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| -rw-r--r-- | Documentation/libtracefs-cpu.txt | 240 |
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diff --git a/Documentation/libtracefs-cpu.txt b/Documentation/libtracefs-cpu.txt new file mode 100644 index 0000000..d6215d9 --- /dev/null +++ b/Documentation/libtracefs-cpu.txt @@ -0,0 +1,240 @@ +libtracefs(3) +============= + +NAME +---- +tracefs_cpu_read_size, tracefs_cpu_read, tracefs_cpu_buffered_read, tracefs_cpu_write, +tracefs_cpu_stop, tracefs_cpu_flush, tracefs_cpu_flush_write, tracefs_cpu_pipe +- Reading trace_pipe_raw data + +SYNOPSIS +-------- +[verse] +-- +*#include <tracefs.h>* + +int *tracefs_cpu_read_size*(struct tracefs_cpu pass:[*]_tcpu_); +int *tracefs_cpu_read*(struct tracefs_cpu pass:[*]_tcpu_, void pass:[*]_buffer_, bool _nonblock_); +int *tracefs_cpu_buffered_read*(struct tracefs_cpu pass:[*]_tcpu_, void pass:[*]_buffer_, bool _nonblock_); +int *tracefs_cpu_write*(struct tracefs_cpu pass:[*]_tcpu_, int _wfd_, bool _nonblock_); +int *tracefs_cpu_stop*(struct tracefs_cpu pass:[*]_tcpu_); +int *tracefs_cpu_flush*(struct tracefs_cpu pass:[*]_tcpu_, void pass:[*]_buffer_); +int *tracefs_cpu_flush_write*(struct tracefs_cpu pass:[*]_tcpu_, int _wfd_); +int *tracefs_cpu_pipe*(struct tracefs_cpu pass:[*]_tcpu_, int _wfd_, bool _nonblock_); +-- + +DESCRIPTION +----------- +This set of APIs can be used to read the raw data from the trace_pipe_raw +files in the tracefs file system. + +The *tracefs_cpu_read_size()* returns the subbuffer size of the trace_pipe_raw. This +returns the minimum size of the buffer that is passed to the below functions. + +The *tracefs_cpu_read()* reads the trace_pipe_raw files associated to _tcpu_ into _buffer_. +_buffer_ must be at least the size of the sub buffer of the ring buffer, +which is returned by *tracefs_cpu_read_size()*. If _nonblock_ is set, and +there's no data available, it will return immediately. Otherwise depending +on how _tcpu_ was opened, it will block. If _tcpu_ was opened with nonblock +set, then this _nonblock_ will make no difference. + +The *tracefs_cpu_buffered_read()* is basically the same as *tracefs_cpu_read()* +except that it uses a pipe through splice to buffer reads. This will batch +reads keeping the reading from the ring buffer less intrusive to the system, +as just reading all the time can cause quite a disturbance. Note, one +difference between this and *tracefs_cpu_read()* is that it will read only in +sub buffer pages. If the ring buffer has not filled a page, then it will not +return anything, even with _nonblock_ set. Calls to *tracefs_cpu_flush()* +should be done to read the rest of the file at the end of the trace. + +The *tracefs_cpu_write()* will pipe the data from the trace_pipe_raw +file associated with _tcpu_ into the _wfd_ file descriptor. If _nonblock_ is set, +then it will not block on if there's nothing to write. Note, it will only write +sub buffer size data to _wfd_. Calls to tracefs_cpu_flush_write() are needed to +write out the rest. + +The *tracefs_cpu_stop()* will attempt to unblock a task blocked on _tcpu_ reading it. +On older kernels, it may not do anything for the pipe reads, as older kernels do not +wake up tasks waiting on the ring buffer. Returns 0 if it definitely woke up any possible +waiters, but returns 1 if it is not sure it worked and waiters may need to have a signal +sent to them. + +The *tracefs_cpu_flush()* reads the trace_pipe_raw file associated by the _tcpu_ and puts it +into _buffer_, which must be the size of the sub buffer which is retrieved. +by *tracefs_cpu_read_size()*. This should be called at the end of tracing +to get the rest of the data. This call will convert the file descriptor of +trace_pipe_raw into non-blocking mode. + +The *tracefs_cpu_flush_write()* same as *trace_cpu_flush()* except it takes a file +descriptor _wfd_ to flush the data into. + +The *tracefs_cpu_pipe()* is similar to *tracefs_cpu_write()* but the _wfd_ file descriptor +must be a pipe. This call is an optimization of *tracefs_cpu_write()* that uses two calls +to *splice*(2) in order to connect the trace_pipe_raw file descriptor with the write file +descriptor. *splice*(2) requires that one of the passed in file descriptors is a pipe. +If the application wants to pass the data to an existing pipe, there's no reason for +there to be two *splice*(2) system calls and *tracefs_cpu_pipe()* can simply use a single +call to _wfd_. + +RETURN VALUE +------------ +The *tracefs_cpu_open()* returns a struct tracefs_cpu descriptor that can be +used by the other functions or NULL on error. + +The *tracefs_cpu_read_size()* returns the minimum size of the buffers to be +used with *tracefs_cpu_read()*, *tracefs_cpu_buffered_read()* and *tracefs_cpu_flush()*. +Returns negative on error. + +The *tracefs_cpu_read()* returns the number of bytes read, or negative on error. + +The *tracefs_cpu_buffered_read()* returns the number of bytes read or negative on error. + +The *tracefs_cpu_write()* returns the number of bytes written to the file +or negative on error. + +The *tracefs_cpu_stop()* returns zero if any waiters were guaranteed to be +woken up from waiting on input, or returns one if this is an older kernel +that does not supply that guarantee, and a signal may need to be sent to +any waiters. Returns negative on error. + +The *tracefs_cpu_flush()* returns the number of bytes read or negative on error. + +The *tracefs_cpu_flush_write()* returns the number of bytes written to the +file or negative on error. + +EXAMPLE +------- +[source,c] +-- +#define _LARGEFILE64_SOURCE +#include <stdlib.h> +#include <ctype.h> +#include <pthread.h> +#include <unistd.h> +#include <tracefs.h> + +struct thread_data { + struct tracefs_cpu *tcpu; + int done; + int fd; +}; + +static void *thread_run(void *arg) +{ + struct thread_data *data = arg; + struct tracefs_cpu *tcpu = data->tcpu; + int fd = data->fd; + int ret; + + while (!data->done) { + ret = tracefs_cpu_write(tcpu, fd, false); + printf("wrote %d\n", ret); + } + return NULL; +} + +int main (int argc, char **argv) +{ + struct tracefs_instance *instance; + struct thread_data data; + pthread_t thread; + char *file; + int secs = 10; + int cpu; + int ret; + + if (argc < 3 || !isdigit(argv[1][0])) { + printf("usage: %s cpu file_destination [sleep secs]\n\n", argv[0]); + exit(-1); + } + + cpu = atoi(argv[1]); + file = argv[2]; + + if (argc > 3) + secs = atoi(argv[3]); + + instance = tracefs_instance_create("cpu_write"); + if (!instance) { + perror("create instance"); + exit(-1); + } + + memset(&data, 0, sizeof(data)); + + data.tcpu = tracefs_cpu_open(instance, cpu, 0); + if (!data.tcpu) { + perror("Open instance"); + exit(-1); + } + + data.fd = open(file, O_WRONLY | O_CREAT | O_TRUNC | O_LARGEFILE, 0644); + if (data.fd < 0) { + perror(file); + exit(-1); + } + + pthread_create(&thread, NULL, thread_run, &data); + + sleep(secs); + + data.done = 1; + printf("stopping\n"); + ret = tracefs_cpu_stop(data.tcpu); + + printf("joining %d\n", ret); + pthread_join(thread, NULL); + + tracefs_trace_off(instance); + do { + ret = tracefs_cpu_flush_write(data.tcpu, data.fd); + printf("flushed %d\n", ret); + } while (ret > 0); + tracefs_trace_on(instance); + + tracefs_cpu_close(data.tcpu); + close(data.fd); + + return 0; +} +-- +FILES +----- +[verse] +-- +*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. +-- + +SEE ALSO +-------- +*tracefs_cpu_open*(3) +*tracefs_cpu_close*(3) +*libtracefs*(3), +*libtraceevent*(3), +*trace-cmd*(1) + +AUTHOR +------ +[verse] +-- +*Steven Rostedt* <rostedt@goodmis.org> +-- +REPORTING BUGS +-------------- +Report bugs to <linux-trace-devel@vger.kernel.org> + +LICENSE +------- +libtracefs is Free Software licensed under the GNU LGPL 2.1 + +RESOURCES +--------- +https://git.kernel.org/pub/scm/libs/libtrace/libtracefs.git/ + +COPYING +------- +Copyright \(C) 2022 Google, Inc. Free use of this software is granted under +the terms of the GNU Public License (GPL). |