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NAME |SYNOPSIS |DESCRIPTION |RETURN VALUE |EXAMPLE |FILES |SEE ALSO |AUTHOR |REPORTING BUGS |LICENSE |RESOURCES |COPYING |NOTES |COLOPHON | |
LIBTRACEFS(3) libtracefs ManualLIBTRACEFS(3)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
#include <tracefs.h> struct tracefs_cpu *tracefs_cpu_open(struct tracefs_instance *instance, intcpu, boolnonblock); voidtracefs_cpu_close(struct tracefs_cpu *tcpu); struct tracefs_cpu *tracefs_cpu_alloc_fd(intfd, intsubbuf_size, boolnonblock); voidtracefs_cpu_free_fd(struct tracefs_cpu *tcpu); struct tracefs_cpu *tracefs_cpu_snapshot_open(struct tracefs_instance *instance, intcpu, boolnonblock);
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 thetracefs_cpu_read(3) functions. Thetracefs_cpu_open()creates a descriptor that can read the tracefs trace_pipe_raw file for a givencpu in a giveninstance. Ifinstance is NULL than the toplevel trace_pipe_raw file is used. Thetracefs_cpu_close()closes all the file descriptors associated to the trace_pipe_raw opened bytracefs_cpu_open(). Thetracefs_cpu_alloc_fd()will create a tracefs_cpu descriptor from an existing file descriptorfd. 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 thesubbuf_size that will be used to break up the sub-buffers being read by the file descriptor. Thenonblock is treated the same as the same parameter intracefs_cpu_open(). Thetracefs_cpu_free_fd()is used to free the descriptor returned bytracefs_cpu_alloc_fd(). It does all the clean up thattracefs_cpu_close()performs, and that could also be used to free up the descriptor created bytracefs_cpu_alloc_fd()but will also close the file descriptor passed in. Note thattracefs_cpu_free_fd()should not be used on the descriptor returned bytracefs_cpu_open()as it will not close the file descriptor created by it. Thetracefs_cpu_snapshot_open()is similar totracefs_cpu_open() except that it opens the snapshot buffer (seetracefs_snapshot_snap(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. Thenonblock, 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.
Thetracefs_cpu_open()and *tracefs_cpu_snapshot_open() both return a struct tracefs_cpu descriptor that can be used by the other functions or NULL on error. Thetracefs_cpu_alloc_fd()returns a struct tracefs_cpu descriptor that can be used by thetracefs_cpu_read(3) related functions, where the descriptor will be reading the passed infd file descriptor.
Seetracefs_cpu_read(3) for an example.
tracefs.h Header file to include in order to have access to the library APIs.-ltracefs Linker switch to add when building a program that uses the library.
libtracefs(3),libtraceevent(3),trace-cmd(1)
Steven Rostedt<rostedt@goodmis.org[1]>
Report bugs to <linux-trace-devel@vger.kernel.org[2]>
libtracefs is Free Software licensed under the GNU LGPL 2.1
https://git.kernel.org/pub/scm/libs/libtrace/libtracefs.git/
Copyright (C) 2022 Google, Inc. Free use of this software is granted under the terms of the GNU Public License (GPL).
1. rostedt@goodmis.org mailto:rostedt@goodmis.org 2. linux-trace-devel@vger.kernel.org mailto:linux-trace-devel@vger.kernel.org
This page is part of thelibtracefs (Linux kernel trace file system library) project. Information about the project can be found at ⟨https://www.trace-cmd.org/⟩. If you have a bug report for this manual page, see ⟨https://www.trace-cmd.org/⟩. This page was obtained from the project's upstream Git repository ⟨https://git.kernel.org/pub/scm/libs/libtrace/libtracefs.git⟩ on 2025-08-11. (At that time, the date of the most recent commit that was found in the repository was 2025-06-02.) If you discover any rendering problems in this HTML version of the page, or you believe there is a better or more up-to-date source for the page, or you have corrections or improvements to the information in this COLOPHON (which isnot part of the original manual page), send a mail to man-pages@man7.orglibtracefs 1.8.1 01/02/2025LIBTRACEFS(3)Pages that refer to this page:tracefs_cpu_open_mapped(3), tracefs_cpu_read_buf(3), tracefs_cpu_read_size(3)
HTML rendering created 2025-09-06 byMichael Kerrisk, author ofThe Linux Programming Interface. For details of in-depthLinux/UNIX system programming training courses that I teach, lookhere. Hosting byjambit GmbH. | |