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kernel: backport overlayfs v11 to 3.0 and 2.6.39 

Should fix whiteout issues and missing files when using extroot.

SVN-Revision: 29727
owl
Jonas Gorski 2012-01-13 14:42:53 +00:00
parent c560444a58
commit f3f1075655
2 changed files with 2593 additions and 2154 deletions
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4050
target/linux/generic/patches-2.6.39/100-overlayfs.patch → target/linux/generic/patches-2.6.39/100-overlayfs_v11.patch
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File diff suppressed because it is too large Load Diff

687
target/linux/generic/patches-3.0/100-overlayfs_v10.patch → target/linux/generic/patches-3.0/100-overlayfs_v11.patch
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@ -1,3 +1,283 @@
--- /dev/null
+++ b/Documentation/filesystems/overlayfs.txt
@@ -0,0 +1,199 @@
+Written by: Neil Brown <neilb@suse.de>
+
+Overlay Filesystem
+==================
+
+This document describes a prototype for a new approach to providing
+overlay-filesystem functionality in Linux (sometimes referred to as
+union-filesystems). An overlay-filesystem tries to present a
+filesystem which is the result over overlaying one filesystem on top
+of the other.
+
+The result will inevitably fail to look exactly like a normal
+filesystem for various technical reasons. The expectation is that
+many use cases will be able to ignore these differences.
+
+This approach is 'hybrid' because the objects that appear in the
+filesystem do not all appear to belong to that filesystem. In many
+cases an object accessed in the union will be indistinguishable
+from accessing the corresponding object from the original filesystem.
+This is most obvious from the 'st_dev' field returned by stat(2).
+
+While directories will report an st_dev from the overlay-filesystem,
+all non-directory objects will report an st_dev from the lower or
+upper filesystem that is providing the object. Similarly st_ino will
+only be unique when combined with st_dev, and both of these can change
+over the lifetime of a non-directory object. Many applications and
+tools ignore these values and will not be affected.
+
+Upper and Lower
+---------------
+
+An overlay filesystem combines two filesystems - an 'upper' filesystem
+and a 'lower' filesystem. When a name exists in both filesystems, the
+object in the 'upper' filesystem is visible while the object in the
+'lower' filesystem is either hidden or, in the case of directories,
+merged with the 'upper' object.
+
+It would be more correct to refer to an upper and lower 'directory
+tree' rather than 'filesystem' as it is quite possible for both
+directory trees to be in the same filesystem and there is no
+requirement that the root of a filesystem be given for either upper or
+lower.
+
+The lower filesystem can be any filesystem supported by Linux and does
+not need to be writable. The lower filesystem can even be another
+overlayfs. The upper filesystem will normally be writable and if it
+is it must support the creation of trusted.* extended attributes, and
+must provide valid d_type in readdir responses, at least for symbolic
+links - so NFS is not suitable.
+
+A read-only overlay of two read-only filesystems may use any
+filesystem type.
+
+Directories
+-----------
+
+Overlaying mainly involved directories. If a given name appears in both
+upper and lower filesystems and refers to a non-directory in either,
+then the lower object is hidden - the name refers only to the upper
+object.
+
+Where both upper and lower objects are directories, a merged directory
+is formed.
+
+At mount time, the two directories given as mount options are combined
+into a merged directory:
+
+ mount -t overlayfs overlayfs -olowerdir=/lower,upperdir=/upper /overlay
+
+Then whenever a lookup is requested in such a merged directory, the
+lookup is performed in each actual directory and the combined result
+is cached in the dentry belonging to the overlay filesystem. If both
+actual lookups find directories, both are stored and a merged
+directory is created, otherwise only one is stored: the upper if it
+exists, else the lower.
+
+Only the lists of names from directories are merged. Other content
+such as metadata and extended attributes are reported for the upper
+directory only. These attributes of the lower directory are hidden.
+
+whiteouts and opaque directories
+--------------------------------
+
+In order to support rm and rmdir without changing the lower
+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).
