1libtracefs(3) 2============= 3 4NAME 5---- 6tracefs_cpu_open, tracefs_cpu_close, tracefs_cpu_alloc_fd, tracefs_cpu_free_fd, tracefs_cpu_snapshot_open - 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 21struct tracefs_cpu pass:[*]*tracefs_cpu_snapshot_open*(struct tracefs_instance pass:[*]_instance_, 22 int _cpu_, bool _nonblock_); 23-- 24 25DESCRIPTION 26----------- 27This set of APIs can be used to open the raw data from the trace_pipe_raw 28files in the tracefs file system in oder to read them with the *tracefs_cpu_read*(3) 29functions. 30 31The *tracefs_cpu_open()* creates a descriptor that can read the tracefs 32trace_pipe_raw file for a given _cpu_ in a given _instance_. If _instance_ is 33NULL than the toplevel trace_pipe_raw file is used. 34 35The *tracefs_cpu_close()* closes all the file descriptors associated to the trace_pipe_raw 36opened by *tracefs_cpu_open()*. 37 38The *tracefs_cpu_alloc_fd()* will create a tracefs_cpu descriptor from an existing 39file descriptor _fd_. This is useful to use when connecting to a socket or pipe where 40the other end is feeding raw tracing data in the same format as the trace_pipe_raw 41file would (like in guest to host tracing). The caller is responsible for determining 42the _subbuf_size_ that will be used to break up the sub-buffers being read by the 43file descriptor. The _nonblock_ is treated the same as the same parameter in 44*tracefs_cpu_open()*. 45 46The *tracefs_cpu_free_fd()* is used to free the descriptor returned by *tracefs_cpu_alloc_fd()*. 47It does all the clean up that *tracefs_cpu_close()* performs, and that could also be 48used to free up the descriptor created by *tracefs_cpu_alloc_fd()* but will also close 49the file descriptor passed in. Note that *tracefs_cpu_free_fd()* should not be used 50on the descriptor returned by *tracefs_cpu_open()* as it will not close the file descriptor 51created by it. 52 53The *tracefs_cpu_snapshot_open()* is similar to *tracefs_cpu_open()* except that it 54opens the snapshot buffer (see *tracefs_snapshot_snap*(3)). The snapshot buffer 55does not have a writer to it, it is only created by a snapshot action that swaps 56the current ring buffer with the snapshot buffer. The _nonblock_, when false, acts a little 57differently here too. Reads are not affected by the "buffer_percent" file. If the 58snapshot buffer is empty, it will block until a new snapshot happens. 59 60RETURN VALUE 61------------ 62The *tracefs_cpu_open()* and *tracefs_cpu_snapshot_open() both return a struct 63tracefs_cpu descriptor that can be used by the other functions or NULL on error. 64 65The *tracefs_cpu_alloc_fd()* returns a struct tracefs_cpu descriptor that can 66be used by the *tracefs_cpu_read*(3) related functions, where the descriptor 67will be reading the passed in _fd_ file descriptor. 68 69EXAMPLE 70------- 71See *tracefs_cpu_read*(3) for an example. 72 73FILES 74----- 75[verse] 76-- 77*tracefs.h* 78 Header file to include in order to have access to the library APIs. 79*-ltracefs* 80 Linker switch to add when building a program that uses the library. 81-- 82 83SEE ALSO 84-------- 85*libtracefs*(3), 86*libtraceevent*(3), 87*trace-cmd*(1) 88 89AUTHOR 90------ 91[verse] 92-- 93*Steven Rostedt* <rostedt@goodmis.org> 94-- 95REPORTING BUGS 96-------------- 97Report bugs to <linux-trace-devel@vger.kernel.org> 98 99LICENSE 100------- 101libtracefs is Free Software licensed under the GNU LGPL 2.1 102 103RESOURCES 104--------- 105https://git.kernel.org/pub/scm/libs/libtrace/libtracefs.git/ 106 107COPYING 108------- 109Copyright \(C) 2022 Google, Inc. Free use of this software is granted under 110the terms of the GNU Public License (GPL). 111