Merge tag 'iversion-v6.3' of git://git.kernel.org/pub/scm/linux/kernel/git/jlayton/linux

Pull i_version updates from Jeff Layton:
 "This overhauls how we handle i_version queries from nfsd.

  Instead of having special routines and grabbing the i_version field
  directly out of the inode in some cases, we've moved most of the
  handling into the various filesystems' getattr operations. As a bonus,
  this makes ceph's change attribute usable by knfsd as well.

  This should pave the way for future work to make this value queryable
  by userland, and to make it more resilient against rolling back on a
  crash"

* tag 'iversion-v6.3' of git://git.kernel.org/pub/scm/linux/kernel/git/jlayton/linux:
  nfsd: remove fetch_iversion export operation
  nfsd: use the getattr operation to fetch i_version
  nfsd: move nfsd4_change_attribute to nfsfh.c
  ceph: report the inode version in getattr if requested
  nfs: report the inode version in getattr if requested
  vfs: plumb i_version handling into struct kstat
  fs: clarify when the i_version counter must be updated
  fs: uninline inode_query_iversion

1 files changed, 36 insertions, 0 deletions

diff --git a/fs/libfs.c b/fs/libfs.c
index aada4e7c8713..17ecc47696e1 100644
--- a/fs/libfs.c
+++ b/fs/libfs.c
@@ -1582,3 +1582,39 @@ bool inode_maybe_inc_iversion(struct inode *inode, bool force)
 	return true;
 }
 EXPORT_SYMBOL(inode_maybe_inc_iversion);
+
+/**
+ * inode_query_iversion - read i_version for later use
+ * @inode: inode from which i_version should be read
+ *
+ * Read the inode i_version counter. This should be used by callers that wish
+ * to store the returned i_version for later comparison. This will guarantee
+ * that a later query of the i_version will result in a different value if
+ * anything has changed.
+ *
+ * In this implementation, we fetch the current value, set the QUERIED flag and
+ * then try to swap it into place with a cmpxchg, if it wasn't already set. If
+ * that fails, we try again with the newly fetched value from the cmpxchg.
+ */
+u64 inode_query_iversion(struct inode *inode)
+{
+	u64 cur, new;
+
+	cur = inode_peek_iversion_raw(inode);
+	do {
+		/* If flag is already set, then no need to swap */
+		if (cur & I_VERSION_QUERIED) {
+			/*
+			 * This barrier (and the implicit barrier in the
+			 * cmpxchg below) pairs with the barrier in
+			 * inode_maybe_inc_iversion().
+			 */
+			smp_mb();
+			break;
+		}
+
+		new = cur | I_VERSION_QUERIED;
+	} while (!atomic64_try_cmpxchg(&inode->i_version, &cur, new));
+	return cur >> I_VERSION_QUERIED_SHIFT;
+}
+EXPORT_SYMBOL(inode_query_iversion);