+
+The overlay filesystem uses extended attributes with a
+"trusted.overlay." prefix to record these details.
+
+A whiteout is created as a symbolic link with target
+"(overlay-whiteout)" and with xattr "trusted.overlay.whiteout" set to "y".
+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.
+
+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.
+
+readdir
+-------
+
+When a 'readdir' request is made on a merged directory, the upper and
+lower directories are each read and the name lists merged in the
+obvious way (upper is read first, then lower - entries that already
+exist are not re-added). This merged name list is cached in the
+'struct file' and so remains as long as the file is kept open. If the
+directory is opened and read by two processes at the same time, they
+will each have separate caches. A seekdir to the start of the
+directory (offset 0) followed by a readdir will cause the cache to be
+discarded and rebuilt.
+
+This means that changes to the merged directory do not appear while a
+directory is being read. This is unlikely to be noticed by many
+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
+ - seek to the remembered offset
+
+there may be little correlation between the old and new locations in
+the list of filenames, particularly if anything has changed in the
+directory.
+
+Readdir on directories that are not merged is simply handled by the
+underlying directory (upper or lower).
+
+
+Non-directories
+---------------
+
+Objects that are not directories (files, symlinks, device-special
+files etc.) are presented either from the upper or lower filesystem as
+appropriate. When a file in the lower filesystem is accessed in a way
+the requires write-access, such as opening for write access, changing
+some metadata etc., the file is first copied from the lower filesystem
+to the upper filesystem (copy_up). Note that creating a hard-link
+also requires copy_up, though of course creation of a symlink does
+not.
+
+The copy_up may turn out to be unnecessary, for example if the file is
+opened for read-write but the data is not modified.
+
+The copy_up process first makes sure that the containing directory
+exists in the upper filesystem - creating it and any parents as
+necessary. It then creates the object with the same metadata (owner,
+mode, mtime, symlink-target etc.) and then if the object is a file, the
+data is copied from the lower to the upper filesystem. Finally any
+extended attributes are copied up.
+
+Once the copy_up is complete, the overlay filesystem simply
+provides direct access to the newly created file in the upper
+filesystem - future operations on the file are barely noticed by the
+overlay filesystem (though an operation on the name of the file such as
+rename or unlink will of course be noticed and handled).
+
+
+Non-standard behavior
+---------------------
+
+The copy_up operation essentially creates a new, identical file and
+moves it over to the old name. The new file may be on a different
+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 and
+metadata. Similarly any file locks obtained before copy_up will not
+apply to the copied up file.
+
+On a file is opened with O_RDONLY fchmod(2), fchown(2), futimesat(2)
+and fsetxattr(2) will fail with EROFS.
+
+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.
+
+Symlinks in /proc/PID/ and /proc/PID/fd which point to a non-directory
+object in overlayfs will not contain vaid absolute paths, only
+relative paths leading up to the filesystem's root. This will be
+fixed in the future.
+
+Some operations are not atomic, for example a crash during copy_up or
+rename will leave the filesystem in an inconsitent state. This will
+be addressed in the future.
+
+Changes to underlying filesystems
+---------------------------------
+
+Offline changes, when the overlay is not mounted, are allowed to either
+the upper or the lower trees.
+
+Changes to the underlying filesystems while part of a mounted overlay
+filesystem are not allowed. If the underlying filesystem is changed,
+the behavior of the overlay is undefined, though it will not result in
+a crash or deadlock.
