Date: Thu, 6 Apr 2000 21:01:39 -0700 (PDT) From: Matthew Dillon <dillon@apollo.backplane.com> To: Jonathan Lemon <jlemon@flugsvamp.com> Cc: Archie Cobbs <archie@whistle.com>, freebsd-arch@freebsd.org Subject: Re: RFC: kqueue API and rough code Message-ID: <200004070401.VAA93492@apollo.backplane.com> References: <200004070107.SAA97591@bubba.whistle.com> <200004070220.TAA92896@apollo.backplane.com> <20000406220454.J80578@prism.flugsvamp.com>
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Hey! (I snap my fingers), I got it!
There is no need to copy anything back and forth from user space to
kernel space!
It's simple, really. How about this API:
qfd = kqueue();
kqueuectl(qfd, filter, fd, struct event *ev);
ev = kevent(qfd, timeout);
or (another way to do kevent):
n = kevent(qfd, struct event **ary, int nmax, struct timeval *timeout);
The key thing here is that the kernel creates its own internal data
structure which has the descriptor, filter operation, and a pointer
to the *USER* event structure. The kernel would not otherwise copy
the user event structure into kernel space nor would it copy it back
to return the event.
Instead when an event occurs the kernel does a copyout of *ONLY* the
kernel data update for the event structure (the 'data') field. What it
returns to user space in the kevent() call is not the event itself,
but a POINTER to the event that the user originally passed it.
If we do this then the user has the ability to extend the
struct event structure to contain whatever the user wants. All the
kernel cares about is the 'data' field.
I would still reserve a bunch of fields for future direct kernel support
for things like automatic function/thread dispatching, but this will
result in a minimally sized in-kernel data structure and no copying back
and forth (except to update the user 'data' field, which the kernel does
in the kevent() syscall).
The user event structure passed to the kernel (the kernel doesn't need
to touch it at all except when populating 'data' when kevent() is
returning events:
struct event {
long data;
void (*dispatch)(struct event *ev);
int reserved[2];
};
The kernel internal event structure (or equivalent):
struct kevent {
int fd;
long data; /* to be copied into the uevent */
short filter;
short flags;
struct event *uevent;
};
-Matt
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