ovl: multi-layer readdir

If multiple lower layers exist, merge them as well in readdir according to
the same rules as merging upper with lower. I.e. take whiteouts and opaque
direct

ovl: multi-layer readdir

If multiple lower layers exist, merge them as well in readdir according to
the same rules as merging upper with lower. I.e. take whiteouts and opaque
directories into account on all but the lowers layer.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>

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ovl: helper to iterate layers

Add helper to iterate through all the layers, starting from the upper layer
(if exists) and continuing down through the lower layers.

Signed-off-by

ovl: helper to iterate layers

Add helper to iterate through all the layers, starting from the upper layer
(if exists) and continuing down through the lower layers.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>

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ovl: add mutli-layer infrastructure

Add multiple lower layers to 'struct ovl_fs' and 'struct ovl_entry'.

ovl_entry will have an array of paths, instead of just the dentry. This

ovl: add mutli-layer infrastructure

Add multiple lower layers to 'struct ovl_fs' and 'struct ovl_entry'.

ovl_entry will have an array of paths, instead of just the dentry. This
allows a compact array containing just the layers which exist at current
point in the tree (which is expected to be a small number for the majority
of dentries).

The number of layers is not limited by this infrastructure.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>

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ovl: make path-type a bitmap

OVL_PATH_PURE_UPPER -> __OVL_PATH_UPPER | __OVL_PATH_PURE
OVL_PATH_UPPER -> __OVL_PATH_UPPER
OVL_PATH_MERGE -> __OVL_PATH_UPPER | __OVL_PATH_ME

ovl: make path-type a bitmap

OVL_PATH_PURE_UPPER -> __OVL_PATH_UPPER | __OVL_PATH_PURE
OVL_PATH_UPPER -> __OVL_PATH_UPPER
OVL_PATH_MERGE -> __OVL_PATH_UPPER | __OVL_PATH_MERGE
OVL_PATH_LOWER -> 0

Multiple R/O layers will allow __OVL_PATH_MERGE without __OVL_PATH_UPPER.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>

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ovl: use lockless_dereference() for upperdentry

Don't open code lockless_dereference() in ovl_upperdentry_dereference().

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>

ovl: allow filenames with comma

Allow option separator (comma) to be escaped with backslash.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>

ovl: rename filesystem type to "overlay"

Some distributions carry an "old" format of overlayfs while mainline has a
"new" format.

The distros will possibly want to keep the old

ovl: rename filesystem type to "overlay"

Some distributions carry an "old" format of overlayfs while mainline has a
"new" format.

The distros will possibly want to keep the old overlayfs alongside the new
for compatibility reasons.

To make it possible to differentiate the two versions change the name of
the new one from "overlayfs" to "overlay".

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Reported-by: Serge Hallyn <serge.hallyn@ubuntu.com>
Cc: Andy Whitcroft <apw@canonical.com>

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fs: limit filesystem stacking depth

Add a simple read-only counter to super_block that indicates how deep this
is in the stack of filesystems. Previously ecryptfs was the only stackable

fs: limit filesystem stacking depth

Add a simple read-only counter to super_block that indicates how deep this
is in the stack of filesystems. Previously ecryptfs was the only stackable
filesystem and it explicitly disallowed multiple layers of itself.

Overlayfs, however, can be stacked recursively and also may be stacked
on top of ecryptfs or vice versa.

To limit the kernel stack usage we must limit the depth of the
filesystem stack. Initially the limit is set to 2.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>

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overlayfs: implement show_options

This is useful because of the stacking nature of overlayfs. Users like to
find out (via /proc/mounts) which lower/upper directory were used at mount

overlayfs: implement show_options

This is useful because of the stacking nature of overlayfs. Users like to
find out (via /proc/mounts) which lower/upper directory were used at mount
time.

