Re: connector.c

[Andrew Morton]

Evgeniy Polyakov <johnpol@xxxxxxxxxxx> wrote:
>
> > What happens if we expect a reply to our message but userspace never sends
> > one?  Does the kernel leak memory?  Do other processes hang?
> 
> It is only advice, one may easily skip seq/ack initialization.
> I could remove it totally from the header, but decided to 
> place it to force people to use more reliable protocols over netlink
> by introducing such overhead.

hm.  I don't know what that means.

> > > 	nlh = NLMSG_PUT(skb, 0, msg->seq, NLMSG_DONE, size - sizeof(*nlh));
> > > 
> > > 	data = (struct cn_msg *)NLMSG_DATA(nlh);
> > 
> > Unneeded typecast.
> 
> Is it really an issue?

Well it adds clutter, but more significantly the cast defeats typechecking.
If someone was to change NLMSG_DATA() to return something other than
void*, the compiler wouldn't complain.

> > 
> > Why is spin_lock_bh() being used here?
> 
> skb may be delivered in soft irq context, and may race with sending.
> And actually it can be sent from irq context, like it is done in test
> module.

But spin_lock_bh() in irq context will deadlock if interruptible context is
also doing spin_lock_bh().

> > What's all the above code doing?  What do `a' and `b' mean?  Needs
> > commentary and better-chosen identifiers.
> 
> It searches for idx and val to match requested notification, 
> if "a" is true - idx is found, if b - val is found.

Let me rephrase: please comment the code and choose identifiers in a manner
which makes it clearer what's going on.

> > Please document all functions with comments.  Functions which constitute
> > part of the external API should be commented using the kernel-doc format.
> 
> There is Documentation/connector/connector.txt which describes all
> exported functions and structures.
> Should it be ported to docbook?

connector.txt is pitched at about the right level: an in-kernel and
userspace API description.  It's rather unclear with respect to mesage
directions though - whether the callback is invoked after kernel->user
messages, or for user->kernel or what, for example.  Some clarification
there would help.  

But an API description is a different thing from code commentary which
explains the internal design - the latter should be coupled to the code
itself. 


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