* h.vanberkum@chello.nl (h.vanberkum@chello.nl) wrote:
> Hello everybody,
>
> I've seen a presentation on LSM in a irc channel. I would like to
> know more on hooks and callbacks in the kernel. What's the difference
> between hooks and callbacks?
As Greg mentioned, they are often used interchangeably. One minor
distinction:
The hook is the location in the kernel where code is called from. For
example:
error = security_inode_create(dir, dentry, mode);
This code is called in the kernel's VFS create function. This is the
hook. However, if you look more closely you'll find:
static inline int security_inode_create (struct inode *dir,
struct dentry *dentry,
int mode)
{
return security_ops->inode_create (dir, dentry, mode);
}
The hook calls a function pointer in the security_ops structure. The
code that is executed though this function pointer is set by the
security module when it registers it's security_ops structure. This
code is the callback code.
> What happens if hooks and callbacks are
> not registered?(null pointer?)
For LSM, as Greg said, the framework fills out a default callback for
the null values during registration. Other parts of the kernel will
test for null pointers and use a default if the pointer is null (inline
in the code). The VFS is a fine example of that.
thanks,
-chris
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