Man page - tracecmd_read_at(3)

Packages contains this manual

Package:  trace-cmd
apt-get install trace-cmd

Manuals in package:
• tracecmd_follow_missed_events(3)
• trace-cmd-mem(1)
• trace-cmd(1)
• trace-cmd-hist(1)
• tracecmd_map_get_guest(3)
• trace-cmd-sqlhist(1)
• tracecmd_read_cpu_first(3)
• trace-cmd-convert(1)
• tracecmd_iterate_events(3)
• trace-cmd-check-events(1)
• trace-cmd-start(1)
• tracecmd_map_set_private(3)
• tracecmd_get_tsc2nsec(3)
• tracecmd_read_at(3)
• tracecmd_filter_add(3)
• trace-cmd-report(1)
• tracecmd_get_cpu_map(3)
• trace-cmd-profile(1)
• trace-cmd-set(1)
• trace-cmd-show(1)
• trace-cmd-dump(1)
• trace-cmd-snapshot(1)
• tracecmd_map_get_private(3)
• trace-cmd-stream(1)
• trace-cmd-clear(1)
• tracecmd_iterate_reset(3)
• trace-cmd-listen(1)
• tracecmd_iterate_events_multi(3)
• trace-cmd-list(1)
• tracecmd_open_fd(3)
• tracecmd_add_ts_offset(3)
• tracecmd_buffer_instance_name(3)
• tracecmd_get_private(3)
• tracecmd_map_get_host_pid(3)
• tracecmd_set_private(3)
• trace-cmd-options(1)
• tracecmd_buffer_instances(3)
• tracecmd_read_data(3)
• trace-cmd-attach(1)
• tracecmd_free_record(3)
• tracecmd_set_loglevel(3)
• tracecmd_get_first_ts(3)
• tracecmd_init_data(3)
• trace-cmd-stat(1)
• tracecmd_get_traceid(3)
• tracecmd_close(3)
• tracecmd_follow_event(3)
• trace-cmd-reset(1)
• tracecmd_open_head(3)
• tracecmd_map_find_by_host_pid(3)
• trace-cmd.dat.v7(5)
• trace-cmd-stack(1)
• trace-cmd-agent(1)
• tracecmd_map_vcpus(3)
• tracecmd_get_guest_cpumap(3)
• libtracecmd(3)
• trace-cmd-stop(1)
• trace-cmd.dat.v6(5)
• tracecmd_get_tep(3)
• trace-cmd-restore(1)
• trace-cmd-extract(1)
• tracecmd_buffer_instance_handle(3)
• trace-cmd-record(1)
• tracecmd_open(3)
• trace-cmd-split(1)
Documentations in package:
• trace-cmd

Manual

LIBTRACECMD

NAME
SYNOPSIS
DESCRIPTION
RETURN VALUE
EXAMPLE
FILES
SEE ALSO
AUTHOR
REPORTING BUGS
LICENSE
RESOURCES
COPYING
NOTES

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NAME

tracecmd_read_cpu_first, tracecmd_read_data, tracecmd_read_at, tracecmd_free_record, tracecmd_get_tep - Read recorded events from a trace file.

SYNOPSIS

#include <trace-cmd.h>

struct tep_record * tracecmd_read_cpu_first (struct tracecmd_input * handle , int cpu );
struct tep_record * tracecmd_read_data (struct tracecmd_input * handle , int cpu );
struct tep_record * tracecmd_read_at (struct tracecmd_input * handle , unsigned long long offset , int * cpu );
void tracecmd_free_record (struct tep_record * record );
struct tep_handle * tracecmd_get_tep (struct tracecmd_input * handle );

DESCRIPTION

This set of APIs can be used to read tracing data from a trace file opened with tracecmd_open()(3) , tracecmd_open_fd()(3) or tracecmd_open_head()(3) .

The tracecmd_read_cpu_first() function reads the first trace record for a given cpu from a trace file associated with handle . The returned record must be freed with tracecmd_free_record() .

The tracecmd_read_data() function reads the next trace record for a given cpu from a trace file associated with handle and increments the read location pointer, so that the next call to tracecmd_read_data() will not read the same record again. The returned record must be freed with tracecmd_free_record() .

The tracecmd_read_at() function reads a trace record from a specific offset within the file associated with handle . The CPU on which the recorded event occurred is stored in the cpu . The function does not change the current read location pointer. The returned record must be freed with tracecmd_free_record() .

The tracecmd_free_record() function frees a record returned by any of the tracecmd_read_ APIs.

The tracecmd_get_tep() function returns a tep context for a given handle .

RETURN VALUE

The tracecmd_read_cpu_first() , tracecmd_read_data() and tracecmd_read_at() functions return a pointer to struct tep_record or NULL in case of an error.The returned record must be freed with tracecmd_free_record() .

The tracecmd_get_tep() function returns a pointer to tep context or NULL if there is no tep context for the given handle . The returned tep pointer must not be freed.

EXAMPLE

#include <trace-cmd.h>
...
struct tracecmd_input *handle = tracecmd_open("trace.dat");
if (!handle) {
/* Failed to open trace.dat file */
}
...
unsigned long long offset = 0;
struct tep_record *rec;
int cpu = 0;
rec = tracecmd_read_cpu_first(handle, cpu);
while (rec) {
...
if ( /* some interesting record noticed */) {
/* store the offset of the interesting record */
offset = rec->offset;
}
...
tracecmd_free_record(rec);
rec = tracecmd_read_data(handle, cpu);
}
...
if (offset) {
rec = tracecmd_read_at(handle, offset, &cpu);
if (rec) {
/* Got record at offset on cpu */
...
tracecmd_free_record(rec);
}
}

...
tracecmd_close(hadle);

FILES

trace-cmd.h
Header file to include in order to have access to the library APIs.
-ltracecmd
Linker switch to add when building a program that uses the library.

SEE ALSO

libtracefs(3) , libtraceevent(3) , trace-cmd(1) trace-cmd.dat(5)

AUTHOR

Steven Rostedt < rostedt@goodmis.org [1] >
Tzvetomir Stoyanov < tz.stoyanov@gmail.com [2] >

REPORTING BUGS

Report bugs to < linux-trace-devel@vger.kernel.org [3] >

LICENSE

libtracecmd is Free Software licensed under the GNU LGPL 2.1

RESOURCES

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

COPYING

Copyright (C) 2020 VMware, 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

2.

tz.stoyanov@gmail.com

mailto:tz.stoyanov@gmail.com

3.

linux-trace-devel@vger.kernel.org

mailto:linux-trace-devel@vger.kernel.org

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