diff options
Diffstat (limited to 'Documentation/filesystems')
| -rw-r--r-- | Documentation/filesystems/files.rst | 2 | ||||
| -rw-r--r-- | Documentation/filesystems/locking.rst | 2 | ||||
| -rw-r--r-- | Documentation/filesystems/overlayfs.rst | 16 | ||||
| -rw-r--r-- | Documentation/filesystems/vfs.rst | 16 |
4 files changed, 22 insertions, 14 deletions
diff --git a/Documentation/filesystems/files.rst b/Documentation/filesystems/files.rst index 9e38e4c221ca..eb770f891b27 100644 --- a/Documentation/filesystems/files.rst +++ b/Documentation/filesystems/files.rst @@ -116,7 +116,7 @@ before and after the reference count increment. This pattern can be seen in get_file_rcu() and __files_get_rcu(). In addition, it isn't possible to access or check fields in struct file -without first aqcuiring a reference on it under rcu lookup. Not doing +without first acquiring a reference on it under rcu lookup. Not doing that was always very dodgy and it was only usable for non-pointer data in struct file. With SLAB_TYPESAFE_BY_RCU it is necessary that callers either first acquire a reference or they must hold the files_lock of the diff --git a/Documentation/filesystems/locking.rst b/Documentation/filesystems/locking.rst index d5bf4b6b7509..e664061ed55d 100644 --- a/Documentation/filesystems/locking.rst +++ b/Documentation/filesystems/locking.rst @@ -29,7 +29,7 @@ prototypes:: char *(*d_dname)((struct dentry *dentry, char *buffer, int buflen); struct vfsmount *(*d_automount)(struct path *path); int (*d_manage)(const struct path *, bool); - struct dentry *(*d_real)(struct dentry *, const struct inode *); + struct dentry *(*d_real)(struct dentry *, enum d_real_type type); locking rules: diff --git a/Documentation/filesystems/overlayfs.rst b/Documentation/filesystems/overlayfs.rst index 1c244866041a..165514401441 100644 --- a/Documentation/filesystems/overlayfs.rst +++ b/Documentation/filesystems/overlayfs.rst @@ -145,7 +145,9 @@ filesystem, an overlay filesystem needs to record in the upper filesystem that files have been removed. This is done using whiteouts and opaque directories (non-directories are always opaque). -A whiteout is created as a character device with 0/0 device number. +A whiteout is created as a character device with 0/0 device number or +as a zero-size regular file with the xattr "trusted.overlay.whiteout". + When a whiteout is found in the upper level of a merged directory, any matching name in the lower level is ignored, and the whiteout itself is also hidden. @@ -154,6 +156,13 @@ A directory is made opaque by setting the xattr "trusted.overlay.opaque" to "y". Where the upper filesystem contains an opaque directory, any directory in the lower filesystem with the same name is ignored. +An opaque directory should not conntain any whiteouts, because they do not +serve any purpose. A merge directory containing regular files with the xattr +"trusted.overlay.whiteout", should be additionally marked by setting the xattr +"trusted.overlay.opaque" to "x" on the merge directory itself. +This is needed to avoid the overhead of checking the "trusted.overlay.whiteout" +on all entries during readdir in the common case. + readdir ------- @@ -534,8 +543,9 @@ A lower dir with a regular whiteout will always be handled by the overlayfs mount, so to support storing an effective whiteout file in an overlayfs mount an alternative form of whiteout is supported. This form is a regular, zero-size file with the "overlay.whiteout" xattr set, inside a directory with the -"overlay.whiteouts" xattr set. Such whiteouts are never created by overlayfs, -but can be used by userspace tools (like containers) that generate lower layers. +"overlay.opaque" xattr set to "x" (see `whiteouts and opaque directories`_). +These alternative whiteouts are never created by overlayfs, but can be used by +userspace tools (like containers) that generate lower layers. These alternative whiteouts can be escaped using the standard xattr escape mechanism in order to properly nest to any depth. diff --git a/Documentation/filesystems/vfs.rst b/Documentation/filesystems/vfs.rst index eebcc0f9e2bc..6e903a903f8f 100644 --- a/Documentation/filesystems/vfs.rst +++ b/Documentation/filesystems/vfs.rst @@ -1264,7 +1264,7 @@ defined: char *(*d_dname)(struct dentry *, char *, int); struct vfsmount *(*d_automount)(struct path *); int (*d_manage)(const struct path *, bool); - struct dentry *(*d_real)(struct dentry *, const struct inode *); + struct dentry *(*d_real)(struct dentry *, enum d_real_type type); }; ``d_revalidate`` @@ -1419,16 +1419,14 @@ defined: the dentry being transited from. ``d_real`` - overlay/union type filesystems implement this method to return - one of the underlying dentries hidden by the overlay. It is - used in two different modes: + overlay/union type filesystems implement this method to return one + of the underlying dentries of a regular file hidden by the overlay. - Called from file_dentry() it returns the real dentry matching - the inode argument. The real dentry may be from a lower layer - already copied up, but still referenced from the file. This - mode is selected with a non-NULL inode argument. + The 'type' argument takes the values D_REAL_DATA or D_REAL_METADATA + for returning the real underlying dentry that refers to the inode + hosting the file's data or metadata respectively. - With NULL inode the topmost real underlying dentry is returned. + For non-regular files, the 'dentry' argument is returned. Each dentry has a pointer to its parent dentry, as well as a hash list of child dentries. Child dentries are basically like files in a |