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -4727,6 +4727,13 @@ F: drivers/scsi/osd/
F: include/scsi/osd_*
F: fs/exofs/
+OVERLAYFS FILESYSTEM
+M: Miklos Szeredi <miklos@szeredi.hu>
+L: linux-fsdevel@vger.kernel.org
+S: Supported
+F: fs/overlayfs/*
+F: Documentation/filesystems/overlayfs.txt
+
P54 WIRELESS DRIVER
M: Christian Lamparter <chunkeey@googlemail.com>
L: linux-wireless@vger.kernel.org
--- a/fs/Kconfig
+++ b/fs/Kconfig
@@ -63,6 +63,7 @@ source "fs/quota/Kconfig"
source "fs/autofs4/Kconfig"
source "fs/fuse/Kconfig"
+source "fs/overlayfs/Kconfig"
config CUSE
tristate "Character device in Userspace support"
--- a/fs/Makefile
+++ b/fs/Makefile
@@ -105,6 +105,7 @@ obj-$(CONFIG_QNX4FS_FS) += qnx4/
obj-$(CONFIG_AUTOFS4_FS) += autofs4/
obj-$(CONFIG_ADFS_FS) += adfs/
obj-$(CONFIG_FUSE_FS) += fuse/
+obj-$(CONFIG_OVERLAYFS_FS) += overlayfs/
obj-$(CONFIG_UDF_FS) += udf/
obj-$(CONFIG_SUN_OPENPROMFS) += openpromfs/
obj-$(CONFIG_OMFS_FS) += omfs/
--- a/fs/ecryptfs/main.c
+++ b/fs/ecryptfs/main.c
@@ -544,6 +544,13 @@ static struct dentry *ecryptfs_mount(str
s->s_maxbytes = path.dentry->d_sb->s_maxbytes;
s->s_blocksize = path.dentry->d_sb->s_blocksize;
s->s_magic = ECRYPTFS_SUPER_MAGIC;
+ s->s_stack_depth = path.dentry->d_sb->s_stack_depth + 1;
+
+ rc = -EINVAL;
+ if (s->s_stack_depth > FILESYSTEM_MAX_STACK_DEPTH) {
+ printk(KERN_ERR "eCryptfs: maximum fs stacking depth exceeded\n");
+ goto out_free;
+ }
inode = ecryptfs_get_inode(path.dentry->d_inode, s);
rc = PTR_ERR(inode);
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1492,6 +1492,23 @@ void drop_collected_mounts(struct vfsmou
release_mounts(&umount_list);
}
+struct vfsmount *clone_private_mount(struct path *path)
+{
+ struct vfsmount *mnt;
+
+ if (IS_MNT_UNBINDABLE(path->mnt))
+ return ERR_PTR(-EINVAL);
+
+ down_read(&namespace_sem);
+ mnt = clone_mnt(path->mnt, path->dentry, CL_PRIVATE);
+ up_read(&namespace_sem);
+ if (!mnt)
+ return ERR_PTR(-ENOMEM);
+
+ return mnt;
+}
+EXPORT_SYMBOL_GPL(clone_private_mount);
+
int iterate_mounts(int (*f)(struct vfsmount *, void *), void *arg,
struct vfsmount *root)
{
--- a/fs/open.c --- a/fs/open.c
+++ b/fs/open.c +++ b/fs/open.c
@@ -666,8 +666,7 @@ static inline int __get_file_write_acces @@ -666,8 +666,7 @@ static inline int __get_file_write_acces
@ -154,92 +434,6 @@
static void __put_unused_fd(struct files_struct *files, unsigned int fd) static void __put_unused_fd(struct files_struct *files, unsigned int fd)
{ {
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1603,6 +1603,7 @@ struct inode_operations {
void (*truncate_range)(struct inode *, loff_t, loff_t);
int (*fiemap)(struct inode *, struct fiemap_extent_info *, u64 start,
u64 len);
+ struct file *(*open)(struct dentry *, int flags, const struct cred *);
} ____cacheline_aligned;
struct seq_file;
@@ -1998,6 +1999,7 @@ extern long do_sys_open(int dfd, const c
extern struct file *filp_open(const char *, int, int);
extern struct file *file_open_root(struct dentry *, struct vfsmount *,
const char *, int);
+extern struct file *vfs_open(struct path *, int flags, const struct cred *);
