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-rw-r--r--Documentation/filesystems/overlayfs.txt26
1 files changed, 22 insertions, 4 deletions
diff --git a/Documentation/filesystems/overlayfs.txt b/Documentation/filesystems/overlayfs.txt
index bcbf9710e4af..634d03e20c2d 100644
--- a/Documentation/filesystems/overlayfs.txt
+++ b/Documentation/filesystems/overlayfs.txt
@@ -66,7 +66,7 @@ At mount time, the two directories given as mount options "lowerdir" and
"upperdir" are combined into a merged directory:
mount -t overlay overlay -olowerdir=/lower,upperdir=/upper,\
-workdir=/work /merged
+ workdir=/work /merged
The "workdir" needs to be an empty directory on the same filesystem
as upperdir.
@@ -118,6 +118,7 @@ programs.
seek offsets are assigned sequentially when the directories are read.
Thus if
+
- read part of a directory
- remember an offset, and close the directory
- re-open the directory some time later
@@ -130,6 +131,23 @@ directory.
Readdir on directories that are not merged is simply handled by the
underlying directory (upper or lower).
+renaming directories
+--------------------
+
+When renaming a directory that is on the lower layer or merged (i.e. the
+directory was not created on the upper layer to start with) overlayfs can
+handle it in two different ways:
+
+1. return EXDEV error: this error is returned by rename(2) when trying to
+ move a file or directory across filesystem boundaries. Hence
+ applications are usually prepared to hande this error (mv(1) for example
+ recursively copies the directory tree). This is the default behavior.
+
+2. If the "redirect_dir" feature is enabled, then the directory will be
+ copied up (but not the contents). Then the "trusted.overlay.redirect"
+ extended attribute is set to the path of the original location from the
+ root of the overlay. Finally the directory is moved to the new
+ location.
Non-directories
---------------
@@ -185,13 +203,13 @@ filesystem, so both st_dev and st_ino of the file may change.
Any open files referring to this inode will access the old data.
-Any file locks (and leases) obtained before copy_up will not apply
-to the copied up file.
-
If a file with multiple hard links is copied up, then this will
"break" the link. Changes will not be propagated to other names
referring to the same inode.
+Unless "redirect_dir" feature is enabled, rename(2) on a lower or merged
+directory will fail with EXDEV.
+
Changes to underlying filesystems
---------------------------------