dcsnoop.bt

#!/usr/bin/env bpftrace
/*
 * dcsnoop	Trace directory entry cache (dcache) lookups.
 *		For Linux, uses bpftrace and eBPF.
 *
 * This uses kernel dynamic tracing of kernel functions, lookup_fast() and
 * d_lookup(), which will need to be modified to match kernel changes. See
 * code comments.
 *
 * USAGE: dcsnoop.bt
 *
 * Copyright 2018 Netflix, Inc.
 * Licensed under the Apache License, Version 2.0 (the "License")
 *
 * 08-Sep-2018	Brendan Gregg	Created this.
 */

#ifndef BPFTRACE_HAVE_BTF
#include <linux/fs.h>
#include <linux/sched.h>

// from fs/namei.c:
struct nameidata {
        struct path     path;
        struct qstr     last;
        // [...]
};
#endif

BEGIN
{
	printf("Tracing dcache lookups... Hit Ctrl-C to end.\n");
	printf("%-8s %-6s %-16s %1s %s\n", "TIME", "PID", "COMM", "T", "FILE");
}

// comment out this block to avoid showing hits:
kprobe:lookup_fast,
kprobe:lookup_fast.constprop.*
{
	$nd = (struct nameidata *)arg0;
	printf("%-8d %-6d %-16s R %s\n", elapsed / 1e6, pid, comm,
	    str($nd->last.name));
}

kprobe:d_lookup
{
	$name = (struct qstr *)arg1;
	@fname[tid] = $name->name;
}

kretprobe:d_lookup
/@fname[tid]/
{
	printf("%-8d %-6d %-16s M %s\n", elapsed / 1e6, pid, comm,
	    str(@fname[tid]));
	delete(@fname, tid);
}