extern struct file * dentry_open(struct dentry *, struct vfsmount *, int,
const struct cred *);
extern int filp_close(struct file *, fl_owner_t id);
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -1300,6 +1300,7 @@ long do_splice_direct(struct file *in, l
return ret;
}
+EXPORT_SYMBOL(do_splice_direct);
static int splice_pipe_to_pipe(struct pipe_inode_info *ipipe,
struct pipe_inode_info *opipe,
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1492,6 +1492,23 @@ void drop_collected_mounts(struct vfsmou
release_mounts(&umount_list);
}
+struct vfsmount *clone_private_mount(struct path *path)
+{
+ struct vfsmount *mnt;
+
+ if (IS_MNT_UNBINDABLE(path->mnt))
+ return ERR_PTR(-EINVAL);
+
+ down_read(&namespace_sem);
+ mnt = clone_mnt(path->mnt, path->dentry, CL_PRIVATE);
+ up_read(&namespace_sem);
+ if (!mnt)
+ return ERR_PTR(-ENOMEM);
+
+ return mnt;
+}
+EXPORT_SYMBOL_GPL(clone_private_mount);
+
int iterate_mounts(int (*f)(struct vfsmount *, void *), void *arg,
struct vfsmount *root)
{
--- a/include/linux/mount.h
+++ b/include/linux/mount.h
@@ -100,6 +100,9 @@ extern void mnt_pin(struct vfsmount *mnt
extern void mnt_unpin(struct vfsmount *mnt);
extern int __mnt_is_readonly(struct vfsmount *mnt);
+struct path;
+extern struct vfsmount *clone_private_mount(struct path *path);
+
extern struct vfsmount *do_kern_mount(const char *fstype, int flags,
const char *name, void *data);
--- a/fs/Kconfig
+++ b/fs/Kconfig
@@ -63,6 +63,7 @@ source "fs/quota/Kconfig"
source "fs/autofs4/Kconfig"
source "fs/fuse/Kconfig"
+source "fs/overlayfs/Kconfig"
config CUSE
tristate "Character device in Userspace support"
--- a/fs/Makefile
+++ b/fs/Makefile
@@ -105,6 +105,7 @@ obj-$(CONFIG_QNX4FS_FS) += qnx4/
obj-$(CONFIG_AUTOFS4_FS) += autofs4/
obj-$(CONFIG_ADFS_FS) += adfs/
obj-$(CONFIG_FUSE_FS) += fuse/
+obj-$(CONFIG_OVERLAYFS_FS) += overlayfs/
obj-$(CONFIG_UDF_FS) += udf/
obj-$(CONFIG_SUN_OPENPROMFS) += openpromfs/
obj-$(CONFIG_OMFS_FS) += omfs/
--- /dev/null --- /dev/null
+++ b/fs/overlayfs/Kconfig +++ b/fs/overlayfs/Kconfig
@@ -0,0 +1,4 @@ @@ -0,0 +1,4 @@
@ -645,7 +839,7 @@
+} +}
--- /dev/null --- /dev/null
+++ b/fs/overlayfs/dir.c +++ b/fs/overlayfs/dir.c
@@ -0,0 +1,607 @@ @@ -0,0 +1,596 @@
+/* +/*
+ * + *
+ * Copyright (C) 2011 Novell Inc. + * Copyright (C) 2011 Novell Inc.
@ -663,17 +857,6 @@
+ +
+static const char *ovl_whiteout_symlink = "(overlay-whiteout)"; +static const char *ovl_whiteout_symlink = "(overlay-whiteout)";
+ +
+static struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
+ struct nameidata *nd)
+{
+ int err = ovl_do_lookup(dentry);
+
+ if (err)
+ return ERR_PTR(err);
+
+ return NULL;
+}
+
+static int ovl_whiteout(struct dentry *upperdir, struct dentry *dentry) +static int ovl_whiteout(struct dentry *upperdir, struct dentry *dentry)
+{ +{
+ int err; + int err;
@ -1255,7 +1438,7 @@
+}; +};
--- /dev/null --- /dev/null
+++ b/fs/overlayfs/inode.c +++ b/fs/overlayfs/inode.c
@@ -0,0 +1,375 @@ @@ -0,0 +1,384 @@
+/* +/*
+ * + *
+ * Copyright (C) 2011 Novell Inc. + * Copyright (C) 2011 Novell Inc.
