NFS: Add offset to nfs_aop_readahead tracepoint

Add the byte offset of the readahead request to the tracepoint output
so we know where the read starts.

Before this patch:
cat-8104    [002] .....   813.168775: nfs_aop_readahead: fileid=00:31:141 fhandle=0xe55807f6 version=1756509392533525500 nr_pages=256
cat-8104    [002] .....   813.174973: nfs_aop_readahead_done: fileid=00:31:141 fhandle=0xe55807f6 version=1756509392533525500 nr_pages=256 ret=0
cat-8104    [002] .....   813.175963: nfs_aop_readahead: fileid=00:31:141 fhandle=0xe55807f6 version=1756509392533525500 nr_pages=256
cat-8104    [002] .....   813.183742: nfs_aop_readahead_done: fileid=00:31:141 fhandle=0xe55807f6 version=1756509392533525500 nr_pages=1 ret=0

After this patch:
cat-6392    [001] .....    73.107782: nfs_aop_readahead: fileid=00:31:141 fhandle=0xed22403f version=1756511950029502774 offset=5242880 nr_pages=256
cat-6392    [001] .....    73.112466: nfs_aop_readahead_done: fileid=00:31:141 fhandle=0xed22403f version=1756511950029502774 nr_pages=256 ret=0
cat-6392    [001] .....    73.115692: nfs_aop_readahead: fileid=00:31:141 fhandle=0xed22403f version=1756511950029502774 offset=6291456 nr_pages=256
cat-6392    [001] .....    73.123283: nfs_aop_readahead_done: fileid=00:31:141 fhandle=0xed22403f version=1756511950029502774 nr_pages=256 ret=0
Signed-off-by: Dave Wysochanski <dwysocha@redhat.com>
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>

fs/nfs/nfstrace.h

@@ -889,16 +889,18 @@ TRACE_EVENT(nfs_aop_readpage_done,
 TRACE_EVENT(nfs_aop_readahead,
 		TP_PROTO(
 			const struct inode *inode,
+			struct page *page,
 			unsigned int nr_pages
 		),
 
-		TP_ARGS(inode, nr_pages),
+		TP_ARGS(inode, page, nr_pages),
 
 		TP_STRUCT__entry(
 			__field(dev_t, dev)
 			__field(u32, fhandle)
 			__field(u64, fileid)
 			__field(u64, version)
+			__field(loff_t, offset)
 			__field(unsigned int, nr_pages)
 		),
 
@@ -909,15 +911,16 @@ TRACE_EVENT(nfs_aop_readahead,
 			__entry->fileid = nfsi->fileid;
 			__entry->fhandle = nfs_fhandle_hash(&nfsi->fh);
 			__entry->version = inode_peek_iversion_raw(inode);
+			__entry->offset = page_index(page) << PAGE_SHIFT;
 			__entry->nr_pages = nr_pages;
 		),
 
 		TP_printk(
-			"fileid=%02x:%02x:%llu fhandle=0x%08x version=%llu nr_pages=%u",
+			"fileid=%02x:%02x:%llu fhandle=0x%08x version=%llu offset=%lld nr_pages=%u",
 			MAJOR(__entry->dev), MINOR(__entry->dev),
 			(unsigned long long)__entry->fileid,
 			__entry->fhandle, __entry->version,
-			__entry->nr_pages
+			__entry->offset, __entry->nr_pages
 		)
 );
 
@@ -936,6 +939,7 @@ TRACE_EVENT(nfs_aop_readahead_done,
 			__field(int, ret)
 			__field(u64, fileid)
 			__field(u64, version)
+			__field(loff_t, offset)
 			__field(unsigned int, nr_pages)
 		),
 

fs/nfs/read.c

@@ -404,7 +404,7 @@ int nfs_readpages(struct file *file, struct address_space *mapping,
 	struct inode *inode = mapping->host;
 	int ret;
 
-	trace_nfs_aop_readahead(inode, nr_pages);
+	trace_nfs_aop_readahead(inode, lru_to_page(pages), nr_pages);
 	nfs_inc_stats(inode, NFSIOS_VFSREADPAGES);
 
 	ret = -ESTALE;