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+libtracefs(3)
+=============
+
+NAME
+----
+tracefs_sql - Create a synthetitc event via an SQL statement
+
+SYNOPSIS
+--------
+[verse]
+--
+*#include <tracefs.h>*
+
+struct tracefs_synth *tracefs_sql(struct tep_handle pass:[*]tep, const char pass:[*]name,
+ const char pass:[*]sql_buffer, char pass:[**]err);
+--
+
+DESCRIPTION
+-----------
+Synthetic events are dynamically created events that attach two existing events
+together via one or more matching fields between the two events. It can be used
+to find the latency between the events, or to simply pass fields of the first event
+on to the second event to display as one event.
+
+The Linux kernel interface to create synthetic events is complex, and there needs
+to be a better way to create synthetic events that is easy and can be understood
+via existing technology.
+
+If you think of each event as a table, where the fields are the column of the table
+and each instance of the event as a row, you can understand how SQL can be used
+to attach two events together and for another event (table). Utilizing the
+SQL *SELECT* *FROM* *JOIN* *ON* [ *WHERE* ] syntax, a synthetic event can easily
+be created from two different events.
+
+
+*tracefs_sql*() takes in a *tep* handler (See _tep_local_events_(3)) that is used to
+verify the events within the _sql_buffer_ expression. The _name_ is the name of the
+synthetic event to create. If _err_ points to an address of a string, it will be filled
+with a detailed message on any type of parsing error, including fields that do not belong
+to an event, or if the events or fields are not properly compared.
+
+The example program below is a fully functional parser where it will create a synthetic
+event from a SQL syntax passed in via the command line or a file.
+
+The SQL format is as follows:
+
+*SELECT* <fields> FROM <start-event> JOIN <end-event> ON <matching-fields> WHERE <filter>
+
+Note, although the examples show the SQL commands in uppercase, they are not required to
+be so. That is, you can use "SELECT" or "select" or "sElEct".
+
+For example:
+[source,c]
+--
+SELECT syscalls.sys_enter_read.fd, syscalls.sys_exit_read.ret FROM syscalls.sys_enter_read
+ JOIN syscalls.sys_exit_read
+ ON syscalls.sys_enter_read.common_pid = syscalls.sys_exit_write.common_pid
+--
+
+Will create a synthetic event that with the fields:
+
+ u64 fd; s64 ret;
+
+Because the function takes a _tep_ handle, and usually all event names are unique, you can
+leave off the system (group) name of the event, and *tracefs_sql*() will discover the
+system for you.
+
+That is, the above statement would work with:
+
+[source,c]
+--
+SELECT sys_enter_read.fd, sys_exit_read.ret FROM sys_enter_read JOIN sys_exit_read
+ ON sys_enter_read.common_pid = sys_exit_write.common_pid
+--
+
+The *AS* keyword can be used to name the fields as well as to give an alias to the
+events, such that the above can be simplified even more as:
+
+[source,c]
+--
+SELECT start.fd, end.ret FROM sys_enter_read AS start JOIN sys_exit_read AS end ON start.common_pid = end.common_pid
+--
+
+The above aliases _sys_enter_read_ as *start* and _sys_exit_read_ as *end* and uses
+those aliases to reference the event throughout the statement.
+
+Using the *AS* keyword in the selection portion of the SQL statement will define what
+those fields will be called in the synthetic event.
+
+[source,c]
+--
+SELECT start.fd AS filed, end.ret AS return FROM sys_enter_read AS start JOIN sys_exit_read AS end
+ ON start.common_pid = end.common_pid
+--
+
+The above labels the _fd_ of _start_ as *filed* and the _ret_ of _end_ as *return* where
+the synthetic event that is created will now have the fields:
+
+ u64 filed; s64 return;
+
+The fields can also be calculated with results passed to the synthetic event:
+
+[source,c]
+--
+select start.truesize, end.len, (start.truesize - end.len) as diff from napi_gro_receive_entry as start
+ JOIN netif_receive_skb as end ON start.skbaddr = end.skbaddr
+--
+
+Which would show the *truesize" of the _napi_gro_receive_entry_ event, the actual
+_len_ of the content, shown by the _netif_receive_skb_, and alse the delta between
+the two and expressed by the field *diff*.
