This patch allows passing perf's own PID to '--filter' by using
'@PERFPID'. This should be useful when system-widely capturing
tracepoints events.

Before this patch, when doing something like:

 # perf record -a -e syscalls:sys_enter_write <cmd>

One could easily get result like this:

 # /tmp/perf report --stdio
 ...
 # Overhead  Command  Shared Object       Symbol
 # ........  .......  ..................  ....................
 #
     99.99%  perf     libpthread-2.18.so  [.] __write_nocancel
     0.01%   ls       libc-2.18.so        [.] write
     0.01%   sshd     libc-2.18.so        [.] write
     ...

Where most events are generated by perf itself.

A shell trick can be done to filter perf itself out:

 # cat << EOF > ./tmp
 > #!/bin/sh
 > exec perf record -e ... --filter="common_pid != \$\$" -a sleep 10
 > EOF
 # chmod a+x ./tmp
 # ./tmp

However, doing so is user unfriendly.

This patch introduces '@PERFPID' placeholder to '--filter' options. Now
user is allowed to the above work with:

  # perf record -e ... --filter="common_pid != @PERFPID' sleep 10

Signed-off-by: Wang Nan <wangn...@huawei.com>
---
 tools/perf/Documentation/perf-record.txt |  1 +
 tools/perf/util/parse-events.c           | 96 ++++++++++++++++++++++++++++++++
 2 files changed, 97 insertions(+)

diff --git a/tools/perf/Documentation/perf-record.txt 
b/tools/perf/Documentation/perf-record.txt
index 9b9d9d0..c2902d2 100644
--- a/tools/perf/Documentation/perf-record.txt
+++ b/tools/perf/Documentation/perf-record.txt
@@ -62,6 +62,7 @@ OPTIONS
 
 --filter=<filter>::
         Event filter.
+        String '@PERFPID' is allowed to be used to represent pid of 'perf' 
itself.
 
 -a::
 --all-cpus::
diff --git a/tools/perf/util/parse-events.c b/tools/perf/util/parse-events.c
index aaee24c..2d62957 100644
--- a/tools/perf/util/parse-events.c
+++ b/tools/perf/util/parse-events.c
@@ -1175,6 +1175,101 @@ int parse_events_option(const struct option *opt, const 
char *str,
        return ret;
 }
 
+#ifndef PAGE_SIZE
+# define PAGE_SIZE 4096
+#endif
+static int
+postproc_filter_append_token(const char *key, char *new_filter,
+                            ssize_t *pspace)
+{
+       if (strcmp(key, "PERFPID") == 0) {
+               char pid_buf[32];
+               pid_t self_pid = getpid();
+
+               snprintf(pid_buf, 32, "%d", self_pid);
+               strncat(new_filter, pid_buf, *pspace);
+               *pspace -= strlen(pid_buf);
+               if (*pspace < 0)
+                       return -1;
+               return 0;
+       }
+
+       return -1;
+}
+
+static void postproc_filter(struct perf_evsel *evsel)
+{
+       char *at = NULL, *sep = NULL, *old_filter, *new_filter;
+       ssize_t space;
+
+       if (!evsel->filter)
+               return;
+
+       old_filter = evsel->filter;
+       at = strchr(old_filter, '@');
+       if (!at)
+               return;
+
+       /*
+        * See perf_event_set_filter(). Length of a valid filter is
+        * limited by PAGE_SIZE.
+        */
+       new_filter = malloc(PAGE_SIZE);
+       if (!new_filter) {
+               fprintf(stderr, "No enough memory for post proc filter '%s'\n",
+                       old_filter);
+               return;
+       }
+       *new_filter = '\0';
+       space = PAGE_SIZE - 1;
+
+       while (1) {
+               if (at)
+                       *at = '\0';
+               strncat(new_filter, old_filter, space);
+               space -= strlen(old_filter);
+               if (space < 0)
+                       goto errout;
+               if (!at)
+                       break;
+               *at = '@';
+
+               sep = strchr(at + 1, ' ');
+               if (sep)
+                       *sep = '\0';
+
+               if (postproc_filter_append_token(at + 1, new_filter, &space))
+                       goto errout;
+
+               if (!sep)
+                       break;
+               *sep = ' ';
+
+               old_filter = sep;
+               at = strchr(old_filter, '@');
+       }
+
+       free(evsel->filter);
+       /*
+        * It is safe to use new_filter directly. However, try to
+        * release some memory by strdup() a smaller string and free
+        * new_filter, which takes a full page.
+        */
+       evsel->filter = strdup(new_filter);
+       if (!evsel->filter)
+               evsel->filter = new_filter;
+       else
+               free(new_filter);
+       return;
+errout:
+       if (at)
+               *at = '@';
+       if (sep)
+               *sep = ' ';
+       fprintf(stderr, "Can't post proc filter '%s'\n", evsel->filter);
+       free(new_filter);
+}
+
 int parse_filter(const struct option *opt, const char *str,
                 int unset __maybe_unused)
 {
@@ -1196,6 +1291,7 @@ int parse_filter(const struct option *opt, const char 
*str,
                return -1;
        }
 
+       postproc_filter(last);
        return 0;
 }
 
-- 
1.8.3.4

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