Factor out knote detach operations

[markj]

Summary

All but two knote_drop() calls are preceeded by:

if ((kn->kn_status & KN_DETACHED) != 0)
	kn->kn_fop->f_detach(kn);

One of them is the case where f_attach returns an error. In this case we
free the knote without detaching it, so the attach routine is not
allowed to return an error after adding the knote to a knlist.

The other case is knlist_cleardel(), which manually dequeues the knote
(and sets KN_DETACHED) by calling knlist_remove_kq() immediately before
calling knote_drop().

Therefore, move the detach operation into knote_drop().

[kib]

I like the change.

Myself, I would go even further, e.g. renaming knote_drop() to knote_drop_detached(), and using it in two places which you enumerated in the explanation. knote_drop() would assert KN_DETACHED and called f_detach() unconditionally.

[markj]

In D9015#186078, @kib wrote:

I like the change.

Myself, I would go even further, e.g. renaming knote_drop() to knote_drop_detached(), and using it in two places which you enumerated in the explanation. knote_drop() would assert KN_DETACHED and called f_detach() unconditionally.

Thanks, will do.