Linux 3.16 (more specifically, commit 82b897782d10fcc4 )
added support for differentiating between process renames
caused by exec versus those caused by other methods.
Signed-off-by: Vince Weaver <vincent.weaver@xxxxxxxxx>
diff --git a/man2/perf_event_open.2 b/man2/perf_event_open.2
index d558379..cb15428 100644
--- a/man2/perf_event_open.2
+++ b/man2/perf_event_open.2
@@ -226,7 +226,8 @@ struct perf_event_attr {
exclude_callchain_user : 1,
/* exclude user callchains */
mmap2 : 1, /* include mmap with inode data */
- __reserved_1 : 40;
+ comm_exec : 1, /* flag comm events that are due to exec */
+ __reserved_1 : 39;
union {
__u32 wakeup_events; /* wakeup every n events */
@@ -861,9 +862,16 @@ bit enables tracking of process command name as modified by the
.BR exec (2)
and
.BR prctl (PR_SET_NAME)
-system calls.
-Unfortunately for tools,
-there is no way to distinguish one system call versus the other.
+system calls as well as writing to
+.IR /proc/self/comm .
+If the additional
+.I comm_exec
+flag can be set (starting with Linux 3.16)
+then the misc flag
+.B PERF_RECORD_MISC_COMM_EXEC
+can be used to differentiate the
+.BR exec (2)
+case from the others.
.TP
.IR "freq"
If this bit is set, then
@@ -988,6 +996,21 @@ The
.I mmap
flag must also be set for this to work.
.TP
+.IR "comm_exec" " (since Linux 3.16)"
+This is purely a feature detection flag, it does not change
+kernel behavior.
+If this flag can successfully be set, then when
+.I comm
+is enabled a
+.B PERF_RECORD_MISC_COMM_EXEC
+flag will be set in the
+.I misc
+field of a comm record header if the rename event being
+reported was caused by a call to
+.BR exec (2).
+This allows tools to distinguish between the various
+types of process renaming.
+.TP
.IR "wakeup_events" ", " "wakeup_watermark"
This union sets how many samples
.RI ( wakeup_events )
@@ -1550,6 +1573,17 @@ In addition, one of the following bits can be set:
This is set when the mapping is not executable;
otherwise the mapping is executable.
.TP
+.B PERF_RECORD_MISC_COMM_EXEC
+This is set for a
+.B PERF_RECORD_COMM
+record on kernels more recent than Linux 3.16
+if a process name change was caused by an
+.BR exec (2)
+system call.
+It is an alias for
+.B PERF_RECORD_MISC_MMAP_DATA
+since the two values would not be set in the same record.
+.TP
.B PERF_RECORD_MISC_EXACT_IP
This indicates that the content of
.B PERF_SAMPLE_IP
@@ -1645,6 +1679,17 @@ struct {
};
.fi
.in
+.RS
+.TP
+.I pid
+is the process id.
+.TP
+.I tid
+is the thread id.
+.TP
+.I comm
+is a string containing the new name of the process.
+.RE
.TP
.B PERF_RECORD_EXIT
This record indicates a process exit event.
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