+
+The code also supports recording the timestamps at either event, and performing calculations
+on them. For wakeup latency, you have:
+
+[source,c]
+--
+select start.pid, (end.TIMESTAMP_USECS - start.TIMESTAMP_USECS) as lat from sched_waking as start
+ JOIN sched_switch as end ON start.pid = end.next_pid
+--
+
+The above will create a synthetic event that records the _pid_ of the task being woken up,
+and the time difference between the _sched_waking_ event and the _sched_switch_ event.
+The *TIMESTAMP_USECS* will truncate the time down to microseconds as the timestamp usually
+recorded in the tracing buffer has nanosecond resolution. If you do not want that
+truncation, use *TIMESTAMP* instead of *TIMESTAMP_USECS*.
+
+Finally, the *WHERE* clause can be added, that will let you add filters on either or both events.
+
+[source,c]
+--
+select start.pid, (end.TIMESTAMP_USECS - start.TIMESTAMP_USECS) as lat from sched_waking as start
+ JOIN sched_switch as end ON start.pid = end.next_pid
+ WHERE start.prio < 100 && (!(end.prev_pid < 1 || end.prev_prio > 100) || end.prev_pid == 0)
+--
+
+*NOTE*
+
+Although both events can be used together in the *WHERE* clause, they must not be mixed outside
+the top most "&&" statements. You can not OR (||) the events together, where a filter of one
+event is OR'd to a filter of the other event. This does not make sense, as the synthetic event
+requires both events to take place to be recorded. If one is filtered out, then the synthetic
+event does not execute.
+
+[source,c]
+--
+select start.pid, (end.TIMESTAMP_USECS - start.TIMESTAMP_USECS) as lat from sched_waking as start
+ JOIN sched_switch as end ON start.pid = end.next_pid
+ WHERE start.prio < 100 && end.prev_prio < 100
+--
+
+The above is valid.
+
+Where as the below is not.
+
+[source,c]
+--
+select start.pid, (end.TIMESTAMP_USECS - start.TIMESTAMP_USECS) as lat from sched_waking as start
+ JOIN sched_switch as end ON start.pid = end.next_pid
+ WHERE start.prio < 100 || end.prev_prio < 100
+--
+
+
+RETURN VALUE
+------------
+Returns 0 on success and -1 on failure. On failure, if _err_ is defined, it will be
+allocated to hold a detailed description of what went wrong if it the error was caused
+by a parsing error, or that an event, field does not exist or is not compatible with
+what it was combined with.
+
+EXAMPLE
+-------
+[source,c]
+--
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdarg.h>
+#include <string.h>
+#include <errno.h>
+#include <unistd.h>
+#include <tracefs.h>
+
+static void usage(char **argv)
+{
+ fprintf(stderr, "usage: %s [-ed][-n name][-t dir][-f file | sql-command-line]\n"
+ " -n name - name of synthetic event 'Anonymous' if left off\n"
+ " -t dir - use dir instead of /sys/kernel/tracing\n"
+ " -e - execute the commands to create the synthetic event\n"
+ " -d - delete the synthetic event that would be created\n"
+ " -f file - read sql lines from file otherwise from the command line\n"
+ " if file is '-' then read from standard input.\n",
+ argv[0]);
+ exit(-1);
+}
+
