The following deals with a kernel version change (in mainline 4.7, although
 * it may be backported to earlier kernels) with how block request write flags
 * are tested. We handle both pre- and post-change versions here. Please avoid
 * kernel version tests like this as much as possible: they inflate the code,
 * test, and maintenance burden.
 */
#ifdef REQ_WRITE
    data.rwflag = !!(req->cmd_flags & REQ_WRITE);
#elif defined(REQ_OP_SHIFT)
    data.rwflag = !!((req->cmd_flags >> REQ_OP_SHIFT) == REQ_OP_WRITE);
#else
    data.rwflag = !!((req->cmd_flags & REQ_OP_MASK) == REQ_OP_WRITE);
#endif

    events.perf_submit(ctx, &data, sizeof(data));
    start.delete(&req);
    infobyreq.delete(&req);

    return 0;
}