kernfs_addrm_start kernfs_add_one

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linux内核版本3.14.3

文件/fs/kernfs/dir.c

/**
* kernfs_addrm_start - 为kernfs_node添加/删除准备
* @acxt: 指向要使用的kernfs_addrm_cxt的指针
*
* 该方法在调用方需要添加或删除kernfs_node的时候调用，该方法需要
* kernfs_mutex. @acxt是用来保存和传递内容到其他的addrm(add/remove)方法
*
* LOCKING:
* Kernel thread context (may sleep). kernfs_mutex is locked on
* return.
*/
void kernfs_addrm_start(struct kernfs_addrm_cxt *acxt)
__acquires(kernfs_mutex)
{
memset(acxt, 0, sizeof(*acxt));

mutex_lock(&kernfs_mutex);
}

这里的缩写让我很难办，addrm是(add/rm)，cxt是context，看下面的结构体就可以理解了

文件/fs/kernfs/kernfs-internal.h

/*
* Context structure to be used while adding/removing nodes.看英文更容易明白缩写到底是啥
*/
struct kernfs_addrm_cxt {
struct kernfs_node*removed;
};

文件/fs/kernfs/dir.c

/**
* kernfs_add_one - 无警告添加kernfs_node到parent
* @acxt: 用于add/remove的context
* @kn: 用来添加的kernfs_node
*
* 该调用必须已经初始化过@kn->parent. 如果@kn是一个目录，
* 该方法会增加parent的inode的nlink，并链接到parent的 children list.
*
* 该方法应该在kernfs_addrm_start()和kernfs_addrm_finish()
* 之间调用，并应该和和kernfs_addrm_start()传递相同的@acxt.
*
* LOCKING:
* Determined by kernfs_addrm_start().
*
* RETURNS:
* 成功返回0, 如果给定的entry名称已存在返回-EEXIST
*/
int kernfs_add_one(struct kernfs_addrm_cxt *acxt, struct kernfs_node *kn)
{
  struct kernfs_node *parent = kn->parent;
  bool has_ns = kernfs_ns_enabled(parent);
  struct kernfs_iattrs *ps_iattr;
  int ret;

  if (has_ns != (bool)kn->ns) {
      WARN(1, KERN_WARNING "kernfs: ns %s in '%s' for '%s'\n", has_ns ? "required" : "invalid", parent->name, kn->name);
      return -EINVAL;
  }

  if (kernfs_type(parent) != KERNFS_DIR)
  return -EINVAL;

  if (parent->flags & KERNFS_REMOVED)
  return -ENOENT;

  kn->hash = kernfs_name_hash(kn->name, kn->ns);

  ret = kernfs_link_sibling(kn);
  if (ret)
      return ret;

  /* 更新parent的时间戳*/
  ps_iattr = parent->iattr;
  if (ps_iattr) {
      struct iattr *ps_iattrs = &ps_iattr->ia_iattr;
      ps_iattrs->ia_ctime = ps_iattrs->ia_mtime = CURRENT_TIME;
  }

  /* Mark the entry added into directory tree */
  kn->flags &= ~KERNFS_REMOVED;

  return 0;
}

/**
* kernfs_name_hash
* @name: 转hash的以Null('\0')结尾的字符串
* @ns: 转hash的命名空间tag
*
* Returns 31 bit hash of ns + name (so it fits in an off_t )
*/
static unsigned int kernfs_name_hash(const char *name, const void *ns)
{
  unsigned long hash = init_name_hash();//#define init_name_hash() 0
  unsigned int len = strlen(name);
  while (len--)
      hash = partial_name_hash(*name++, hash);
  hash = (end_name_hash(hash) ^ hash_ptr((void *)ns, 31));
  hash &= 0x7fffffffU;
  /* Reserve hash numbers 0, 1 and INT_MAX for magic directory entries */
  if (hash < 2)
      hash += 2;
  if (hash >= INT_MAX)
      hash = INT_MAX - 1;
  return hash;
}

文件/include/linux/dcache.h

/* partial hash update function. Assume roughly 4 bits per character */
static inline unsigned long
partial_name_hash(unsigned long c, unsigned long prevhash)
{
return (prevhash + (c << 4) + (c >> 4)) * 11;
}

我想这里就到此为止吧，所谓的kernfs_name_hash无非是把name这个字符串通过一个复杂的计算方法转换为一个unsigned int的数值，据说是为了查找方便，而这个复杂的算法，就先不研究了

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