@ -1348,9 +1531,18 @@
+ /* + /*
+ * Writes will always be redirected to upper layer, so + * Writes will always be redirected to upper layer, so
+ * ignore lower layer being read-only. + * ignore lower layer being read-only.
+ *
+ * If the overlay itself is read-only then proceed
+ * with the permission check, don't return EROFS.
+ * This will only happen if this is the lower layer of
+ * another overlayfs.
+ *
+ * If upper fs becomes read-only after the overlay was
+ * constructed return EROFS to prevent modification of
+ * upper layer.
+ */ + */
+ err = -EROFS; + err = -EROFS;
+ if (is_upper && IS_RDONLY(realinode) && + if (is_upper && !IS_RDONLY(inode) && IS_RDONLY(realinode) &&
+ (S_ISREG(mode) || S_ISDIR(mode) || S_ISLNK(mode))) + (S_ISREG(mode) || S_ISDIR(mode) || S_ISLNK(mode)))
+ goto out_dput; + goto out_dput;
+ +
@ -1633,7 +1825,7 @@
+} +}
--- /dev/null --- /dev/null
+++ b/fs/overlayfs/overlayfs.h +++ b/fs/overlayfs/overlayfs.h
@@ -0,0 +1,62 @@ @@ -0,0 +1,63 @@
+/* +/*
+ * + *
+ * Copyright (C) 2011 Novell Inc. + * Copyright (C) 2011 Novell Inc.
@ -1669,7 +1861,8 @@
+void ovl_dentry_set_opaque(struct dentry *dentry, bool opaque); +void ovl_dentry_set_opaque(struct dentry *dentry, bool opaque);
+bool ovl_is_whiteout(struct dentry *dentry); +bool ovl_is_whiteout(struct dentry *dentry);
+void ovl_dentry_update(struct dentry *dentry, struct dentry *upperdentry); +void ovl_dentry_update(struct dentry *dentry, struct dentry *upperdentry);
+int ovl_do_lookup(struct dentry *dentry); +struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
+ struct nameidata *nd);
+ +
+struct dentry *ovl_upper_create(struct dentry *upperdir, struct dentry *dentry, +struct dentry *ovl_upper_create(struct dentry *upperdir, struct dentry *dentry,
+ struct kstat *stat, const char *link); + struct kstat *stat, const char *link);
@ -1866,8 +2059,8 @@
+ return ovl_cache_entry_add_rb(rdd, name, namelen, ino, d_type); + return ovl_cache_entry_add_rb(rdd, name, namelen, ino, d_type);
+} +}
+ +
+static int ovl_dir_read(struct path *realpath, struct ovl_readdir_data *rdd, +static inline int ovl_dir_read(struct path *realpath,
+ filldir_t filler) + struct ovl_readdir_data *rdd, filldir_t filler)
+{ +{
+ struct file *realfile; + struct file *realfile;
+ int err; + int err;
@ -1947,7 +2140,7 @@
+ return 0; + return 0;
+} +}
+ +
+static int ovl_dir_read_merged(struct path *upperpath, struct path *lowerpath, +static inline int ovl_dir_read_merged(struct path *upperpath, struct path *lowerpath,
+ struct ovl_readdir_data *rdd) + struct ovl_readdir_data *rdd)
+{ +{
+ int err; + int err;
@ -2259,7 +2452,7 @@
+} +}
--- /dev/null --- /dev/null
+++ b/fs/overlayfs/super.c +++ b/fs/overlayfs/super.c
@@ -0,0 +1,625 @@ @@ -0,0 +1,656 @@
+/* +/*
+ * + *
+ * Copyright (C) 2011 Novell Inc. + * Copyright (C) 2011 Novell Inc.
