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    sysfs: restructure add/remove paths and fix inode update · fb6896da
    Tejun Heo 提交于
    The original add/remove code had the following problems.
    
    * parent's timestamps are updated on dentry instantiation.  this is
      incorrect with reclaimable files.
    
    * updating parent's timestamps isn't synchronized.
    
    * parent nlink update assumes the inode is accessible which won't be
      true once directory dentries are made reclaimable.
    
    This patch restructures add/remove paths to resolve the above
    problems.  Add/removal are done in the following steps.
    
    1. sysfs_addrm_start() : acquire locks including sysfs_mutex and other
       resources.
    
    2-a. sysfs_add_one() : add new sd.  linking the new sd into the
         children list is caller's responsibility.
    
    2-b. sysfs_remove_one() : remove a sd.  unlinking the sd from the
         children list is caller's responsibility.
    
    3. sysfs_addrm_finish() : release all resources and clean up.
    
    Steps 2-a and/or 2-b can be repeated multiple times.
    
    Parent's inode is looked up during sysfs_addrm_start().  If available
    (always at the moment), it's pinned and nlink is updated as sd's are
    added and removed.  Timestamps are updated during finish if any sd has
    been added or removed.  If parent's inode is not available during
    start, sysfs_mutex ensures that parent inode is not created till
    add/remove is complete.
    
    All the complexity is contained inside the helper functions.
    Especially, dentry/inode handling is properly hidden from the rest of
    sysfs which now mostly operate on sysfs_dirents.  As an added bonus,
    codes which use these helpers to add and remove sysfs_dirents are now
    more structured and simpler.
    Signed-off-by: NTejun Heo <htejun@gmail.com>
    Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>
    fb6896da
sysfs.h 3.9 KB