+static int do_sql(const char *buffer, const char *name,
+ const char *trace_dir, bool execute)
+{
+ struct tracefs_synth *synth;
+ struct tep_handle *tep;
+ struct trace_seq seq;
+ char *err;
+
+ if (!name)
+ name = "Anonymous";
+
+ trace_seq_init(&seq);
+ tep = tracefs_local_events(trace_dir);
+ if (!tep) {
+ if (!trace_dir)
+ trace_dir = "tracefs directory";
+ perror(trace_dir);
+ exit(-1);
+ }
+
+ synth = tracefs_sql(tep, name, buffer, &err);
+ if (!synth) {
+ perror("Failed creating synthetic event!");
+ if (err)
+ fprintf(stderr, "%s", err);
+ exit(-1);
+ }
+
+ tracefs_synth_show(&seq, NULL, synth);
+ if (execute)
+ tracefs_synth_create(NULL, synth);
+ tracefs_synth_free(synth);
+
+ trace_seq_do_printf(&seq);
+ trace_seq_destroy(&seq);
+ return 0;
+}
+
+int main (int argc, char **argv)
+{
+ char *trace_dir = NULL;
+ char *buffer = NULL;
+ char buf[BUFSIZ];
+ int buffer_size = 0;
+ const char *file = NULL;
+ bool execute = false;
+ const char *name;
+ FILE *fp;
+ size_t r;
+ int c;
+ int i;
+
+ for (;;) {
+ c = getopt(argc, argv, "ht:f:edn:");
+ if (c == -1)
+ break;
+
+ switch(c) {
+ case 'h':
+ usage(argv);
+ case 't':
+ trace_dir = optarg;
+ break;
+ case 'f':
+ file = optarg;
+ break;
+ case 'e':
+ execute = true;
+ break;
+ case 'n':
+ name = optarg;
+ break;
+ }
+ }
+
+ if (file) {
+ if (!strcmp(file, "-"))
+ fp = stdin;
+ else
+ fp = fopen(file, "r");
+ if (!fp) {
+ perror(file);
+ exit(-1);
+ }
+ while ((r = fread(buf, 1, BUFSIZ, fp)) > 0) {
+ buffer = realloc(buffer, buffer_size + r + 1);
+ strncpy(buffer + buffer_size, buf, r);
+ buffer_size += r;
+ }
+ fclose(fp);
+ if (buffer_size)
+ buffer[buffer_size] = '\0';
+ } else if (argc == optind) {
+ usage(argv);
+ } else {
+ for (i = optind; i < argc; i++) {
+ r = strlen(argv[i]);
+ buffer = realloc(buffer, buffer_size + r + 2);
+ if (i != optind)
+ buffer[buffer_size++] = ' ';
+ strcpy(buffer + buffer_size, argv[i]);
+ buffer_size += r;
+ }
+ }
+
+ do_sql(buffer, name, trace_dir, execute);
+ free(buffer);
+
+ 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
+--------
+_libtracefs(3)_,
+_libtraceevent(3)_,
+_trace-cmd(1)_,
+_tracefs_synth_init(3)_,
+_tracefs_synth_add_match_field(3)_,
+_tracefs_synth_add_compare_field(3)_,
+_tracefs_synth_add_start_field(3)_,
+_tracefs_synth_add_end_field(3)_,
+_tracefs_synth_append_start_filter(3)_,
+_tracefs_synth_append_end_filter(3)_,
+_tracefs_synth_create(3)_,
+_tracefs_synth_destroy(3)_,
+_tracefs_synth_free(3)_,
+_tracefs_synth_show(3)_,
+_tracefs_hist_alloc(3)_,
+_tracefs_hist_free(3)_,
+_tracefs_hist_add_key(3)_,
+_tracefs_hist_add_value(3)_,
+_tracefs_hist_add_name(3)_,
+_tracefs_hist_start(3)_,
+_tracefs_hist_destory(3)_,
+_tracefs_hist_add_sort_key(3)_,
+_tracefs_hist_sort_key_direction(3)_
+
+AUTHOR
+------
+[verse]
+--
+*Steven Rostedt* <rostedt@goodmis.org>
+*Tzvetomir Stoyanov* <tz.stoyanov@gmail.com>
+*sameeruddin shaik* <sameeruddin.shaik8@gmail.com>
+--
+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) 2020 VMware, Inc. Free use of this software is granted under
+the terms of the GNU Public License (GPL).