@ -2510,7 +2703,7 @@
+ return kzalloc(sizeof(struct ovl_entry), GFP_KERNEL); + return kzalloc(sizeof(struct ovl_entry), GFP_KERNEL);
+} +}
+ +
+static struct dentry *ovl_lookup_real(struct dentry *dir, struct qstr *name) +static inline struct dentry *ovl_lookup_real(struct dentry *dir, struct qstr *name)
+{ +{
+ struct dentry *dentry; + struct dentry *dentry;
+ +
@ -2528,7 +2721,7 @@
+ return dentry; + return dentry;
+} +}
+ +
+int ovl_do_lookup(struct dentry *dentry) +static int ovl_do_lookup(struct dentry *dentry)
+{ +{
+ struct ovl_entry *oe; + struct ovl_entry *oe;
+ struct dentry *upperdir; + struct dentry *upperdir;
@ -2625,6 +2818,17 @@
+ return err; + return err;
+} +}
+ +
+struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
+ struct nameidata *nd)
+{
+ int err = ovl_do_lookup(dentry);
+
+ if (err)
+ return ERR_PTR(err);
+
+ return NULL;
+}
+
+static void ovl_put_super(struct super_block *sb) +static void ovl_put_super(struct super_block *sb)
+{ +{
+ struct ovl_fs *ufs = sb->s_fs_info; + struct ovl_fs *ufs = sb->s_fs_info;
@ -2796,6 +3000,16 @@
+ !S_ISDIR(lowerpath.dentry->d_inode->i_mode)) + !S_ISDIR(lowerpath.dentry->d_inode->i_mode))
+ goto out_put_lowerpath; + goto out_put_lowerpath;
+ +
+ sb->s_stack_depth = max(upperpath.mnt->mnt_sb->s_stack_depth,
+ lowerpath.mnt->mnt_sb->s_stack_depth) + 1;
+
+ err = -EINVAL;
+ if (sb->s_stack_depth > FILESYSTEM_MAX_STACK_DEPTH) {
+ printk(KERN_ERR "overlayfs: maximum fs stacking depth exceeded\n");
+ goto out_put_lowerpath;
+ }
+
+
+ ufs->upper_mnt = clone_private_mount(&upperpath); + ufs->upper_mnt = clone_private_mount(&upperpath);
+ err = PTR_ERR(ufs->upper_mnt); + err = PTR_ERR(ufs->upper_mnt);
+ if (IS_ERR(ufs->upper_mnt)) { + if (IS_ERR(ufs->upper_mnt)) {
@ -2810,6 +3024,16 @@
+ goto out_put_upper_mnt; + goto out_put_upper_mnt;
+ } + }
+ +
+ /*
+ * Make lower_mnt R/O. That way fchmod/fchown on lower file
+ * will fail instead of modifying lower fs.
+ */
+ ufs->lower_mnt->mnt_flags |= MNT_READONLY;
+
+ /* If the upper fs is r/o, we mark overlayfs r/o too */
+ if (ufs->upper_mnt->mnt_sb->s_flags & MS_RDONLY)
+ sb->s_flags |= MS_RDONLY;
+
+ if (!(sb->s_flags & MS_RDONLY)) { + if (!(sb->s_flags & MS_RDONLY)) {
+ err = mnt_want_write(ufs->upper_mnt); + err = mnt_want_write(ufs->upper_mnt);
+ if (err) + if (err)
@ -2885,189 +3109,68 @@
+ +
+module_init(ovl_init); +module_init(ovl_init);
+module_exit(ovl_exit); +module_exit(ovl_exit);
--- /dev/null --- a/fs/splice.c
+++ b/Documentation/filesystems/overlayfs.txt +++ b/fs/splice.c
@@ -0,0 +1,167 @@ @@ -1300,6 +1300,7 @@ long do_splice_direct(struct file *in, l
+Written by: Neil Brown <neilb@suse.de>
+
+Overlay Filesystem
+==================
+
+This document describes a prototype for a new approach to providing
+overlay-filesystem functionality in Linux (sometimes referred to as
+union-filesystems). An overlay-filesystem tries to present a
+filesystem which is the result over overlaying one filesystem on top
+of the other.
