'\" t
.\"     Title: libtracefs
.\"    Author: [see the "AUTHOR" section]
.\" Generator: DocBook XSL Stylesheets vsnapshot <http://docbook.sf.net/>
.\"      Date: 07/25/2024
.\"    Manual: libtracefs Manual
.\"    Source: libtracefs 1.8.1
.\"  Language: English
.\"
.TH "LIBTRACEFS" "3" "07/25/2024" "libtracefs 1\&.8\&.1" "libtracefs Manual"
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.nh
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.\" * MAIN CONTENT STARTS HERE *
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.SH "NAME"
tracefs_event_get_file, tracefs_event_file_read, tracefs_event_file_write, tracefs_event_file_append, tracefs_event_file_clear, tracefs_event_file_exists \- Work with trace event files\&.
.SH "SYNOPSIS"
.sp
.nf
\fB#include <tracefs\&.h>\fR

char *\fBtracefs_event_get_file\fR(struct tracefs_instance *\fIinstance\fR, const char *\fIsystem\fR, const char *\fIevent\fR,
                             const char *\fIfile\fR);
char *\fBtracefs_event_file_read\fR(struct tracefs_instance *\fIinstance\fR, const char *\fIsystem\fR, const char *\fIevent\fR,
                              const char *\fIfile\fR, int *\fIpsize\fR);
int \fBtracefs_event_file_write\fR(struct tracefs_instance *\fIinstance\fR, const char *\fIsystem\fR, const char *\fIevent\fR,
                             const char *\fIfile\fR, const char *\fIstr\fR);
int \fBtracefs_event_file_append\fR(struct tracefs_instance *\fIinstance\fR, const char *\fIsystem\fR, const char *\fIevent\fR,
                              const char *\fIfile\fR, const char *\fIstr\fR);
int \fBtracefs_event_file_clear\fR(struct tracefs_instance *\fIinstance\fR, const char *\fIsystem\fR, const char *\fIevent\fR,
                             const char *\fIfile\fR);
bool \fBtracefs_event_file_exists\fR(struct tracefs_instance *\fIinstance\fR, const char *\fIsystem\fR, const char *\fIevent\fR,
                               const char *\fIfile\fR);
.fi
.SH "DESCRIPTION"
.sp
These are functions for accessing tracefs event specific files\&. These functions act similar to the tracefs instance file functions but are easier to get to if the system and events are known before hand\&.
.sp
The \fBtracefs_event_get_file()\fR returns the full path of the \fIfile\fR for the given \fIsystem\fR and \fIevent\fR that is within the given \fIinstance\fR\&. If \fIinstance\fR is NULL, then the file for the \fIevent\fR for the top level instance is returned\&. Note, there is no check to see if the file actually exists or even if the system and event exist\&. It only creates the path name for such an event if it did exist\&. This acts similar to the \fBtracefs_instance_get_file\fR(3), but is to be used to get to event files if the \fIsystem\fR and \fIevent\fR are already known\&.
.sp
The \fBtracefs_event_file_read()\fR reads the content for the \fIevent\fR \fIfile\fR for the given \fIinstance\fR or the top level instance if \fIinstance\fR is NULL\&. The content of the file is returned and \fIpsize\fR is set to the amount of data that was read\&. The returned content must be freed with \fBfree\fR(3)\&. This acts similar to the \fBtracefs_instance_file_read\fR(3), but is to be used to read the event file if the \fIsystem\fR and \fIevent\fR are already known\&.
.sp
The \fBtracefs_event_file_write()\fR writes \fIstr\fR to the \fIevent\fR \fIfile\fR\&. It will truncate anything that is already in that file\&. This acts similar to the \fBtracefs_instance_file_write\fR(3), but is to be used to read the event file if the \fIsystem\fR and \fIevent\fR are already known\&.
.sp
The \fBtracefs_event_file_append()\fR appends \fIstr\fR to the \fIevent\fR \fIfile\fR\&. It will not clear out the file as it writes \fIsting\fR\&. This acts similar to the \fBtracefs_instance_file_append\fR(3), but is to be used to read the event file if the \fIsystem\fR and \fIevent\fR are already known\&.
.sp
The \fBtracefs_event_file_clear()\fR clears the content of the \fIevent\fR \fIfile\fR\&. This acts similar to the \fBtracefs_instance_file_clear\fR(3), but is to be used to read the event file if the \fIsystem\fR and \fIevent\fR are already known\&.
.sp
The \fBtracefs_event_file_exists()\fR returns true if the \fIevent\fR \fIfile\fR exists, and false otherwise\&. This acts similar to the \fBtracefs_instance_file_exists\fR(3), but is to be used to read the event file if the \fIsystem\fR and \fIevent\fR are already known\&.
.SH "RETURN VALUE"
.sp
\fBtracefs_event_get_file()\fR returns the path of the given \fIsystem\fR/\fIevent\fR \fIfile\fR on success and NULL on error\&. The return value must be freed with \fBtracefs_put_tracing_file\fR(3)\&.
.sp
\fBtracefs_event_file_read()\fR reads the content of the \fIsystem\fR/\fIevent\fR \fIfile\fR or NULL on error\&. The return pointer must be freed with \fBfree\fR(3)\&.
.sp
\fBtracefs_event_file_write()\fR and \fBtracefs_event_file_append()\fR returns the number of bytes written to the \fIsystem\fR/\fIevent\fR \fIfile\fR or negative on error\&.
.sp
\fBtracefs_event_file_clear()\fR returns zero on success and \-1 on error\&.
.sp
\fBtracefs_event_file_exists()\fR returns true if the \fIsystem\fR/\fIevent\fR \fIfile\fR exists for the given \fIinstance\fR (or top level if \fIinstance\fR is NULL) or false otherwise\&.
.SH "EXAMPLE"
.sp
.if n \{\
.RS 4
.\}
.nf
#include <stdio\&.h>
#include <stdlib\&.h>
#include <unistd\&.h>
#include <tracefs\&.h>

