[13/16] iversion: add a routine to update a raw value with a larger one

Commit Message

Jeff Layton June 7, 2019, 3:38 p.m. UTC

Machines can be independently updating iversion themselves, while
working under comprehensive sets of caps on an inode. Add a new
function that will update a raw value with a larger one.

Signed-off-by: Jeff Layton <[e-mail]>
---
 include/linux/iversion.h | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

Patch

diff --git a/include/linux/iversion.h b/include/linux/iversion.h
index be50ef7cedab..2917ef990d43 100644
--- a/include/linux/iversion.h
+++ b/include/linux/iversion.h
@@ -112,6 +112,30 @@  inode_peek_iversion_raw(const struct inode *inode)
 	return atomic64_read(&inode->i_version);
 }
 
+/**
+ * inode_set_max_iversion_raw - update i_version new value is larger
+ * @inode: inode to set
+ * @val: new i_version to set
+ *
+ * Some self-managed filesystems (e.g Ceph) will only update the i_version
+ * value if the new value is larger than the one we already have.
+ */
+static inline void
+inode_set_max_iversion_raw(struct inode *inode, u64 val)
+{
+	u64 cur, old;
+
+	cur = inode_peek_iversion_raw(inode);
+	for (;;) {
+		if (cur > val)
+			break;
+		old = atomic64_cmpxchg(&inode->i_version, cur, val);
+		if (likely(old == cur))
+			break;
+		cur = old;
+	}
+}
+
 /**
  * inode_set_iversion - set i_version to a particular value
  * @inode: inode to set