# trace-cmd.dat.v6

## NAME



           trace-cmd.dat.v6 - trace-cmd version 6 file format
    


## SYNOPSIS



           **trace-cmd.dat** ignore
    


## DESCRIPTION



           The trace-cmd(1) utility produces a "trace.dat" file. The file may
           also be named anything depending if the user specifies a different
           output name, but it must have a certain binary format. The file is
           used by trace-cmd to save kernel traces into it and be able to
           extract the trace from it at a later point (see
           trace-cmd-report(1)).
    


## INITIAL FORMAT



               The first three bytes contain the magic value:
    
               0x17 0x08  0x44
    
               The next 7 bytes contain the characters:
    
               "tracing"
    
               The next set of characters contain a null '\0' terminated string
               that contains the version of the file:
    
               "6\0"
    
               The next 1 byte contains the flags for the file endianess:
    
               0 = little endian
               1 = big endian
    
               The next byte contains the number of bytes per "long" value:
    
               4 - 32-bit long values
               8 - 64-bit long values
    
               Note: This is the long size of the target's userspace. Not the
               kernel space size.
    
               [ Now all numbers are written in file defined endianess. ]
    
               The next 4 bytes are a 32-bit word that defines what the traced
               host machine page size was.
    


## HEADER INFO FORMAT



               Directly after the initial format comes information about the
               trace headers recorded from the target box.
    
               The next 12 bytes contain the string:
    
               "header_page\0"
    
               The next 8 bytes are a 64-bit word containing the size of the
               page header information stored next.
    
               The next set of data is of the size read from the previous 8 bytes,
               and contains the data retrieved from debugfs/tracing/events/header_page.
    
               Note: The size of the second field \fBcommit\fR contains the target
               kernel long size. For example:
    
               field: local_t commit;        offset:8;       \fBsize:8;\fR   signed:1;
    
               shows the kernel has a 64-bit long.
    
               The next 13 bytes contain the string:
    
               "header_event\0"
    
               The next 8 bytes are a 64-bit word containing the size of the
               event header information stored next.
    
               The next set of data is of the size read from the previous 8 bytes
               and contains the data retrieved from debugfs/tracing/events/header_event.
    
               This data allows the trace-cmd tool to know if the ring buffer format
               of the kernel made any changes.
    


## FTRACE EVENT FORMATS



               Directly after the header information comes the information about
               the Ftrace specific events. These are the events used by the Ftrace plugins
               and are not enabled by the event tracing.
    
               The next 4 bytes contain a 32-bit word of the number of Ftrace event
               format files that are stored in the file.
    
               For the number of times defined by the previous 4 bytes is the
               following:
    
               8 bytes for the size of the Ftrace event format file.
    
               The Ftrace event format file copied from the target machine:
               debugfs/tracing/events/ftrace/<event>/format
    


## EVENT FORMATS



               Directly after the Ftrace formats comes the information about
               the event layout.
    
               The next 4 bytes are a 32-bit word containing the number of
               event systems that are stored in the file. These are the
               directories in debugfs/tracing/events excluding the \fBftrace\fR
               directory.
    
               For the number of times defined by the previous 4 bytes is the
               following:
    
               A null-terminated string containing the system name.
    
               4 bytes containing a 32-bit word containing the number
               of events within the system.
    
               For the number of times defined in the previous 4 bytes is the
               following:
    
               8 bytes for the size of the event format file.
    
               The event format file copied from the target machine:
               debugfs/tracing/events/<system>/<event>/format
    


## KALLSYMS INFORMATION



               Directly after the event formats comes the information of the mapping
               of function addresses to the function names.
    
               The next 4 bytes are a 32-bit word containing the size of the
               data holding the function mappings.
    
               The next set of data is of the size defined by the previous 4 bytes
               and contains the information from the target machine's file:
               /proc/kallsyms
    


## TRACE_PRINTK INFORMATION



               If a developer used trace_printk() within the kernel, it may
               store the format string outside the ring buffer.
               This information can be found in:
               debugfs/tracing/printk_formats
    
               The next 4 bytes are a 32-bit word containing the size of the
               data holding the printk formats.
    
               The next set of data is of the size defined by the previous 4 bytes
               and contains the information from debugfs/tracing/printk_formats.
    


## PROCESS INFORMATION



               Directly after the trace_printk formats comes the information mapping
               a PID to a process name.
    
               The next 8 bytes contain a 64-bit word that holds the size of the
               data mapping the PID to a process name.
    
               The next set of data is of the size defined by the previous 8 bytes
               and contains the information from debugfs/tracing/saved_cmdlines.
    


## REST OF TRACE-CMD HEADER



               Directly after the process information comes the last bit of the
               trace.dat file header.
    
               The next 4 bytes are a 32-bit word defining the number of CPUs that
               were discovered on the target machine (and has matching trace data
               for it).
    
               The next 10 bytes are one of the following:
    
               "options  \0"
    
               "latency  \0"
    
               "flyrecord\0"
    
               If it is "options  \0" then:
    
               The next 2 bytes are a 16-bit word defining the current option.
               If the the value is zero then there are no more options.
    
               Otherwise, the next 4 bytes contain a 32-bit word containing the
               option size. If the reader does not know how to handle the option
               it can simply skip it. Currently there are no options defined,
               but this is here to extend the data.
    
               The next option will be directly after the previous option, and
               the options ends with a zero in the option type field.
    
               The next 10 bytes after the options are one of the following:
    
               "latency  \0"
    
               "flyrecord\0"
    
               which would follow the same as if options were not present.
    
               If the value is "latency  \0", then the rest of the file is
               simply ASCII text that was taken from the target's:
               debugfs/tracing/trace
    
               If the value is "flyrecord\0", the following is present:
    
               For the number of CPUs that were read earlier, the
               following is present:
    
               8 bytes that are a 64-bit word containing the offset into the file
               that holds the data for the CPU.
    
               8 bytes that are a 64-bit word containing the size of the CPU
               data at that offset.
    


## CPU DATA



               The CPU data is located in the part of the file that is specified
               in the end of the header. Padding is placed between the header and
               the CPU data, placing the CPU data at a page aligned (target page) position
               in the file.
    
               This data is copied directly from the Ftrace ring buffer and is of the
               same format as the ring buffer specified by the event header files
               loaded in the header format file.
    
               The trace-cmd tool will try to \fBmmap(2)\fR the data page by page with the
               target's page size if possible. If it fails to mmap, it will just read the
               data instead.
    


## RESOURCES



           **https://git.kernel.org/pub/scm/utils/trace-cmd/trace-cmd.git/ **
    


## COPYING



           Copyright (C) 2010 Red Hat, Inc. Free use of this software is
           granted under the terms of the GNU Public License (GPL).
    


## NOTES



            1. rostedt@goodmis.org
               mailto:rostedt@goodmis.org
    


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