int main(int argc, char **argv)
{
        char *system;
        char *event;
        char *file;
        char *cmd = NULL;
        char *buf;
        char *str;
        char ch = \*(Aqr\*(Aq;
        int size;

        if (argc < 4) {
                printf("usage: %s sytem event file [(\-a|\-w) write | \-c]\en"
                       "   reads the system/event file or writes if [write is supplied]\en",
                       argv[0]);
                exit(0);
        }

        system = argv[1];
        event = argv[2];
        file = argv[3];
        if (argc > 4)
                cmd = argv[4];

        if (!tracefs_event_file_exists(NULL, system, event, file)) {
                fprintf(stderr, "File %s/%s/%s does not exist\en",
                                system, event, file);
                exit(\-1);
        }

        if (cmd) {
                if (cmd[0] != \*(Aq\-\*(Aq)
                        ch = cmd[0];
                else
                        ch = cmd[1];
                if (!ch)
                        ch = \*(Aqc\*(Aq;
        }

        switch (ch) {
        case \*(Aqr\*(Aq:
                buf = tracefs_event_file_read(NULL, system, event, file, &size);
                if (buf)
                        printf("%s", buf);
                else
                        fprintf(stderr, "Failed to read %s/%s/%s\en",
                                system, event, file);
                free(buf);
                break;
        case \*(Aqw\*(Aq:
        case \*(Aqa\*(Aq:
                if (argc < 6) {
                        fprintf(stderr, "%s command requires something to write\en",
                                ch == \*(Aqw\*(Aq ? "write" : "append");
                        exit(\-1);
                }
                if (ch == \*(Aqw\*(Aq)
                        size = tracefs_event_file_write(NULL, system, event, file, argv[5]);
                else
                        size = tracefs_event_file_append(NULL, system, event, file, argv[5]);
                if (size < 0) {
                        fprintf(stderr, "Failed to write \*(Aq%s\*(Aq to %s/%s/%s\en",
                                        argv[5], system, event, file);
                        exit(\-1);
                }
                break;
        case \*(Aqc\*(Aq:
                if (tracefs_event_file_clear(NULL, system, event, file) < 0) {
                        fprintf(stderr, "Failed to clear %s/%s/%s\en",
                                system, event, file);
                        exit(\-1);
                }
                break;
        default:
                fprintf(stderr, "Unknown command \*(Aq%c\*(Aq\en", ch);
                exit(\-1);
        }
        exit(0);
}
.fi
.if n \{\
.RE
.\}
.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