fuse_lowlevel: add tracepoints for request receiving, processing, and replying

Add user statically-defined tracepoints for request lifecycle.

Verified by:
[machine]$ readelf -n /home/libfuse/build/lib/libfuse3.so | grep -A 1000 '.note.stapsdt'
Displaying notes found in: .note.stapsdt
  Owner                Data size        Description
  stapsdt              0x00000035       NT_STAPSDT (SystemTap probe descriptors)
    Provider: libfuse
    Name: request_receive
    Location: 0x0000000000016360, Base: 0x00000000000002fc, Semaphore: 0x0000000000000000
    Arguments: -4@%edi
  stapsdt              0x00000055       NT_STAPSDT (SystemTap probe descriptors)
    Provider: libfuse
    Name: request_reply
    Location: 0x0000000000017c0f, Base: 0x00000000000002fc, Semaphore: 0x0000000000000000
    Arguments: 8@8(%r12) 4@(%r12) -4@4(%r12) -4@%r13d
  stapsdt              0x0000003e       NT_STAPSDT (SystemTap probe descriptors)
    Provider: libfuse
    Name: request_process
    Location: 0x000000000001acf7, Base: 0x00000000000002fc, Semaphore: 0x0000000000000000
    Arguments: 4@%r8d 4@%edx

Signed-off-by: Joanne Koong <joannelkoong@gmail.com>

1 files changed, 23 insertions, 0 deletions

diff --git a/lib/fuse_lowlevel.c b/lib/fuse_lowlevel.c
index 17bc816..a5d9e0c 100644
--- a/lib/fuse_lowlevel.c
+++ b/lib/fuse_lowlevel.c
@@ -17,6 +17,7 @@
 #include "fuse_opt.h"
 #include "fuse_misc.h"
 #include "mount_util.h"
+#include "usdt.h"
 #include "util.h"
 
 #include <stdint.h>
@@ -60,6 +61,23 @@ static __attribute__((constructor)) void fuse_ll_init_pagesize(void)
 	pagesize = getpagesize();
 }
 
+/* tracepoints */
+static void trace_request_receive(int err)
+{
+	USDT(libfuse, request_receive, err);
+}
+
+static void trace_request_process(unsigned int opcode, unsigned int unique)
+{
+	USDT(libfuse, request_process, opcode, unique);
+}
+
+static void trace_request_reply(uint64_t unique, unsigned int len,
+				int error, int reply_err)
+{
+	USDT(libfuse, request_reply, unique, len, error, reply_err);
+}
+
 static void convert_stat(const struct stat *stbuf, struct fuse_attr *attr)
 {
 	attr->ino	= stbuf->st_ino;
@@ -207,6 +225,7 @@ static int fuse_send_msg(struct fuse_session *se, struct fuse_chan *ch,
 		res = writev(ch ? ch->fd : se->fd, iov, count);
 
 	int err = errno;
+	trace_request_reply(out->unique, out->len, out->error, err);
 
 	if (res == -1) {
 		/* ENOENT means the operation was interrupted */
@@ -2809,6 +2828,8 @@ void fuse_session_process_buf_internal(struct fuse_session *se,
 		in = buf->mem;
 	}
 
+	trace_request_process(in->opcode, in->unique);
+
 	if (se->debug) {
 		fuse_log(FUSE_LOG_DEBUG,
 			"unique: %llu, opcode: %s (%i), nodeid: %llu, insize: %zu, pid: %u\n",
@@ -3067,6 +3088,7 @@ pipe_retry:
 			     bufsize, 0);
 	}
 	err = errno;
+	trace_request_receive(err);
 
 	if (fuse_session_exited(se))
 		return 0;
@@ -3171,6 +3193,7 @@ restart:
 		res = read(ch ? ch->fd : se->fd, buf->mem, bufsize);
 	}
 	err = errno;
+	trace_request_receive(err);
 
 	if (fuse_session_exited(se))
 		return 0;