[PATCH v3] Add 4 tracepoint events for vfs

[chenggang.qin@gmail.com]

From: chenggang.qin@gmail.com

This version changed some type definition according to Steven's advise.
Thanks for Steven.

If the engineers want to analyze the file access behavior of some applications without source code, perf tools with some appropriate tracepoints events in the VFS subsystem are excellent choice.

The system engineers or developers of server software require to know what files are accessed by the target processes with in a period of time. Then they can find the hot applications and the hot files. For this requirements, we added 2 tracepoint events at the begin of generic_file_aio_read() and generic_file_aio_write().

Many database systems use their own page cache subsystems and use the direct IO to access the disks. Sometimes, the system engineers want to know the misses rate of the database system's page cache. This requirements can be satisfied by recording the database's file access behavior through the way of direct IO. So, we added 2 tracepoint events at the direct IO branch in generic_file_aio_read() and generic_file_aio_write().

Then, we will extend the perf's function by python script to use these new tracepoint events.

The 4 new tracepoint events are:
1) generic_file_aio_read
   Format:
	field:unsigned short common_type;	offset:0;	size:2;	signed:0;
	field:unsigned char common_flags;	offset:2;	size:1;	signed:0;
	field:unsigned char common_preempt_count;	offset:3;	size:1;	signed:0;
	field:int common_pid;	offset:4;	size:4;	signed:1;
	field:int common_padding;	offset:8;	size:4;	signed:1;

	field:long long pos;	offset:16;	size:8;	signed:1;
	field:unsigned long bytes;	offset:24;	size:8;	signed:0;
	field:__data_loc char[] fname;	offset:32;	size:4;	signed:1;

2) generic_file_aio_write
   Format:
	field:unsigned short common_type;	offset:0;	size:2;	signed:0;
	field:unsigned char common_flags;	offset:2;	size:1;	signed:0;
	field:unsigned char common_preempt_count;	offset:3;	size:1;	signed:0;
	field:int common_pid;	offset:4;	size:4;	signed:1;
	field:int common_padding;	offset:8;	size:4;	signed:1;

	field:long long pos;	offset:16;	size:8;	signed:1;
	field:unsigned long bytes;	offset:24;	size:8;	signed:0;
	field:__data_loc char[] fname;	offset:32;	size:4;	signed:1;

3) direct_io_read
   Format:
	field:unsigned short common_type;	offset:0;	size:2;	signed:0;
	field:unsigned char common_flags;	offset:2;	size:1;	signed:0;
	field:unsigned char common_preempt_count;	offset:3;	size:1;	signed:0;
	field:int common_pid;	offset:4;	size:4;	signed:1;
	field:int common_padding;	offset:8;	size:4;	signed:1;

	field:long long pos;	offset:16;	size:8;	signed:1;
	field:unsigned long bytes;	offset:24;	size:8;	signed:0;
	field:unsigned char fname[100];	offset:32;	size:100;	signed:0;

4) direct_io_write
   Format:
	field:unsigned short common_type;	offset:0;	size:2;	signed:0;
	field:unsigned char common_flags;	offset:2;	size:1;	signed:0;
	field:unsigned char common_preempt_count;	offset:3;	size:1;	signed:0;
	field:int common_pid;	offset:4;	size:4;	signed:1;
	field:int common_padding;	offset:8;	size:4;	signed:1;

	field:long long pos;	offset:16;	size:8;	signed:1;
	field:unsigned long bytes;	offset:24;	size:8;	signed:0;
	field:unsigned char fname[100];	offset:32;	size:100;	signed:0;

Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Cc: Namhyung Kim <namhyung@gmail.com>
Cc: Yanmin Zhang <yanmin.zhang@intel.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Chenggang Qin <chenggang.qcg@alibaba-inc.com>

---
 include/trace/events/vfs.h |   62 ++++++++++++++++++++++++++++++++++++++++++++
 mm/filemap.c               |   18 +++++++++++++
 2 files changed, 80 insertions(+)
 create mode 100644 include/trace/events/vfs.h

