问一个ACL函数的问题

zhangad

在内核目录include/linux/posix_acl.h文件中，有2个函数，代码如下：
看这两个函数时，总是看不太明白是作什么用的。那位高手能解释一下，thx！
static inline void forget_cached_acl(struct inode *inode, int type)
{
struct posix_acl **p = acl_by_type(inode, type);
struct posix_acl *old;
spin_lock(&inode->i_lock);
old = *p;
*p = ACL_NOT_CACHED;
spin_unlock(&inode->i_lock);
if (old != ACL_NOT_CACHED)
posix_acl_release(old);
}

static inline void forget_all_cached_acls(struct inode *inode)
{
struct posix_acl *old_access, *old_default;
spin_lock(&inode->i_lock);
old_access = inode->i_acl;
old_default = inode->i_default_acl;
inode->i_acl = inode->i_default_acl = ACL_NOT_CACHED;
spin_unlock(&inode->i_lock);
if (old_access != ACL_NOT_CACHED)
posix_acl_release(old_access);
if (old_default != ACL_NOT_CACHED)
posix_acl_release(old_default);
}