[PATCH 1/3] nfs: use change attribute for NFS re-exports

J. Bruce Fields
2021-01-19T19:41:25Z

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 7412bb164fa7..f2b34cfe286c 100644
--- a/fs/nfs/export.c
+++ b/fs/nfs/export.c
@@ -167,10 +167,28 @@ 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,
.flags = EXPORT_OP_NOWCC|EXPORT_OP_NOSUBTREECHK|
EXPORT_OP_CLOSE_BEFORE_UNLINK|EXPORT_OP_REMOTE_FS|
EXPORT_OP_NOATOMIC_ATTR,
diff --git a/fs/nfsd/nfsfh.h b/fs/nfsd/nfsfh.h
index cb20c2cd3469..f58933519f38 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)
{
@@ -264,7 +265,9 @@ 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 9f4d4bcbf251..fe848901fcc3 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 *);
#define EXPORT_OP_NOWCC (0x1) /* don't collect v3 wcc data */
#define EXPORT_OP_NOSUBTREECHK (0x2) /* no subtree checking */
#define EXPORT_OP_CLOSE_BEFORE_UNLINK (0x4) /* close files before unlink */
--
2.29.2