AV: even failing ovl_parse_opt() could've done some kstrdup()
AV: failure of ovl_alloc_entry() should end up with ENOMEM, not EINVAL

Signed-off-by: Erez Zadok <ezk@cs.sunysb.edu>
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>

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overlayfs: add statfs support

Add support for statfs to the overlayfs filesystem. As the upper layer
is the target of all write operations assume that the space in that
filesystem i

overlayfs: add statfs support

Add support for statfs to the overlayfs filesystem. As the upper layer
is the target of all write operations assume that the space in that
filesystem is the space in the overlayfs. There will be some inaccuracy as
overwriting a file will copy it up and consume space we were not expecting,
but it is better than nothing.

Use the upper layer dentry and mount from the overlayfs root inode,
passing the statfs call to that filesystem.

Signed-off-by: Andy Whitcroft <apw@canonical.com>
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>

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overlay filesystem

Overlayfs allows one, usually read-write, directory tree to be
overlaid onto another, read-only directory tree. All modifications
go to the upper, writable layer.

overlay filesystem

Overlayfs allows one, usually read-write, directory tree to be
overlaid onto another, read-only directory tree. All modifications
go to the upper, writable layer.

This type of mechanism is most often used for live CDs but there's a
wide variety of other uses.

The implementation differs from other "union filesystem"
implementations in that after a file is opened all operations go
directly to the underlying, lower or upper, filesystems. This
simplifies the implementation and allows native performance in these
cases.

The dentry tree is duplicated from the underlying filesystems, this
enables fast cached lookups without adding special support into the
VFS. This uses slightly more memory than union mounts, but dentries
are relatively small.

Currently inodes are duplicated as well, but it is a possible
optimization to share inodes for non-directories.

Opening non directories results in the open forwarded to the
underlying filesystem. This makes the behavior very similar to union
mounts (with the same limitations vs. fchmod/fchown on O_RDONLY file
descriptors).

Usage:

mount -t overlayfs overlayfs -olowerdir=/lower,upperdir=/upper/upper,workdir=/upper/work /overlay

The following cotributions have been folded into this patch:

Neil Brown <neilb@suse.de>:
- minimal remount support
- use correct seek function for directories
- initialise is_real before use
- rename ovl_fill_cache to ovl_dir_read

Felix Fietkau <nbd@openwrt.org>:
- fix a deadlock in ovl_dir_read_merged
- fix a deadlock in ovl_remove_whiteouts

Erez Zadok <ezk@fsl.cs.sunysb.edu>
- fix cleanup after WARN_ON

Sedat Dilek <sedat.dilek@googlemail.com>
- fix up permission to confirm to new API

Robin Dong <hao.bigrat@gmail.com>
- fix possible leak in ovl_new_inode
- create new inode in ovl_link

Andy Whitcroft <apw@canonical.com>
- switch to __inode_permission()
- copy up i_uid/i_gid from the underlying inode

AV:
- ovl_copy_up_locked() - dput(ERR_PTR(...)) on two failure exits
- ovl_clear_empty() - one failure exit forgetting to do unlock_rename(),
lack of check for udir being the parent of upper, dropping and regaining
the lock on udir (which would require _another_ check for parent being
right).
- bogus d_drop() in copyup and rename [fix from your mail]
- copyup/remove and copyup/rename races [fix from your mail]
- ovl_dir_fsync() leaving ERR_PTR() in ->realfile
- ovl_entry_free() is pointless - it's just a kfree_rcu()
- fold ovl_do_lookup() into ovl_lookup()
- manually assigning ->d_op is wrong. Just use ->s_d_op.
[patches picked from Miklos]:
* copyup/remove and copyup/rename races
* bogus d_drop() in copyup and rename

Also thanks to the following people for testing and reporting bugs:

Jordi Pujol <jordipujolp@gmail.com>
Andy Whitcroft <apw@canonical.com>
Michal Suchanek <hramrach@centrum.cz>
Felix Fietkau <nbd@openwrt.org>
Erez Zadok <ezk@fsl.cs.sunysb.edu>
Randy Dunlap <rdunlap@xenotime.net>

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>

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