'\" t
.\"     Title: libtracefs
.\"    Author: [see the "AUTHOR" section]
.\" Generator: DocBook XSL Stylesheets vsnapshot <http://docbook.sf.net/>
.\"      Date: 01/13/2024
.\"    Manual: libtracefs Manual
.\"    Source: libtracefs 1.8.0
.\"  Language: English
.\"
.TH "LIBTRACEFS" "3" "01/13/2024" "libtracefs 1\&.8\&.0" "libtracefs Manual"
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.SH "NAME"
tracefs_cpu_open, tracefs_cpu_close, tracefs_cpu_alloc_fd, tracefs_cpu_free_fd, tracefs_cpu_snapshot_open \- Opening trace_pipe_raw data for reading
.SH "SYNOPSIS"
.sp
.nf
\fB#include <tracefs\&.h>\fR

struct tracefs_cpu *\fBtracefs_cpu_open\fR(struct tracefs_instance *\fIinstance\fR,
                                     int \fIcpu\fR, bool \fInonblock\fR);
void \fBtracefs_cpu_close\fR(struct tracefs_cpu *\fItcpu\fR);

struct tracefs_cpu *\fBtracefs_cpu_alloc_fd\fR(int \fIfd\fR, int \fIsubbuf_size\fR, bool \fInonblock\fR);
void \fBtracefs_cpu_free_fd\fR(struct tracefs_cpu *\fItcpu\fR);

struct tracefs_cpu *\fBtracefs_cpu_snapshot_open\fR(struct tracefs_instance *\fIinstance\fR,
                                             int \fIcpu\fR, bool \fInonblock\fR);
.fi
.SH "DESCRIPTION"
.sp
This set of APIs can be used to open the raw data from the trace_pipe_raw files in the tracefs file system in oder to read them with the \fBtracefs_cpu_read\fR(3) functions\&.
.sp
The \fBtracefs_cpu_open()\fR creates a descriptor that can read the tracefs trace_pipe_raw file for a given \fIcpu\fR in a given \fIinstance\fR\&. If \fIinstance\fR is NULL than the toplevel trace_pipe_raw file is used\&.
.sp
The \fBtracefs_cpu_close()\fR closes all the file descriptors associated to the trace_pipe_raw opened by \fBtracefs_cpu_open()\fR\&.
.sp
The \fBtracefs_cpu_alloc_fd()\fR will create a tracefs_cpu descriptor from an existing file descriptor \fIfd\fR\&. This is useful to use when connecting to a socket or pipe where the other end is feeding raw tracing data in the same format as the trace_pipe_raw file would (like in guest to host tracing)\&. The caller is responsible for determining the \fIsubbuf_size\fR that will be used to break up the sub\-buffers being read by the file descriptor\&. The \fInonblock\fR is treated the same as the same parameter in \fBtracefs_cpu_open()\fR\&.
.sp
The \fBtracefs_cpu_free_fd()\fR is used to free the descriptor returned by \fBtracefs_cpu_alloc_fd()\fR\&. It does all the clean up that \fBtracefs_cpu_close()\fR performs, and that could also be used to free up the descriptor created by \fBtracefs_cpu_alloc_fd()\fR but will also close the file descriptor passed in\&. Note that \fBtracefs_cpu_free_fd()\fR should not be used on the descriptor returned by \fBtracefs_cpu_open()\fR as it will not close the file descriptor created by it\&.
.sp
The \fBtracefs_cpu_snapshot_open()\fR is similar to \fBtracefs_cpu_open()\fR except that it opens the snapshot buffer (see \fBtracefs_snapshot_snap\fR(3))\&. The snapshot buffer does not have a writer to it, it is only created by a snapshot action that swaps the current ring buffer with the snapshot buffer\&. The \fInonblock\fR, when false, acts a little differently here too\&. Reads are not affected by the "buffer_percent" file\&. If the snapshot buffer is empty, it will block until a new snapshot happens\&.
.SH "RETURN VALUE"
.sp
The \fBtracefs_cpu_open()\fR and *tracefs_cpu_snapshot_open() both return a struct tracefs_cpu descriptor that can be used by the other functions or NULL on error\&.
.sp
The \fBtracefs_cpu_alloc_fd()\fR returns a struct tracefs_cpu descriptor that can be used by the \fBtracefs_cpu_read\fR(3) related functions, where the descriptor will be reading the passed in \fIfd\fR file descriptor\&.
.SH "EXAMPLE"
.sp
See \fBtracefs_cpu_read\fR(3) for an example\&.
.SH "FILES"
.sp
.if n \{\
.RS 4
.\}
.nf
\fBtracefs\&.h\fR
        Header file to include in order to have access to the library APIs\&.
\fB\-ltracefs\fR
        Linker switch to add when building a program that uses the library\&.
.fi
.if n \{\
.RE
.\}
.SH "SEE ALSO"
.sp
\fBlibtracefs\fR(3), \fBlibtraceevent\fR(3), \fBtrace\-cmd\fR(1)
.SH "AUTHOR"
.sp
.if n \{\
.RS 4
.\}
.nf
\fBSteven Rostedt\fR <\m[blue]\fBrostedt@goodmis\&.org\fR\m[]\&\s-2\u[1]\d\s+2>
.fi
.if n \{\
.RE
.\}
.SH "REPORTING BUGS"
.sp
Report bugs to <\m[blue]\fBlinux\-trace\-devel@vger\&.kernel\&.org\fR\m[]\&\s-2\u[2]\d\s+2>
.SH "LICENSE"
.sp
libtracefs is Free Software licensed under the GNU LGPL 2\&.1
.SH "RESOURCES"
.sp
\m[blue]\fBhttps://git\&.kernel\&.org/pub/scm/libs/libtrace/libtracefs\&.git/\fR\m[]
.SH "COPYING"
.sp
Copyright (C) 2022 Google, Inc\&. Free use of this software is granted under the terms of the GNU Public License (GPL)\&.
.SH "NOTES"
.IP " 1." 4
rostedt@goodmis.org
.RS 4
\%mailto:rostedt@goodmis.org
.RE
.IP " 2." 4
linux-trace-devel@vger.kernel.org
.RS 4
\%mailto:linux-trace-devel@vger.kernel.org
.RE