Merge tag 'vfs-6.16-rc2.fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs

Pull vfs fixes from Christian Brauner:

 - Fix the AT_HANDLE_CONNECTABLE option so filesystems that don't know
   how to decode a connected non-dir dentry fail the request

 - Use repr(transparent) to ensure identical layout between the C and
   Rust implementation of struct file

 - Add a missing xas_pause() into the dax code employing
   wait_entry_unlocked_exclusive()

 - Fix FOP_DONTCACHE which we disabled for v6.15.

   A folio could get redirtied and/or scheduled for writeback after the
   initial dropbehind test. Change the test accordingly to handle these
   cases so we can re-enable FOP_DONTCACHE again

* tag 'vfs-6.16-rc2.fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs:
  exportfs: require ->fh_to_parent() to encode connectable file handles
  rust: file: improve safety comments
  rust: file: mark `LocalFile` as `repr(transparent)`
  fs/dax: Fix "don't skip locked entries when scanning entries"
  iomap: don't lose folio dropbehind state for overwrites
  mm/filemap: unify dropbehind flag testing and clearing
  mm/filemap: unify read/write dropbehind naming
  Revert "Disable FOP_DONTCACHE for now due to bugs"
  mm/filemap: use filemap_end_dropbehind() for read invalidation
  mm/filemap: gate dropbehind invalidate on folio !dirty && !writeback

3 files changed, 15 insertions, 2 deletions

diff --git a/include/linux/exportfs.h b/include/linux/exportfs.h
index fc93f0abf513..25c4a5afbd44 100644
--- a/include/linux/exportfs.h
+++ b/include/linux/exportfs.h
@@ -314,6 +314,9 @@ static inline bool exportfs_can_decode_fh(const struct export_operations *nop)
 static inline bool exportfs_can_encode_fh(const struct export_operations *nop,
 					  int fh_flags)
 {
+	if (!nop)
+		return false;
+
 	/*
 	 * If a non-decodeable file handle was requested, we only need to make
 	 * sure that filesystem did not opt-out of encoding fid.
@@ -322,6 +325,13 @@ static inline bool exportfs_can_encode_fh(const struct export_operations *nop,
 		return exportfs_can_encode_fid(nop);
 
 	/*
+	 * If a connectable file handle was requested, we need to make sure that
+	 * filesystem can also decode connected file handles.
+	 */
+	if ((fh_flags & EXPORT_FH_CONNECTABLE) && !nop->fh_to_parent)
+		return false;
+
+	/*
 	 * If a decodeable file handle was requested, we need to make sure that
 	 * filesystem can also decode file handles.
 	 */
diff --git a/include/linux/fs.h b/include/linux/fs.h
index da86fcb11882..96c7925a6551 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2207,7 +2207,7 @@ struct file_operations {
 /* Supports asynchronous lock callbacks */
 #define FOP_ASYNC_LOCK		((__force fop_flags_t)(1 << 6))
 /* File system supports uncached read/write buffered IO */
-#define FOP_DONTCACHE		0 /* ((__force fop_flags_t)(1 << 7)) */
+#define FOP_DONTCACHE		((__force fop_flags_t)(1 << 7))
 
 /* Wrap a directory iterator that needs exclusive inode access */
 int wrap_directory_iterator(struct file *, struct dir_context *,
diff --git a/include/linux/iomap.h b/include/linux/iomap.h
index 68416b135151..522644d62f30 100644
--- a/include/linux/iomap.h
+++ b/include/linux/iomap.h
@@ -377,13 +377,16 @@ sector_t iomap_bmap(struct address_space *mapping, sector_t bno,
 #define IOMAP_IOEND_BOUNDARY		(1U << 2)
 /* is direct I/O */
 #define IOMAP_IOEND_DIRECT		(1U << 3)
+/* is DONTCACHE I/O */
+#define IOMAP_IOEND_DONTCACHE		(1U << 4)
 
 /*
  * Flags that if set on either ioend prevent the merge of two ioends.
  * (IOMAP_IOEND_BOUNDARY also prevents merges, but only one-way)
  */
 #define IOMAP_IOEND_NOMERGE_FLAGS \
-	(IOMAP_IOEND_SHARED | IOMAP_IOEND_UNWRITTEN | IOMAP_IOEND_DIRECT)
+	(IOMAP_IOEND_SHARED | IOMAP_IOEND_UNWRITTEN | IOMAP_IOEND_DIRECT | \
+	 IOMAP_IOEND_DONTCACHE)
 
 /*
  * Structure for writeback I/O completions.