sysfs, kernfs: introduce kernfs_ops

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: Tejun Heo <tj@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 26 insertions, 0 deletions

diff --git a/include/linux/kernfs.h b/include/linux/kernfs.h
index b923052c29d0..97c6c0f91325 100644
--- a/include/linux/kernfs.h
+++ b/include/linux/kernfs.h
@@ -33,6 +33,32 @@ struct sysfs_open_file {
 	const struct vm_operations_struct *vm_ops;
 };
 
+struct kernfs_ops {
+	/*
+	 * Read is handled by either seq_file or raw_read().
+	 *
+	 * If seq_show() is present, seq_file path is active.  The behavior
+	 * is equivalent to single_open().  @sf->private points to the
+	 * associated sysfs_open_file.
+	 *
+	 * read() is bounced through kernel buffer and a read larger than
+	 * PAGE_SIZE results in partial operation of PAGE_SIZE.
+	 */
+	int (*seq_show)(struct seq_file *sf, void *v);
+
+	ssize_t (*read)(struct sysfs_open_file *of, char *buf, size_t bytes,
+			loff_t off);
+
+	/*
+	 * write() is bounced through kernel buffer and a write larger than
+	 * PAGE_SIZE results in partial operation of PAGE_SIZE.
+	 */
+	ssize_t (*write)(struct sysfs_open_file *of, char *buf, size_t bytes,
+			 loff_t off);
+
+	int (*mmap)(struct sysfs_open_file *of, struct vm_area_struct *vma);
+};
+
 #ifdef CONFIG_SYSFS
 
 struct sysfs_dirent *kernfs_create_dir_ns(struct sysfs_dirent *parent,