1 files changed, 46 insertions, 0 deletions
diff --git a/fs/libfs.c b/fs/libfs.c
index 31b0ddf01c31..682d56345a1c 100644
--- a/fs/libfs.c
+++ b/fs/libfs.c
@@ -15,6 +15,7 @@
 #include <linux/mutex.h>
 #include <linux/namei.h>
 #include <linux/exportfs.h>
+#include <linux/iversion.h>
 #include <linux/writeback.h>
 #include <linux/buffer_head.h> /* sync_mapping_buffers */
 #include <linux/fs_context.h>
@@ -1520,3 +1521,48 @@ void generic_set_encrypted_ci_d_ops(struct dentry *dentry)
 #endif
 }
 EXPORT_SYMBOL(generic_set_encrypted_ci_d_ops);
+
+/**
+ * inode_maybe_inc_iversion - increments i_version
+ * @inode: inode with the i_version that should be updated
+ * @force: increment the counter even if it's not necessary?
+ *
+ * Every time the inode is modified, the i_version field must be seen to have
+ * changed by any observer.
+ *
+ * If "force" is set or the QUERIED flag is set, then ensure that we increment
+ * the value, and clear the queried flag.
+ *
+ * In the common case where neither is set, then we can return "false" without
+ * updating i_version.
+ *
+ * If this function returns false, and no other metadata has changed, then we
+ * can avoid logging the metadata.
+ */
+bool inode_maybe_inc_iversion(struct inode *inode, bool force)
+{
+	u64 cur, new;
+
+	/*
+	 * The i_version field is not strictly ordered with any other inode
+	 * information, but the legacy inode_inc_iversion code used a spinlock
+	 * to serialize increments.
+	 *
+	 * Here, we add full memory barriers to ensure that any de-facto
+	 * ordering with other info is preserved.
+	 *
+	 * This barrier pairs with the barrier in inode_query_iversion()
+	 */
+	smp_mb();
+	cur = inode_peek_iversion_raw(inode);
+	do {
+		/* If flag is clear then we needn't do anything */
+		if (!force && !(cur & I_VERSION_QUERIED))
+			return false;
+
+		/* Since lowest bit is flag, add 2 to avoid it */
+		new = (cur & ~I_VERSION_QUERIED) + I_VERSION_INCREMENT;
+	} while (!atomic64_try_cmpxchg(&inode->i_version, &cur, new));
+	return true;
+}
+EXPORT_SYMBOL(inode_maybe_inc_iversion);