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overlayfs.rst: use consistent feature names
Use the feature names "metacopy" and "index" consistently throughout the document. Covert the numbered list of features "redirect_dir", "index", "xino" to section headings, so that those features could be referenced in the document by their name. Reviewed-by: Bagas Sanjaya <bagasdotme@gmail.com> Signed-off-by: Amir Goldstein <amir73il@gmail.com>
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@ -39,7 +39,7 @@ objects in the original filesystem.
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On 64bit systems, even if all overlay layers are not on the same
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underlying filesystem, the same compliant behavior could be achieved
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with the "xino" feature. The "xino" feature composes a unique object
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identifier from the real object st_ino and an underlying fsid index.
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identifier from the real object st_ino and an underlying fsid number.
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The "xino" feature uses the high inode number bits for fsid, because the
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underlying filesystems rarely use the high inode number bits. In case
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the underlying inode number does overflow into the high xino bits, overlay
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@ -356,7 +356,7 @@ as an octal characters (\072) when displayed in /proc/self/mountinfo.
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Metadata only copy up
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---------------------
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When metadata only copy up feature is enabled, overlayfs will only copy
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When the "metacopy" feature is enabled, overlayfs will only copy
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up metadata (as opposed to whole file), when a metadata specific operation
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like chown/chmod is performed. Full file will be copied up later when
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file is opened for WRITE operation.
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@ -492,27 +492,27 @@ though it will not result in a crash or deadlock.
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Mounting an overlay using an upper layer path, where the upper layer path
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was previously used by another mounted overlay in combination with a
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different lower layer path, is allowed, unless the "inodes index" feature
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or "metadata only copy up" feature is enabled.
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different lower layer path, is allowed, unless the "index" or "metacopy"
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features are enabled.
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With the "inodes index" feature, on the first time mount, an NFS file
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With the "index" feature, on the first time mount, an NFS file
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handle of the lower layer root directory, along with the UUID of the lower
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filesystem, are encoded and stored in the "trusted.overlay.origin" extended
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attribute on the upper layer root directory. On subsequent mount attempts,
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the lower root directory file handle and lower filesystem UUID are compared
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to the stored origin in upper root directory. On failure to verify the
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lower root origin, mount will fail with ESTALE. An overlayfs mount with
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"inodes index" enabled will fail with EOPNOTSUPP if the lower filesystem
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"index" enabled will fail with EOPNOTSUPP if the lower filesystem
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does not support NFS export, lower filesystem does not have a valid UUID or
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if the upper filesystem does not support extended attributes.
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For "metadata only copy up" feature there is no verification mechanism at
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For the "metacopy" feature, there is no verification mechanism at
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mount time. So if same upper is mounted with different set of lower, mount
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probably will succeed but expect the unexpected later on. So don't do it.
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It is quite a common practice to copy overlay layers to a different
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directory tree on the same or different underlying filesystem, and even
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to a different machine. With the "inodes index" feature, trying to mount
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to a different machine. With the "index" feature, trying to mount
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the copied layers will fail the verification of the lower root file handle.
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Nesting overlayfs mounts
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@ -560,7 +560,8 @@ file for write or truncating the file will not be denied with ETXTBSY.
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The following options allow overlayfs to act more like a standards
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compliant filesystem:
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1) "redirect_dir"
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redirect_dir
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````````````
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Enabled with the mount option or module option: "redirect_dir=on" or with
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the kernel config option CONFIG_OVERLAY_FS_REDIRECT_DIR=y.
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@ -568,7 +569,8 @@ the kernel config option CONFIG_OVERLAY_FS_REDIRECT_DIR=y.
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If this feature is disabled, then rename(2) on a lower or merged directory
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will fail with EXDEV ("Invalid cross-device link").
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2) "inode index"
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index
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`````
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Enabled with the mount option or module option "index=on" or with the
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kernel config option CONFIG_OVERLAY_FS_INDEX=y.
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@ -577,7 +579,8 @@ If this feature is disabled and a file with multiple hard links is copied
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up, then this will "break" the link. Changes will not be propagated to
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other names referring to the same inode.
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3) "xino"
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xino
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````
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Enabled with the mount option "xino=auto" or "xino=on", with the module
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option "xino_auto=on" or with the kernel config option
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@ -604,7 +607,7 @@ a crash or deadlock.
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Offline changes, when the overlay is not mounted, are allowed to the
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upper tree. Offline changes to the lower tree are only allowed if the
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"metadata only copy up", "inode index", "xino" and "redirect_dir" features
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"metacopy", "index", "xino" and "redirect_dir" features
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have not been used. If the lower tree is modified and any of these
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features has been used, the behavior of the overlay is undefined,
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though it will not result in a crash or deadlock.
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