Merge branch 'master' into test

* master: (1190 commits)
  ASoC: stm32: add of dependency for stm32 drivers
  ASoC: mt8173-rt5650: fix child-node lookup
  ASoC: dapm: fix debugfs read using path->connected
  platform/x86: samsung-laptop: Re-use DEFINE_SHOW_ATTRIBUTE() macro
  platform/x86: ideapad-laptop: Re-use DEFINE_SHOW_ATTRIBUTE() macro
  platform/x86: dell-laptop: Re-use DEFINE_SHOW_ATTRIBUTE() macro
  seq_file: Introduce DEFINE_SHOW_ATTRIBUTE() helper macro
  Documentation/sysctl/user.txt: fix typo
  MAINTAINERS: update ARM/QUALCOMM SUPPORT patterns
  MAINTAINERS: update various PALM patterns
  MAINTAINERS: update "ARM/OXNAS platform support" patterns
  MAINTAINERS: update Cortina/Gemini patterns
  MAINTAINERS: remove ARM/CLKDEV SUPPORT file pattern
  MAINTAINERS: remove ANDROID ION pattern
  mm: docs: add blank lines to silence sphinx "Unexpected indentation" errors
  mm: docs: fix parameter names mismatch
  mm: docs: fixup punctuation
  pipe: read buffer limits atomically
  pipe: simplify round_pipe_size()
  pipe: reject F_SETPIPE_SZ with size over UINT_MAX
  ...

1 files changed, 25 insertions, 6 deletions

diff --git a/fs/overlayfs/Kconfig b/fs/overlayfs/Kconfig
index 5ac415466861..406e72de88f6 100644
--- a/fs/overlayfs/Kconfig
+++ b/fs/overlayfs/Kconfig
@@ -47,9 +47,28 @@ config OVERLAY_FS_INDEX
 	  The inodes index feature prevents breaking of lower hardlinks on copy
 	  up.
 
-	  Note, that the inodes index feature is read-only backward compatible.
-	  That is, mounting an overlay which has an index dir on a kernel that
-	  doesn't support this feature read-only, will not have any negative
-	  outcomes.  However, mounting the same overlay with an old kernel
-	  read-write and then mounting it again with a new kernel, will have
-	  unexpected results.
+	  Note, that the inodes index feature is not backward compatible.
+	  That is, mounting an overlay which has an inodes index on a kernel
+	  that doesn't support this feature will have unexpected results.
+
+config OVERLAY_FS_NFS_EXPORT
+	bool "Overlayfs: turn on NFS export feature by default"
+	depends on OVERLAY_FS
+	depends on OVERLAY_FS_INDEX
+	help
+	  If this config option is enabled then overlay filesystems will use
+	  the inodes index dir to decode overlay NFS file handles by default.
+	  In this case, it is still possible to turn off NFS export support
+	  globally with the "nfs_export=off" module option or on a filesystem
+	  instance basis with the "nfs_export=off" mount option.
+
+	  The NFS export feature creates an index on copy up of every file and
+	  directory.  This full index is used to detect overlay filesystems
+	  inconsistencies on lookup, like redirect from multiple upper dirs to
+	  the same lower dir.  The full index may incur some overhead on mount
+	  time, especially when verifying that directory file handles are not
+	  stale.
+
+	  Note, that the NFS export feature is not backward compatible.
+	  That is, mounting an overlay which has a full index on a kernel
+	  that doesn't support this feature will have unexpected results.