Introduce kernfs interface for finding, getting and putting
sysfs_dirents.

* sysfs_find_dirent() is renamed to kernfs_find_ns() and lockdep
  assertion for sysfs_mutex is added.

* sysfs_get_dirent_ns() is renamed to kernfs_find_and_get().

* Macro inline dancing around __sysfs_get/put() are removed and
  kernfs_get/put() are made proper functions implemented in
  fs/sysfs/dir.c.

While the conversions are mostly equivalent, there's one difference -
kernfs_get() doesn't return the input param as its return value.  This
change is intentional.  While passing through the input increases
writability in some areas, it is unnecessary and has been shown to
cause confusion regarding how the last ref is handled.
Signed-off-by: NTejun Heo <tj@kernel.org>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

Currently, sysfs_dirent active_ref lockdep annotation uses
attribute->[s]key as the lockdep key, which forces
kernfs_create_file_ns() to assume that sysfs_dirent->priv is pointing
to a struct attribute which may not be true for non-sysfs users.  This
patch restructures the lockdep annotation such that

* kernfs_ops contains lockdep_key which is used by default for files
  created kernfs_create_file_ns().

* kernfs_create_file_ns_key() is introduced which takes an extra @key
  argument.  The created file will use the specified key for
  active_ref lockdep annotation.  If NULL is specified, lockdep for
  the file is disabled.

* sysfs_add_file_mode_ns() is updated to use
  kernfs_create_file_ns_key() with the appropriate key from the
  attribute or NULL if ignore_lockdep is set.

This makes the lockdep annotation properly contained in kernfs while
allowing sysfs to cleanly keep its current behavior.  This patch
doesn't introduce any behavior differences.
Signed-off-by: NTejun Heo <tj@kernel.org>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

Introduce kernfs interface to wake up poll(2) which takes and returns
sysfs_dirents.

sysfs_notify_dirent() is renamed to kernfs_notify() and sysfs_notify()
is updated so that it doesn't directly grab sysfs_mutex but acquires
the target sysfs_dirents using sysfs_get_dirent().
sysfs_notify_dirent() is reimplemented as a dumb inline wrapper around
kernfs_notify().

This patch doesn't introduce any behavior changes.
Signed-off-by: NTejun Heo <tj@kernel.org>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

kernfs_ops currently only supports single_open() behavior which is
pretty restrictive.  Add optional callbacks ->seq_{start|next|stop}()
which, when implemented, are invoked for seq_file traversal.  This
allows full seq_file functionality for kernfs users.  This currently
doesn't have any user and doesn't change any behavior.

v2: Refreshed on top of the updated "sysfs, kernfs: prepare read path
    for kernfs".
Signed-off-by: NTejun Heo <tj@kernel.org>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

Introduce kernfs interface to create a file which takes and returns
sysfs_dirents.

The actual file creation part is separated out from
sysfs_add_file_mode_ns() into kernfs_create_file_ns().  The former now
only decides the kernfs_ops to use and the file's size and invokes the
latter.

This patch doesn't introduce behavior changes.

v2: Dummy implementation for !CONFIG_SYSFS updated to return -ENOSYS.
Signed-off-by: NTejun Heo <tj@kernel.org>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

We're in the process of separating out core sysfs functionality into
kernfs which will deal with sysfs_dirents directly.  This patch
introduces kernfs_ops which hosts methods kernfs users implement and
updates fs/sysfs/file.c such that sysfs_kf_*() functions populate
kernfs_ops and kernfs_file_*() functions call the matching entries
from kernfs_ops.

kernfs_ops contains the following groups of methods.

* seq_show() - for kernfs files which use seq_file for reads.

* read() - for direct read implementations.  Used iff seq_show() is
  not implemented.

* write() - for writes.

* mmap() - for mmaps.

Notes:

* sysfs_elem_attr->ops is added so that kernfs_ops can be accessed
  from sysfs_dirent.  kernfs_ops() helper is added to verify locking
  and access the field.

* SYSFS_FLAG_HAS_(SEQ_SHOW|MMAP) added.  sd->s_attr->ops is accessible
  only while holding active_ref and there are cases where we want to
  take different actions depending on which ops are implemented.
  These two flags cache whether the two ops are implemented for those.

