NAME

dt — dynamic tracer

SYNOPSIS

pseudo-device dt

DESCRIPTION

System and application tracing can happen in the kernel. It has to be configured and enabled through the ioctl(2) interface exposed by the pseudo-device /dev/dt.

This device can only be opened when the kern.allowdt sysctl(2) variable is set.

IOCTL INTERFACE

The ioctl(2) command codes below are defined in <dev/dt/dtvar.h>.

DTIOCGPLIST struct dtioc_probe *dtpr

Get available probe entries.

struct dtioc_probe {
	size_t		 	 dtpr_size;
	struct dtioc_probe_info	*dtpr_probes;
};

If dtpr_size is non-zero, as many probes as possible that can fit into this size will be copied into the supplied buffer. On exit, dtpr_size is always set to the total size required to hold all probe entries (i.e., it is set to sizeof(struct dtioc_probe_info) * dt_nprobes).

DTIOCGSTATS struct dtioc_stat *dtst

Get statistics for current recording.

struct dtioc_stat {
	uint64_t		 dtst_readevt;
	uint64_t		 dtst_dropevt;
};

DTIOCRECORD int on

Start or stop recording.

DTIOCPRBENABLE struct dtioc_req *dtrq

Enable the given probe for recording.

struct dtioc_req {
	uint32_t		 dtrq_pbn;
	struct dt_filter	 dtrq_filter;
	uint32_t		 dtrq_rate;
	uint64_t		 dtrq_evtflags;
};

FILES

/dev/dt: dynamic tracing device.

ERRORS

An open of /dev/dt will fail if:

[EPERM]: the kern.allowdt sysctl(2) variable wasn't set.
[ENOMEM]: not enough memory space was available.

HISTORY

The dt dynamic tracing mechanism first appeared in OpenBSD 6.7.