LIBTRACEEVENT(3)

NAME
tep_parse_saved_cmdlines, tep_parse_printk_formats, tep_parse_kallsyms, tep_parse_last_boot_info, tep_load_modules - Parsing functions to load mappings

SYNOPSIS

#include <event-parse.h>

int tep_parse_saved_cmdlines(struct tep_handle *tep, const char *buf);
int tep_parse_printk_formats(struct tep_handle *tep, const char *buf);
int tep_parse_kallsyms(struct tep_handle *tep, const char *buf);
int tep_parse_last_boot_info(struct tep_handle *tep, const char *lbi);
int tep_load_modules(struct tep_handle *tep, char *modules, size_t size);

DESCRIPTION

tep_parse_saved_cmdlines() is a helper function to parse content in the tracefs file system of the "saved_cmdlines" file (stored in a string buffer passed in by buf) and loads the mapping of the process IDs (pid) to the comm names in the tep handler. The events store the pid and this is used to be able to show the process names associated to those process ids. It parses the string buf that holds the content of saved_cmdlines and ends with a nul character (\0).

tep_parse_printk_formats() is a helper function to parse content in the tracefs file system of the "printk_formats" file (stored in a string buffer passed in by buf) and loads the mapping of addresses of strings that may be referenced by events. Events only store the address of constant strings in the kernel, and the mapping of their address to the string is exported to user space in the printk_formats file. It parses the string buf that holds the content of printk_formats and ends with a nul character (\0).

tep_parse_kallsyms() is a helper function to parse the Linux kernel /proc/kallsyms format (stored in a string buffer passed in by buf) and load the functions into the tep handler such that function IP addresses can be mapped to their name when parsing events with %pS in the print format field. It parses the string buf that holds the content of /proc/kallsyms and ends with a nul character (\0).

tep_parse_last_boot_info() loads information from the last_boot_info file of a persistent ring buffer instance. If a tracefs instance is declared as a persistent ring buffer and contains data from a previous boot, the last_boot_info file will have the addresses of the kernel as well as modules. It will use this information to base the function offsets in the binary buffer to match the function offsets in the kallsyms (loaded by tep_parse_kallsyms()) into the tep handler. The lbi is a nul terminated string that contains the content of the last_boot_info file from the persistent ring buffer instance.

tep_load_modules() loads the contents of the file /proc/modules into the tep handler. This will be used to match the modules found in the last_boot_info (loaded by tep_parse_last_boot_info()) to match the offsets of the binary data in in a persistent ring buffer that matches the address of a module from the previous boot to a module address found in modules. The modules parameter does not need to be nul terminated, but size is used to denote the size of the modules string. This function is useless if tep_parse_last_boot_info() isnt used.

RETURN VALUE

The tep_parse_saved_cmdlines() function returns 0 in case of success, or -1 in case of an error.

The tep_parse_printk_formats() function returns 0 in case of success, or -1 in case of an error.

The tep_parse_kallsyms() function returns 0 in case of success, or -1 in case of an error.

The tep_parse_last_boot_info() function retuns 0 in case of success, or -1 in case of error.

The tep_load_modules() function returns 0 in case of success, or -1 in case of error.

EXAMPLE

    ...
    #include <event-parse.h>
    #include <tracefs.h>
    #include <stdlib.h>

    int load_cmdlines(struct tep_handle *tep)
    {
            char *buf = NULL;
            int r;

            buf = tracefs_instance_file_read(NULL, "saved_cmdlines", NULL);
            if (!buf)
                    return -1;
            r = tep_parse_saved_cmdlines(tep, buf);
            free(buf);
            return r;
    }

    int load_print_strings(struct tep_handle *tep)
    {
            char *buf = NULL;
            int r;

            buf = tracefs_instance_file_read(NULL, "printk_formats", NULL);
            if (!buf)
                    return -1;
            r = tep_parse_printk_formats(tep, buf);
            free(buf);
            return r;
    }

    static char *read_file(const char *file, size_t *size)
    {
            FILE *fp;
            char *line = NULL;
            char *buf = NULL;
            size_t sz = 0;
            size_t len = 0;
            int r;

            fp = fopen(file, "r");
            while ((r = getline(&line, &sz, fp)) >= 0) {
                    buf = realloc(buf, len + r + 1);
                    memcpy(buf + len, line, r);
                    len += r;
            }
            free(line);
            fclose(fp);
            if (!buf)
                    return NULL;
            buf[len] = 0;
            *size = len;
            return buf;
    }

    int load_kallsyms(struct tep_handle *tep)
    {
            char *buf;
            size_t sz;
            int r;

            buf = read_file("/proc/kallsyms", &sz);
            if (!buf)
                    return -1;
            r = tep_parse_kallsyms(tep, buf);
            free(buf);
            return r;
    }

    int load_last_boot(struct tep_handle *tep, struct tracefs_instance *instance)
    {
            char *buf;
            size_t sz;
            int r;

            buf = tracefs_instance_file_read(instance, "last_boot_info", NULL);
            if (!buf)
                    return 0;

            r = tep_parse_last_boot_info(tep, buf);
            free(buf);
            if (r < 0)
                    return r;

            buf = read_file("/proc/modules", &sz);
            if (!buf)
                    return -1;
            r = tep_parse_kallsyms(tep, buf);
            free(buf);
            return r;
    }
    ...

FILES

    event-parse.h
            Header file to include in order to have access to the library APIs.
    -ltraceevent
            Linker switch to add when building a program that uses the library.

SEE ALSO

libtraceevent(3), trace-cmd(1), tep_register_comm(3), tep_register_function(3), tep_register_print_string(3)

AUTHOR

    Steven Rostedt <rostedt@goodmis.org[1]>, author of libtraceevent.
    Tzvetomir Stoyanov <tz.stoyanov@gmail.com[2]>, coauthor of libtraceevent.

REPORTING BUGS

Report bugs to <linux-trace-devel@vger.kernel.org[3]>

LICENSE

libtraceevent is Free Software licensed under the GNU LGPL 2.1

RESOURCES

https://git.kernel.org/pub/scm/libs/libtrace/libtraceevent.git/

NOTES

1.  rostedt@goodmis.org
    mailto:rostedt@goodmis.org

2.  tz.stoyanov@gmail.com
    mailto:tz.stoyanov@gmail.com

3.  linux-trace-devel@vger.kernel.org
    mailto:linux-trace-devel@vger.kernel.org