+
+The result will inevitably fail to look exactly like a normal
+filesystem for various technical reasons. The expectation is that
+many use cases will be able to ignore these differences.
+
+This approach is 'hybrid' because the objects that appear in the
+filesystem do not all appear to belong to that filesystem. In many
+cases an object accessed in the union will be indistinguishable
+from accessing the corresponding object from the original filesystem.
+This is most obvious from the 'st_dev' field returned by stat(2).
+
+While directories will report an st_dev from the overlay-filesystem,
+all non-directory objects will report an st_dev from the lower or
+upper filesystem that is providing the object. Similarly st_ino will
+only be unique when combined with st_dev, and both of these can change
+over the lifetime of a non-directory object. Many applications and
+tools ignore these values and will not be affected.
+
+Upper and Lower
+---------------
+
+An overlay filesystem combines two filesystems - an 'upper' filesystem
+and a 'lower' filesystem. When a name exists in both filesystems, the
+object in the 'upper' filesystem is visible while the object in the
+'lower' filesystem is either hidden or, in the case of directories,
+merged with the 'upper' object.
+
+It would be more correct to refer to an upper and lower 'directory
+tree' rather than 'filesystem' as it is quite possible for both
+directory trees to be in the same filesystem and there is no
+requirement that the root of a filesystem be given for either upper or
+lower.
+
+The lower filesystem can be any filesystem supported by Linux and does
+not need to be writable. The lower filesystem can even be another
+overlayfs. The upper filesystem will normally be writable and if it
+is it must support the creation of trusted.* extended attributes, and
+must provide valid d_type in readdir responses, at least for symbolic
+links - so NFS is not suitable.
+
+A read-only overlay of two read-only filesystems may use any
+filesystem type.
+
+Directories
+-----------
+
+Overlaying mainly involved directories. If a given name appears in both
+upper and lower filesystems and refers to a non-directory in either,
+then the lower object is hidden - the name refers only to the upper
+object.
+
+Where both upper and lower objects are directories, a merged directory
+is formed.
+
+At mount time, the two directories given as mount options are combined
+into a merged directory:
+
+ mount -t overlayfs overlayfs -olowerdir=/lower,upperdir=/upper /overlay
+
+Then whenever a lookup is requested in such a merged directory, the
+lookup is performed in each actual directory and the combined result
+is cached in the dentry belonging to the overlay filesystem. If both
+actual lookups find directories, both are stored and a merged
+directory is created, otherwise only one is stored: the upper if it
+exists, else the lower.
+
+Only the lists of names from directories are merged. Other content
+such as metadata and extended attributes are reported for the upper
+directory only. These attributes of the lower directory are hidden.
+
+whiteouts and opaque directories
+--------------------------------
+
+In order to support rm and rmdir without changing the lower
+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).
+
+The overlay filesystem uses extended attributes with a
+"trusted.overlay." prefix to record these details.
+
+A whiteout is created as a symbolic link with target
+"(overlay-whiteout)" and with xattr "trusted.overlay.whiteout" set to "y".
+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.
+
+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.
+
+readdir
+-------
+
+When a 'readdir' request is made on a merged directory, the upper and
+lower directories are each read and the name lists merged in the
+obvious way (upper is read first, then lower - entries that already
+exist are not re-added). This merged name list is cached in the
+'struct file' and so remains as long as the file is kept open. If the
+directory is opened and read by two processes at the same time, they
+will each have separate caches. A seekdir to the start of the
+directory (offset 0) followed by a readdir will cause the cache to be
+discarded and rebuilt.
+
+This means that changes to the merged directory do not appear while a
+directory is being read. This is unlikely to be noticed by many
+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
+ - seek to the remembered offset
+
+there may be little correlation between the old and new locations in
+the list of filenames, particularly if anything has changed in the
+directory.
+
+Readdir on directories that are not merged is simply handled by the
+underlying directory (upper or lower).
