[PATCH 5/8] nfs: use change attribute for NFS re-exports

From: "J. Bruce Fields" <bfields@redhat.com>
To: Jeff Layton <jlayton@kernel.org>
Cc: Daire Byrne <daire@dneg.com>,
	Trond Myklebust <trondmy@hammerspace.com>,
	linux-cachefs <linux-cachefs@redhat.com>,
	linux-nfs <linux-nfs@vger.kernel.org>,
	"J. Bruce Fields" <bfields@redhat.com>
Subject: [PATCH 5/8] nfs: use change attribute for NFS re-exports
Date: Fri, 20 Nov 2020 17:39:17 -0500	[thread overview]
Message-ID: <1605911960-12516-5-git-send-email-bfields@redhat.com> (raw)
In-Reply-To: <1605911960-12516-1-git-send-email-bfields@redhat.com>

From: "J. Bruce Fields" <bfields@redhat.com>

When exporting NFS, we may as well use the real change attribute
returned by the original server instead of faking up a change attribute
from the ctime.

Note we can't do that by setting I_VERSION--that would also turn on the
logic in iversion.h which treats the lower bit specially, and that
doesn't make sense for NFS.

So instead we define a new export operation for filesystems like NFS
that want to manage the change attribute themselves.

Signed-off-by: J. Bruce Fields <bfields@redhat.com>
---
 fs/nfs/export.c          | 18 ++++++++++++++++++
 fs/nfsd/nfsfh.h          |  5 ++++-
 include/linux/exportfs.h |  1 +
 3 files changed, 23 insertions(+), 1 deletion(-)

diff --git a/fs/nfs/export.c b/fs/nfs/export.c
index 3430d6891e89..0b10c5946060 100644
--- a/fs/nfs/export.c
+++ b/fs/nfs/export.c
@@ -167,8 +167,26 @@ nfs_get_parent(struct dentry *dentry)
 	return parent;
 }
 
+static u64 nfs_fetch_iversion(struct inode *inode)
+{
+	struct nfs_server *server = NFS_SERVER(inode);
+
+	/* Is this the right call?: */
+	nfs_revalidate_inode(server, inode);
+	/*
+	 * Also, note we're ignoring any returned error.  That seems to be
+	 * the practice for cache consistency information elsewhere in
+	 * the server, but I'm not sure why.
+	 */
+	if (server->nfs_client->rpc_ops->version >= 4)
+		return inode_peek_iversion_raw(inode);
+	else
+		return time_to_chattr(&inode->i_ctime);
+}
+
 const struct export_operations nfs_export_ops = {
 	.encode_fh = nfs_encode_fh,
 	.fh_to_dentry = nfs_fh_to_dentry,
 	.get_parent = nfs_get_parent,
+	.fetch_iversion = nfs_fetch_iversion,
 };
diff --git a/fs/nfsd/nfsfh.h b/fs/nfsd/nfsfh.h
index 45bd776290d5..2656a3464c6c 100644
--- a/fs/nfsd/nfsfh.h
+++ b/fs/nfsd/nfsfh.h
@@ -12,6 +12,7 @@
 #include <linux/sunrpc/svc.h>
 #include <uapi/linux/nfsd/nfsfh.h>
 #include <linux/iversion.h>
+#include <linux/exportfs.h>
 
 static inline __u32 ino_t_to_u32(ino_t ino)
 {
@@ -259,7 +260,9 @@ fh_clear_wcc(struct svc_fh *fhp)
 static inline u64 nfsd4_change_attribute(struct kstat *stat,
 					 struct inode *inode)
 {
-	if (IS_I_VERSION(inode)) {
+	if (inode->i_sb->s_export_op->fetch_iversion)
+		return inode->i_sb->s_export_op->fetch_iversion(inode);
+	else if (IS_I_VERSION(inode)) {
 		u64 chattr;
 
 		chattr =  stat->ctime.tv_sec;
diff --git a/include/linux/exportfs.h b/include/linux/exportfs.h
index 3ceb72b67a7a..da6f0a905b94 100644
--- a/include/linux/exportfs.h
+++ b/include/linux/exportfs.h
@@ -213,6 +213,7 @@ struct export_operations {
 			  bool write, u32 *device_generation);
 	int (*commit_blocks)(struct inode *inode, struct iomap *iomaps,
 			     int nr_iomaps, struct iattr *iattr);
+	u64 (*fetch_iversion)(struct inode *);
 };
 
 extern int exportfs_encode_inode_fh(struct inode *inode, struct fid *fid,
-- 
2.28.0

