• Tejun Heo's avatar
    sysfs, kernfs: introduce kernfs_ops · f6acf8bb
    Tejun Heo authored
    
    
    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: default avatarTejun Heo <tj@kernel.org>
    Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
    f6acf8bb