fuse3/fuse-3.16.1-Make-expire-only-function-fail-if-no-kernel-support-.patch

From 51bc827df873d9ff4069b83796cd32fcb6bd659e Mon Sep 17 00:00:00 2001
From: HereThereBeDragons <HereThereBeDragons@users.noreply.github.com>
Date: Fri, 30 Jun 2023 14:57:06 +0200
Subject: [PATCH] Make expire only function fail if no kernel support (#789)

---
 include/fuse_common.h   |    2 +-
 include/fuse_lowlevel.h |   28 ++++++++++++++--------------
 lib/fuse_lowlevel.c     |   41 ++++++++++++++++++++++++++++++++++++-----
 3 files changed, 51 insertions(+), 20 deletions(-)

--- a/include/fuse_common.h
+++ b/include/fuse_common.h
@@ -395,7 +395,7 @@ struct fuse_loop_config {
 #define FUSE_CAP_EXPLICIT_INVAL_DATA    (1 << 25)
 
 /**
- * Indicates support that dentries can be expired or invalidated.
+ * Indicates support that dentries can be expired.
  * 
  * Expiring dentries, instead of invalidating them, makes a difference for 
  * overmounted dentries, where plain invalidation would detach all submounts 
--- a/include/fuse_lowlevel.h
+++ b/include/fuse_lowlevel.h
@@ -128,11 +128,12 @@ struct fuse_forget_data {
 };
 
 /**
- * Flags for fuse_lowlevel_notify_expire_entry()
+ * Flags for fuse_lowlevel_notify_entry()
  * 0 = invalidate entry
  * FUSE_LL_EXPIRE_ONLY = expire entry
 */
-enum fuse_expire_flags {
+enum fuse_notify_entry_flags {
+	FUSE_LL_INVALIDATE = 0,
 	FUSE_LL_EXPIRE_ONLY	= (1 << 0),
 };
 
@@ -1657,8 +1658,7 @@ int fuse_lowlevel_notify_inval_inode(str
 				     off_t off, off_t len);
 
 /**
- * Notify to invalidate parent attributes and the dentry matching
- * parent/name
+ * Notify to invalidate parent attributes and the dentry matching parent/name
  *
  * To avoid a deadlock this function must not be called in the
  * execution path of a related filesytem operation or within any code
@@ -1685,14 +1685,13 @@ int fuse_lowlevel_notify_inval_entry(str
 				     const char *name, size_t namelen);
 
 /**
- * Notify to expire or invalidate parent attributes and the dentry 
- * matching parent/name
+ * Notify to expire parent attributes and the dentry matching parent/name
  * 
- * Underlying function for fuse_lowlevel_notify_inval_entry().
+ * Same restrictions apply as for fuse_lowlevel_notify_inval_entry()
  * 
- * In addition to invalidating an entry, it also allows to expire an entry.
- * In that case, the entry is not forcefully removed from kernel cache 
- * but instead the next access to it forces a lookup from the filesystem.
+ * Compared to invalidating an entry, expiring the entry results not in a
+ * forceful removal of that entry from kernel cache but instead the next access
+ * to it forces a lookup from the filesystem.
  * 
  * This makes a difference for overmounted dentries, where plain invalidation
  * would detach all submounts before dropping the dentry from the cache. 
@@ -1703,17 +1702,18 @@ int fuse_lowlevel_notify_inval_entry(str
  * so invalidation will only be triggered for the non-overmounted case.
  * The dentry could also be mounted in a different mount instance, in which case
  * any submounts will still be detached.
+ * 
+ * Added in FUSE protocol version 7.38. If the kernel does not support
+ * this (or a newer) version, the function will return -ENOSYS and do nothing.
  *
  * @param se the session object
  * @param parent inode number
  * @param name file name
  * @param namelen strlen() of file name
- * @param flags flags to control if the entry should be expired or invalidated
- * @return zero for success, -errno for failure
+ * @return zero for success, -errno for failure, -enosys if no kernel support
 */
 int fuse_lowlevel_notify_expire_entry(struct fuse_session *se, fuse_ino_t parent,
-                                      const char *name, size_t namelen,
-                                      enum fuse_expire_flags flags);
+                                      const char *name, size_t namelen);
 
 /**
  * This function behaves like fuse_lowlevel_notify_inval_entry() with
--- a/lib/fuse_lowlevel.c
+++ b/lib/fuse_lowlevel.c
@@ -2257,9 +2257,28 @@ int fuse_lowlevel_notify_inval_inode(str
 	return send_notify_iov(se, FUSE_NOTIFY_INVAL_INODE, iov, 2);
 }
 
-int fuse_lowlevel_notify_expire_entry(struct fuse_session *se, fuse_ino_t parent,
-				      const char *name, size_t namelen,
-				      enum fuse_expire_flags flags)
+/**
+ * Notify parent attributes and the dentry matching parent/name
+ * 
+ * Underlying base function for fuse_lowlevel_notify_inval_entry() and
+ * fuse_lowlevel_notify_expire_entry().
+ * 
+ * @warning
+ * Only checks if fuse_lowlevel_notify_inval_entry() is supported by
+ * the kernel. All other flags will fall back to 
+ * fuse_lowlevel_notify_inval_entry() if not supported!
+ * DO THE PROPER CHECKS IN THE DERIVED FUNCTION!
+ *
+ * @param se the session object
+ * @param parent inode number
+ * @param name file name
+ * @param namelen strlen() of file name
+ * @param flags flags to control if the entry should be expired or invalidated
+ * @return zero for success, -errno for failure
+*/
+static int fuse_lowlevel_notify_entry(struct fuse_session *se, fuse_ino_t parent,
+							const char *name, size_t namelen,
+							enum fuse_notify_entry_flags flags)
 {
 	struct fuse_notify_inval_entry_out outarg;
 	struct iovec iov[3];
@@ -2285,9 +2304,21 @@ int fuse_lowlevel_notify_expire_entry(st
 }
 
 int fuse_lowlevel_notify_inval_entry(struct fuse_session *se, fuse_ino_t parent,
-				     const char *name, size_t namelen)
+						 const char *name, size_t namelen)
+{
+	return fuse_lowlevel_notify_entry(se, parent, name, namelen, FUSE_LL_INVALIDATE);
+}
+
+int fuse_lowlevel_notify_expire_entry(struct fuse_session *se, fuse_ino_t parent,
+							const char *name, size_t namelen)
 {
-	return fuse_lowlevel_notify_expire_entry(se, parent, name, namelen, 0);
+	if (!se)
+		return -EINVAL;
+
+	if (!(se->conn.capable & FUSE_CAP_EXPIRE_ONLY))
+		return -ENOSYS;
+
+	return fuse_lowlevel_notify_entry(se, parent, name, namelen, FUSE_LL_EXPIRE_ONLY);
 }