+
+
+Non-directories
+---------------
+
+Objects that are not directories (files, symlinks, device-special
+files etc.) are presented either from the upper or lower filesystem as
+appropriate. When a file in the lower filesystem is accessed in a way
+the requires write-access, such as opening for write access, changing
+some metadata etc., the file is first copied from the lower filesystem
+to the upper filesystem (copy_up). Note that creating a hard-link
+also requires copy_up, though of course creation of a symlink does
+not.
+
+The copy_up process first makes sure that the containing directory
+exists in the upper filesystem - creating it and any parents as
+necessary. It then creates the object with the same metadata (owner,
+mode, mtime, symlink-target etc.) and then if the object is a file, the
+data is copied from the lower to the upper filesystem. Finally any
+extended attributes are copied up.
+
+Once the copy_up is complete, the overlay filesystem simply
+provides direct access to the newly created file in the upper
+filesystem - future operations on the file are barely noticed by the
+overlay filesystem (though an operation on the name of the file such as
+rename or unlink will of course be noticed and handled).
+
+Changes to underlying filesystems
+---------------------------------
+
+Offline changes, when the overlay is not mounted, are allowed to either
+the upper or the lower trees.
+
+Changes to the underlying filesystems while part of a mounted overlay
+filesystem are not allowed. This is not yet enforced, but will be in
+the future.
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -4727,6 +4727,13 @@ F: drivers/scsi/osd/
F: include/scsi/osd_*
F: fs/exofs/
+OVERLAYFS FILESYSTEM return ret;
+M: Miklos Szeredi <miklos@szeredi.hu> }
+L: linux-fsdevel@vger.kernel.org +EXPORT_SYMBOL(do_splice_direct);
+S: Supported
+F: fs/overlayfs/* static int splice_pipe_to_pipe(struct pipe_inode_info *ipipe,
+F: Documentation/filesystems/overlayfs.txt struct pipe_inode_info *opipe,
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -480,6 +480,12 @@ struct iattr {
*/
#include <linux/quota.h>
+/*
+ * Maximum number of layers of fs stack. Needs to be limited to
+ * prevent kernel stack overflow
+ */
+#define FILESYSTEM_MAX_STACK_DEPTH 2
+ +
P54 WIRELESS DRIVER /**
M: Christian Lamparter <chunkeey@googlemail.com> * enum positive_aop_returns - aop return codes with specific semantics
L: linux-wireless@vger.kernel.org *
@@ -1438,6 +1444,11 @@ struct super_block {
* Saved pool identifier for cleancache (-1 means none)
*/
int cleancache_poolid;
+
+ /*
+ * Indicates how deep in a filesystem stack this SB is
+ */
+ int s_stack_depth;
};
extern struct timespec current_fs_time(struct super_block *sb);
@@ -1603,6 +1614,7 @@ struct inode_operations {
void (*truncate_range)(struct inode *, loff_t, loff_t);
int (*fiemap)(struct inode *, struct fiemap_extent_info *, u64 start,
u64 len);
+ struct file *(*open)(struct dentry *, int flags, const struct cred *);
} ____cacheline_aligned;
struct seq_file;
@@ -1998,6 +2010,7 @@ extern long do_sys_open(int dfd, const c
extern struct file *filp_open(const char *, int, int);
extern struct file *file_open_root(struct dentry *, struct vfsmount *,
const char *, int);
+extern struct file *vfs_open(struct path *, int flags, const struct cred *);
extern struct file * dentry_open(struct dentry *, struct vfsmount *, int,
const struct cred *);
extern int filp_close(struct file *, fl_owner_t id);
--- a/include/linux/mount.h
+++ b/include/linux/mount.h
@@ -100,6 +100,9 @@ extern void mnt_pin(struct vfsmount *mnt
extern void mnt_unpin(struct vfsmount *mnt);
extern int __mnt_is_readonly(struct vfsmount *mnt);
+struct path;
+extern struct vfsmount *clone_private_mount(struct path *path);
+
extern struct vfsmount *do_kern_mount(const char *fstype, int flags,
const char *name, void *data);