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Subject[PATCH 8/8] trace_uprobe/sdt: Document about reference counter
Date
No functionality changes.

Signed-off-by: Ravi Bangoria <ravi.bangoria@linux.vnet.ibm.com>
---
Documentation/trace/uprobetracer.txt | 16 +++++++++++++---
kernel/trace/trace.c | 2 +-
2 files changed, 14 insertions(+), 4 deletions(-)

diff --git a/Documentation/trace/uprobetracer.txt b/Documentation/trace/uprobetracer.txt
index bf526a7c..8fb13b0 100644
--- a/Documentation/trace/uprobetracer.txt
+++ b/Documentation/trace/uprobetracer.txt
@@ -19,15 +19,25 @@ user to calculate the offset of the probepoint in the object.

Synopsis of uprobe_tracer
-------------------------
- p[:[GRP/]EVENT] PATH:OFFSET [FETCHARGS] : Set a uprobe
- r[:[GRP/]EVENT] PATH:OFFSET [FETCHARGS] : Set a return uprobe (uretprobe)
- -:[GRP/]EVENT : Clear uprobe or uretprobe event
+ p[:[GRP/]EVENT] PATH:OFFSET[(REF_CTR_OFFSET)] [FETCHARGS]
+ r[:[GRP/]EVENT] PATH:OFFSET[(REF_CTR_OFFSET)] [FETCHARGS]
+ -:[GRP/]EVENT
+
+ p : Set a uprobe
+ r : Set a return uprobe (uretprobe)
+ - : Clear uprobe or uretprobe event

GRP : Group name. If omitted, "uprobes" is the default value.
EVENT : Event name. If omitted, the event name is generated based
on PATH+OFFSET.
PATH : Path to an executable or a library.
OFFSET : Offset where the probe is inserted.
+ REF_CTR_OFFSET: Reference counter offset. Optional field. Reference count
+ gate the invocation of probe. If present, by default
+ reference count is 0. Kernel needs to increment it before
+ tracing the probe and decrement it when done. This is
+ identical to semaphore in Userspace Statically Defined
+ Tracepoints (USDT).

FETCHARGS : Arguments. Each probe can have up to 128 args.
%REG : Fetch register REG
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 20a2300..2104d03 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -4604,7 +4604,7 @@ static int tracing_trace_options_open(struct inode *inode, struct file *file)
"place (kretprobe): [<module>:]<symbol>[+<offset>]|<memaddr>\n"
#endif
#ifdef CONFIG_UPROBE_EVENTS
- "\t place: <path>:<offset>\n"
+ " place (uprobe): <path>:<offset>[(ref_ctr_offset)]\n"
#endif
"\t args: <name>=fetcharg[:type]\n"
"\t fetcharg: %<register>, @<address>, @<symbol>[+|-<offset>],\n"
--
1.8.3.1
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