BTRACE(8)

NAME
btrace - block-level tracing interface

SYNOPSIS
btrace start device entries

btrace stop device file

btrace reset device

btrace dump file

DESCRIPTION
The btrace tool is the user interface to MINIX3's block-level tracing facility. It allows one to start, stop, and reset tracing, and dump a trace output file in a somewhat human-readable format.

COMMANDS

start
    This command starts tracing all block requests on the given device. Each block request takes up one entry in the log. The entries parameter specifies the allocation side of the log in the driver process, in number of (32-byte) entries. Once the log is full, no more entries will be added.

stop
    This command stops tracing on the given device, and dumps the resulting log to the given output file.

reset
    This command stops tracing on the given device and resets the state of the block tracer. This should be useful only in emergency situations.

dump
    Dump the contents of a log file generated earlier with btrace stop, in human-readable format. Heavy users of the block tracing facility will probably want to write their own tools for parsing and visualizing dump files.

LIMITATIONS
Only one block device can be traced per driver at once. It is therefore also not possible to trace a device and all its partitions at the same time. The tracing facility has been designed for tracing activity of a single file system, in which case these limitations are not important.

The log will always start with a close operation on the device, since btrace closes the file descriptor used to instruct the driver to start tracing. Similarly, for logs that have not already filled up during tracing, the last entry will be a btrace-triggered open operation.

EXAMPLES

btrace start /dev/c2d0 10240
    # Start a block trace on c2d0.

btrace stop /dev/c2d0 outfile
    # Stop the block trace on c2d0.

btrace dump outfile
    # View the output of the trace.

SEE ALSO
ioctl(2).

AUTHOR
David van Moolenbroek <david@minix3.org>