linux-kernel - [PATCH 23/67] cachefiles: trace: Improve the lookup tracepoint

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Date:   Mon, 18 Oct 2021 15:56:45 +0100
From:   David Howells <dhowells@...hat.com>
To:     linux-cachefs@...hat.com
Cc:     dhowells@...hat.com, Trond Myklebust <trondmy@...merspace.com>,
        Anna Schumaker <anna.schumaker@...app.com>,
        Steve French <sfrench@...ba.org>,
        Dominique Martinet <asmadeus@...ewreck.org>,
        Jeff Layton <jlayton@...hat.com>,
        Matthew Wilcox <willy@...radead.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Omar Sandoval <osandov@...ndov.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-afs@...ts.infradead.org, linux-nfs@...r.kernel.org,
        linux-cifs@...r.kernel.org, ceph-devel@...r.kernel.org,
        v9fs-developer@...ts.sourceforge.net,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH 23/67] cachefiles: trace: Improve the lookup tracepoint

Improve the cachefiles_lookup tracepoint:

 - Don't display the dentry address, since it's going to get hashed.

 - Do display any error code.

 - Work out the inode in the tracepoint rather than in the caller so that
   the logic is conditional on the tracepoint being enabled.

Signed-off-by: David Howells <dhowells@...hat.com>
---

 fs/cachefiles/namei.c             |    4 +---
 include/trace/events/cachefiles.h |   18 +++++++++---------
 2 files changed, 10 insertions(+), 12 deletions(-)

diff --git a/fs/cachefiles/namei.c b/fs/cachefiles/namei.c
index 10b6d571eda8..b5a0aec529af 100644
--- a/fs/cachefiles/namei.c
+++ b/fs/cachefiles/namei.c
@@ -340,14 +340,12 @@ static int cachefiles_walk_to_file(struct cachefiles_cache *cache,
 	inode_lock_nested(dinode, I_MUTEX_PARENT);
 
 	dentry = lookup_one_len(object->d_name, fan, object->d_name_len);
+	trace_cachefiles_lookup(object, dentry);
 	if (IS_ERR(dentry)) {
-		trace_cachefiles_lookup(object, dentry, NULL);
 		ret = PTR_ERR(dentry);
 		goto error;
 	}
 
-	trace_cachefiles_lookup(object, dentry, d_backing_inode(dentry));
-
 	if (d_is_negative(dentry)) {
 		/* This element of the path doesn't exist, so we can release
 		 * any readers in the certain knowledge that there's nothing
diff --git a/include/trace/events/cachefiles.h b/include/trace/events/cachefiles.h
index bd0b5bbd3889..87681dd957ec 100644
--- a/include/trace/events/cachefiles.h
+++ b/include/trace/events/cachefiles.h
@@ -98,25 +98,25 @@ TRACE_EVENT(cachefiles_ref,
 
 TRACE_EVENT(cachefiles_lookup,
 	    TP_PROTO(struct cachefiles_object *obj,
-		     struct dentry *de,
-		     struct inode *inode),
+		     struct dentry *de),
 
-	    TP_ARGS(obj, de, inode),
+	    TP_ARGS(obj, de),
 
 	    TP_STRUCT__entry(
 		    __field(unsigned int,		obj	)
-		    __field(struct dentry *,		de	)
-		    __field(struct inode *,		inode	)
+		    __field(short,			error	)
+		    __field(unsigned long,		ino	)
 			     ),
 
 	    TP_fast_assign(
 		    __entry->obj	= obj->fscache.debug_id;
-		    __entry->de		= de;
-		    __entry->inode	= inode;
+		    __entry->ino	= (!IS_ERR(de) && d_backing_inode(de) ?
+					   d_backing_inode(de)->i_ino : 0);
+		    __entry->error	= IS_ERR(de) ? PTR_ERR(de) : 0;
 			   ),
 
-	    TP_printk("o=%08x d=%p i=%p",
-		      __entry->obj, __entry->de, __entry->inode)
+	    TP_printk("o=%08x i=%lx e=%d",
+		      __entry->obj, __entry->ino, __entry->error)
 	    );
 
 TRACE_EVENT(cachefiles_create,