1libtracefs(3) 2============= 3 4NAME 5---- 6tracefs_cpu_open, tracefs_cpu_close, tracefs_cpu_alloc_fd, tracefs_cpu_free_fd - Opening trace_pipe_raw data for reading 7 8SYNOPSIS 9-------- 10[verse] 11-- 12*#include <tracefs.h>* 13 14struct tracefs_cpu pass:[*]*tracefs_cpu_open*(struct tracefs_instance pass:[*]_instance_, 15 int _cpu_, bool _nonblock_); 16void *tracefs_cpu_close*(struct tracefs_cpu pass:[*]_tcpu_); 17 18struct tracefs_cpu pass:[*]*tracefs_cpu_alloc_fd*(int _fd_, int _subbuf_size_, bool _nonblock_); 19void *tracefs_cpu_free_fd*(struct tracefs_cpu pass:[*]_tcpu_); 20-- 21 22DESCRIPTION 23----------- 24This set of APIs can be used to open the raw data from the trace_pipe_raw 25files in the tracefs file system in oder to read them with the *tracefs_cpu_read*(3) 26functions. 27 28The *tracefs_cpu_open()* creates a descriptor that can read the tracefs 29trace_pipe_raw file for a given _cpu_ in a given _instance_. If _instance_ is 30NULL than the toplevel trace_pipe_raw file is used. 31 32The *tracefs_cpu_close()* closes all the file descriptors associated to the trace_pipe_raw 33opened by *tracefs_cpu_open()*. 34 35The *tracefs_cpu_alloc_fd()* will create a tracefs_cpu descriptor from an existing 36file descriptor _fd_. This is useful to use when connecting to a socket or pipe where 37the other end is feeding raw tracing data in the same format as the trace_pipe_raw 38file would (like in guest to host tracing). The caller is responsible for determining 39the _subbuf_size_ that will be used to break up the sub-buffers being read by the 40file descriptor. The _nonblock_ is treated the same as the same parameter in 41*tracefs_cpu_open()*. 42 43The *tracefs_cpu_free_fd()* is used to free the descriptor returned by *tracefs_cpu_alloc_fd()*. 44It does all the clean up that *tracefs_cpu_close()* performs, and that could also be 45used to free up the descriptor created by *tracefs_cpu_alloc_fd()* but will also close 46the file descriptor passed in. Note that *tracefs_cpu_free_fd()* should not be used 47on the descriptor returned by *tracefs_cpu_open()* as it will not close the file descriptor 48created by it. 49 50RETURN VALUE 51------------ 52The *tracefs_cpu_open()* returns a struct tracefs_cpu descriptor that can be 53used by the other functions or NULL on error. 54 55The *tracefs_cpu_alloc_fd()* returns a struct tracefs_cpu descriptor that can 56be used by the *tracefs_cpu_read*(3) related functions, where the descriptor 57will be reading the passed in _fd_ file descriptor. 58 59EXAMPLE 60------- 61See *tracefs_cpu_read*(3) for an example. 62 63FILES 64----- 65[verse] 66-- 67*tracefs.h* 68 Header file to include in order to have access to the library APIs. 69*-ltracefs* 70 Linker switch to add when building a program that uses the library. 71-- 72 73SEE ALSO 74-------- 75*libtracefs*(3), 76*libtraceevent*(3), 77*trace-cmd*(1) 78 79AUTHOR 80------ 81[verse] 82-- 83*Steven Rostedt* <[email protected]> 84-- 85REPORTING BUGS 86-------------- 87Report bugs to <[email protected]> 88 89LICENSE 90------- 91libtracefs is Free Software licensed under the GNU LGPL 2.1 92 93RESOURCES 94--------- 95https://git.kernel.org/pub/scm/libs/libtrace/libtracefs.git/ 96 97COPYING 98------- 99Copyright \(C) 2022 Google, Inc. Free use of this software is granted under 100the terms of the GNU Public License (GPL). 101