From bdc10bdf4b03dccaead3cdb90b3963d416de6fe0 Mon Sep 17 00:00:00 2001 From: Amir Goldstein Date: Tue, 12 Dec 2023 09:15:47 +0200 Subject: 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 Signed-off-by: Amir Goldstein --- Documentation/filesystems/overlayfs.rst | 27 +++++++++++++++------------ 1 file changed, 15 insertions(+), 12 deletions(-) (limited to 'Documentation') diff --git a/Documentation/filesystems/overlayfs.rst b/Documentation/filesystems/overlayfs.rst index 0407f361f32a..926396fdc5eb 100644 --- a/Documentation/filesystems/overlayfs.rst +++ b/Documentation/filesystems/overlayfs.rst @@ -39,7 +39,7 @@ objects in the original filesystem. On 64bit systems, even if all overlay layers are not on the same underlying filesystem, the same compliant behavior could be achieved with the "xino" feature. The "xino" feature composes a unique object -identifier from the real object st_ino and an underlying fsid index. +identifier from the real object st_ino and an underlying fsid number. The "xino" feature uses the high inode number bits for fsid, because the underlying filesystems rarely use the high inode number bits. In case the underlying inode number does overflow into the high xino bits, overlay @@ -356,7 +356,7 @@ as an octal characters (\072) when displayed in /proc/self/mountinfo. Metadata only copy up --------------------- -When metadata only copy up feature is enabled, overlayfs will only copy +When the "metacopy" feature is enabled, overlayfs will only copy up metadata (as opposed to whole file), when a metadata specific operation like chown/chmod is performed. Full file will be copied up later when file is opened for WRITE operation. @@ -492,27 +492,27 @@ though it will not result in a crash or deadlock. Mounting an overlay using an upper layer path, where the upper layer path was previously used by another mounted overlay in combination with a -different lower layer path, is allowed, unless the "inodes index" feature -or "metadata only copy up" feature is enabled. +different lower layer path, is allowed, unless the "index" or "metacopy" +features are enabled. -With the "inodes index" feature, on the first time mount, an NFS file +With the "index" feature, on the first time mount, an NFS file handle of the lower layer root directory, along with the UUID of the lower filesystem, are encoded and stored in the "trusted.overlay.origin" extended attribute on the upper layer root directory. On subsequent mount attempts, the lower root directory file handle and lower filesystem UUID are compared to the stored origin in upper root directory. On failure to verify the lower root origin, mount will fail with ESTALE. An overlayfs mount with -"inodes index" enabled will fail with EOPNOTSUPP if the lower filesystem +"index" enabled will fail with EOPNOTSUPP if the lower filesystem does not support NFS export, lower filesystem does not have a valid UUID or if the upper filesystem does not support extended attributes. -For "metadata only copy up" feature there is no verification mechanism at +For the "metacopy" feature, there is no verification mechanism at mount time. So if same upper is mounted with different set of lower, mount probably will succeed but expect the unexpected later on. So don't do it. It is quite a common practice to copy overlay layers to a different directory tree on the same or different underlying filesystem, and even -to a different machine. With the "inodes index" feature, trying to mount +to a different machine. With the "index" feature, trying to mount the copied layers will fail the verification of the lower root file handle. Nesting overlayfs mounts @@ -560,7 +560,8 @@ file for write or truncating the file will not be denied with ETXTBSY. The following options allow overlayfs to act more like a standards compliant filesystem: -1) "redirect_dir" +redirect_dir +```````````` Enabled with the mount option or module option: "redirect_dir=on" or with the kernel config option CONFIG_OVERLAY_FS_REDIRECT_DIR=y. @@ -568,7 +569,8 @@ the kernel config option CONFIG_OVERLAY_FS_REDIRECT_DIR=y. If this feature is disabled, then rename(2) on a lower or merged directory will fail with EXDEV ("Invalid cross-device link"). -2) "inode index" +index +````` Enabled with the mount option or module option "index=on" or with the kernel config option CONFIG_OVERLAY_FS_INDEX=y. @@ -577,7 +579,8 @@ If this feature is disabled and 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. -3) "xino" +xino +```` Enabled with the mount option "xino=auto" or "xino=on", with the module option "xino_auto=on" or with the kernel config option @@ -604,7 +607,7 @@ a crash or deadlock. Offline changes, when the overlay is not mounted, are allowed to the upper tree. Offline changes to the lower tree are only allowed if the -"metadata only copy up", "inode index", "xino" and "redirect_dir" features +"metacopy", "index", "xino" and "redirect_dir" features have not been used. If the lower tree is modified and any of these features has been used, the behavior of the overlay is undefined, though it will not result in a crash or deadlock. -- cgit v1.2.3