android-5.4/ANDROID-Add-a-tracepoint-for-mapping-inode-to-full-path.patch

From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Joel Fernandes <joelaf@google.com>
Date: Thu, 14 Mar 2019 17:32:39 -0400
Subject: ANDROID: Add a tracepoint for mapping inode to full path

This will be used by eBPF and the iorapd project for high speed
inode/dev numbers to file path lookup. Look at the inodemap CL for more
details about of eBPF and iorapd using the tracepoint.

This is planned to be used by the inodemap BPF program. Also, ART folks
have been using this tracepoint for debugging "unknown inode numer"
issues.

The tracepoint will be out of tree, and not sent upstream, since VFS
developers don't accept tracepoints strictly.

Test: Run "find /" command in emulator and measure completion time
with/without treacepoint. find does a flood of lookups which stresses
the tracepoint. No performance change observed.
Test: eBPF prototypes (wip) successfully read data from the tracepoint.

OOT Bug: 139663736
Bug: 135143784
Bug: 137393447
Change-Id: I657f374659673a9c8853530d73c0622dbdbab146
Signed-off-by: Joel Fernandes <joelaf@google.com>
---
 fs/namei.c                   | 90 ++++++++++++++++++++++++++++++++++--
 include/trace/events/namei.h | 42 +++++++++++++++++
 2 files changed, 129 insertions(+), 3 deletions(-)
 create mode 100644 include/trace/events/namei.h

diff --git a/fs/namei.c b/fs/namei.c
index 819aa30eea6e..c55f7019202a 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -43,6 +43,9 @@
 #include "internal.h"
 #include "mount.h"
 
+#define CREATE_TRACE_POINTS
+#include <trace/events/namei.h>
+
 /* [Feb-1997 T. Schoebel-Theuer]
  * Fundamental changes in the pathname lookup mechanisms (namei)
  * were necessary because of omirr.  The reason is that omirr needs
@@ -770,6 +773,81 @@ static inline int d_revalidate(struct dentry *dentry, unsigned int flags)
 		return 1;
 }
 
+#define INIT_PATH_SIZE 64
+
+static void success_walk_trace(struct nameidata *nd)
+{
+	struct path *pt = &nd->path;
+	struct inode *i = nd->inode;
+	char buf[INIT_PATH_SIZE], *try_buf;
+	int cur_path_size;
+	char *p;
+
+	/* When eBPF/ tracepoint is disabled, keep overhead low. */
+	if (!trace_inodepath_enabled())
+		return;
+
+	/* First try stack allocated buffer. */
+	try_buf = buf;
+	cur_path_size = INIT_PATH_SIZE;
+
+	while (cur_path_size <= PATH_MAX) {
+		/* Free previous heap allocation if we are now trying
+		 * a second or later heap allocation.
+		 */
+		if (try_buf != buf)
+			kfree(try_buf);
+
+		/* All but the first alloc are on the heap. */
+		if (cur_path_size != INIT_PATH_SIZE) {
+			try_buf = kmalloc(cur_path_size, GFP_KERNEL);
+			if (!try_buf) {
+				try_buf = buf;
+				sprintf(try_buf, "error:buf_alloc_failed");
+				break;
+			}
+		}
+
+		p = d_path(pt, try_buf, cur_path_size);
+
+		if (!IS_ERR(p)) {
+			char *end = mangle_path(try_buf, p, "\n");
+
+			if (end) {
+				try_buf[end - try_buf] = 0;
+				break;
+			} else {
+				/* On mangle errors, double path size
+				 * till PATH_MAX.
+				 */
+				cur_path_size = cur_path_size << 1;
+				continue;
+			}
+		}
+
+		if (PTR_ERR(p) == -ENAMETOOLONG) {
+			/* If d_path complains that name is too long,
+			 * then double path size till PATH_MAX.
+			 */
+			cur_path_size = cur_path_size << 1;
+			continue;
+		}
+
+		sprintf(try_buf, "error:d_path_failed_%lu",
+			-1 * PTR_ERR(p));
+		break;
+	}
+
+	if (cur_path_size > PATH_MAX)
+		sprintf(try_buf, "error:d_path_name_too_long");
+
+	trace_inodepath(i, try_buf);
+
+	if (try_buf != buf)
+		kfree(try_buf);
+	return;
+}
+
 /**
  * complete_walk - successful completion of path walk
  * @nd:  pointer nameidata
@@ -792,15 +870,21 @@ static int complete_walk(struct nameidata *nd)
 			return -ECHILD;
 	}
 
-	if (likely(!(nd->flags & LOOKUP_JUMPED)))
+	if (likely(!(nd->flags & LOOKUP_JUMPED))) {
+		success_walk_trace(nd);
 		return 0;
+	}
 
-	if (likely(!(dentry->d_flags & DCACHE_OP_WEAK_REVALIDATE)))
+	if (likely(!(dentry->d_flags & DCACHE_OP_WEAK_REVALIDATE))) {
+		success_walk_trace(nd);
 		return 0;
+	}
 
 	status = dentry->d_op->d_weak_revalidate(dentry, nd->flags);
-	if (status > 0)
+	if (status > 0) {
+		success_walk_trace(nd);
 		return 0;
+	}
 
 	if (!status)
 		status = -ESTALE;
diff --git a/include/trace/events/namei.h b/include/trace/events/namei.h
new file mode 100644
index 000000000000..e8c3e216a0a7
--- /dev/null
+++ b/include/trace/events/namei.h
@@ -0,0 +1,42 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#undef TRACE_SYSTEM
+#define TRACE_SYSTEM namei
+
+#if !defined(_TRACE_INODEPATH_H) || defined(TRACE_HEADER_MULTI_READ)
+#define _TRACE_INODEPATH_H
+
+#include <linux/types.h>
+#include <linux/tracepoint.h>
+#include <linux/mm.h>
+#include <linux/memcontrol.h>
+#include <linux/device.h>
+#include <linux/kdev_t.h>
+
+TRACE_EVENT(inodepath,
+		TP_PROTO(struct inode *inode, char *path),
+
+		TP_ARGS(inode, path),
+
+		TP_STRUCT__entry(
+			/* dev_t and ino_t are arch dependent bit width
+			 * so just use 64-bit
+			 */
+			__field(unsigned long, ino)
+			__field(unsigned long, dev)
+			__string(path, path)
+		),
+
+		TP_fast_assign(
+			__entry->ino = inode->i_ino;
+			__entry->dev = inode->i_sb->s_dev;
+			__assign_str(path, path);
+		),
+
+		TP_printk("dev %d:%d ino=%lu path=%s",
+			MAJOR(__entry->dev), MINOR(__entry->dev),
+			__entry->ino, __get_str(path))
+);
+#endif /* _TRACE_INODEPATH_H */
+
+/* This part must be outside protection */
+#include <trace/define_trace.h>