* kernfs_file_*() no longer test sysfs type but chooses different
  behaviors depending on which methods in kernfs_ops are implemented.
  The conversions are trivial except for the open path.  As
  kernfs_file_open() now decides whether to allow read/write accesses
  depending on the kernfs_ops implemented, the presence of methods in
  kobjs and attribute_bin should be propagated to kernfs_ops.
  sysfs_add_file_mode_ns() is updated so that it propagates presence /
  absence of the callbacks through _empty, _ro, _wo, _rw kernfs_ops.
Signed-off-by: NTejun Heo <tj@kernel.org>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

sysfs_open_file will be used as the primary handle for kernfs methods.
Move its definition from fs/sysfs/file.c to include/linux/kernfs.h and
mark the public and private fields.

This is pure relocation.
Signed-off-by: NTejun Heo <tj@kernel.org>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

Introduce kernfs interface to manipulate a directory which takes and
returns sysfs_dirents.

create_dir() is renamed to kernfs_create_dir_ns() and its argumantes
and return value are updated.  create_dir() usages are replaced with
kernfs_create_dir_ns() and sysfs_create_subdir() usages are replaced
with kernfs_create_dir().  Dup warnings are handled explicitly by
sysfs users of the kernfs interface.

sysfs_enable_ns() is renamed to kernfs_enable_ns().

This patch doesn't introduce any behavior changes.

v2: Dummy implementation for !CONFIG_SYSFS updated to return -ENOSYS.

v3: kernfs_enable_ns() added.

v4: Refreshed on top of "sysfs: drop kobj_ns_type handling, take #2"
    so that this patch removes sysfs_enable_ns().
Signed-off-by: NTejun Heo <tj@kernel.org>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

Introduce kernfs setattr interface - kernfs_setattr().

sysfs_sd_setattr() is renamed to __kernfs_setattr() and
kernfs_setattr() is a simple wrapper around it with sysfs_mutex
locking.  sysfs_chmod_file() is updated to get an explicit ref on
kobj->sd and then invoke kernfs_setattr() so that it doesn't have to
use internal interface.

This patch doesn't introduce any behavior differences.

v2: Dummy implementation for !CONFIG_SYSFS updated to return -ENOSYS.
Signed-off-by: NTejun Heo <tj@kernel.org>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

Introduce kernfs rename interface, krenfs_rename[_ns]().

This is just rename of sysfs_rename().  No functional changes.
Function comment is added to kernfs_rename_ns() and @new_parent_sd is
renamed to @new_parent for consistency with other kernfs interfaces.

v2: Dummy implementation for !CONFIG_SYSFS updated to return -ENOSYS.
Signed-off-by: NTejun Heo <tj@kernel.org>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

Separate out kernfs symlink interface - kernfs_create_link() - which
takes and returns sysfs_dirents, from sysfs_do_create_link_sd().
sysfs_do_create_link_sd() now just determines the parent and target
sysfs_dirents and invokes the new interface and handles dup warning.

This patch doesn't introduce behavior changes.

v2: Dummy implementation for !CONFIG_SYSFS updated to return -ENOSYS.
Signed-off-by: NTejun Heo <tj@kernel.org>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

Introduce kernfs removal interfaces - kernfs_remove() and
kernfs_remove_by_name[_ns]().

These are just renames of sysfs_remove() and sysfs_hash_and_remove().
No functional changes.

v2: Dummy kernfs_remove_by_name_ns() for !CONFIG_SYSFS updated to
    return -ENOSYS instead of 0.
Signed-off-by: NTejun Heo <tj@kernel.org>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

Core sysfs implementation will be separated into kernfs so that it can
be used by other non-kobject users.

This patch creates fs/kernfs/ directory and makes boilerplate changes.
kernfs interface will be directly based on sysfs_dirent and its
forward declaration is moved to include/linux/kernfs.h which is
included from include/linux/sysfs.h.  sysfs core implementation will
be gradually separated out and moved to kernfs.

This patch doesn't introduce any functional changes.

v2: mount.c added.
Signed-off-by: NTejun Heo <tj@kernel.org>
Cc: linux-fsdevel@vger.kernel.org
Cc: Christoph Hellwig <hch@infradead.org>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>