diff --git a/include/trace/events/vfs.h b/include/trace/events/vfs.h
new file mode 100644
index 0000000..11c9acc
--- /dev/null
+++ b/include/trace/events/vfs.h
@@ -0,0 +1,62 @@
+#undef TRACE_SYSTEM
+#define TRACE_SYSTEM vfs
+#define TRACE_INCLUDE_FILE vfs
+
+#if !defined(_TRACE_EVENTS_VFS_H) || defined(TRACE_HEADER_MULTI_READ)
+#define _TRACE_EVENTS_VFS_H
+
+#include <linux/tracepoint.h>
+
+#include <asm/ptrace.h>
+
+DECLARE_EVENT_CLASS(vfs_filerw_template,
+
+	TP_PROTO(long long pos, unsigned long bytes, const unsigned char *fname),
+
+	TP_ARGS(pos, bytes, fname),
+
+        TP_STRUCT__entry(
+		__field(        long long,      pos             )
+		__field(        unsigned long,  bytes           )
+		__string(       fname,          fname           )
+	),
+
+	TP_fast_assign(
+		__entry->pos    = pos;
+		__entry->bytes  = bytes;
+		__assign_str(fname, fname);
+	),
+
+	TP_printk("Filename: %s Pos: %lld Bytes: %lu",
+		  __get_str(fname), __entry->pos, __entry->bytes)
+);
+
+DEFINE_EVENT(vfs_filerw_template, generic_file_aio_read,
+	     TP_PROTO(long long pos, unsigned long bytes, const unsigned char *fname),
+	     TP_ARGS(pos, bytes, fname));
+
+TRACE_EVENT_FLAGS(generic_file_aio_read, TRACE_EVENT_FL_CAP_ANY)
+
+DEFINE_EVENT(vfs_filerw_template, generic_file_aio_write,
+	     TP_PROTO(long long pos, unsigned long bytes, const unsigned char *fname),
+	     TP_ARGS(pos, bytes, fname));
+
+TRACE_EVENT_FLAGS(generic_file_aio_write, TRACE_EVENT_FL_CAP_ANY)
+
+DEFINE_EVENT(vfs_filerw_template, direct_io_read,
+	     TP_PROTO(long long pos, unsigned long bytes, const unsigned char *fname),
+	     TP_ARGS(pos, bytes, fname));
+
+TRACE_EVENT_FLAGS(direct_io_read, TRACE_EVENT_FL_CAP_ANY)
+
+DEFINE_EVENT(vfs_filerw_template, direct_io_write,
+	     TP_PROTO(long long pos, unsigned long bytes, const unsigned char *fname),
+	     TP_ARGS(pos, bytes, fname));
+
+TRACE_EVENT_FLAGS(direct_io_write, TRACE_EVENT_FL_CAP_ANY)
+
+#endif /* _TRACE_EVENTS_VFS_H */
+
+/* This part must be outside protection */
+#include <trace/define_trace.h>
+
diff --git a/mm/filemap.c b/mm/filemap.c
index 83efee7..dc587e7 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -42,6 +42,9 @@
 
 #include <asm/mman.h>
 
+#define CREATE_TRACE_POINTS
+#include <trace/events/vfs.h>
+
 /*
  * Shared mappings implemented 30.11.1994. It's not fully working yet,
  * though.
@@ -1391,12 +1394,16 @@ generic_file_aio_read(struct kiocb *iocb, const struct iovec *iov,
 	unsigned long seg = 0;
 	size_t count;
 	loff_t *ppos = &iocb->ki_pos;
+	const unsigned char *f_name;
 
 	count = 0;
 	retval = generic_segment_checks(iov, &nr_segs, &count, VERIFY_WRITE);
 	if (retval)
 		return retval;
 
+	f_name = filp->f_path.dentry->d_name.name;
+	trace_generic_file_aio_read(pos, iov_length(iov, nr_segs), f_name);
+
 	/* coalesce the iovecs and go direct-to-BIO for O_DIRECT */
 	if (filp->f_flags & O_DIRECT) {
 		loff_t size;
@@ -1407,6 +1414,9 @@ generic_file_aio_read(struct kiocb *iocb, const struct iovec *iov,
 		inode = mapping->host;
 		if (!count)
 			goto out; /* skip atime */
+
+		trace_direct_io_read(pos, iov_length(iov, nr_segs), f_name);
+
 		size = i_size_read(inode);
 		if (pos < size) {
 			retval = filemap_write_and_wait_range(mapping, pos,
@@ -2453,6 +2463,10 @@ ssize_t __generic_file_aio_write(struct kiocb *iocb, const struct iovec *iov,
 	if (unlikely(file->f_flags & O_DIRECT)) {
 		loff_t endbyte;
 		ssize_t written_buffered;
+		const unsigned char *f_name;
+
+		f_name = file->f_path.dentry->d_name.name;
+		trace_direct_io_write(pos, iov_length(iov, nr_segs), f_name);
 
 		written = generic_file_direct_write(iocb, iov, &nr_segs, pos,
 							ppos, count, ocount);
@@ -2524,9 +2538,13 @@ ssize_t generic_file_aio_write(struct kiocb *iocb, const struct iovec *iov,
 	struct file *file = iocb->ki_filp;
 	struct inode *inode = file->f_mapping->host;
 	ssize_t ret;
+	const unsigned char *f_name;
 
 	BUG_ON(iocb->ki_pos != pos);
 
+	f_name = file->f_path.dentry->d_name.name;
+	trace_generic_file_aio_write(pos, iov_length(iov, nr_segs), f_name);
+
 	sb_start_write(inode->i_sb);
 	mutex_lock(&inode->i_mutex);
 	ret = __generic_file_aio_write(iocb, iov, nr_segs, &iocb->ki_pos);
-- 
1.7.9.5