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From: fred@rover.UUCP (Fred Christiansen)
Newsgroups: comp.unix.wizards
Subject: need help porting SysV driver to Berkeley
Message-ID: <487@rover.UUCP>
Date: Fri, 28-Aug-87 15:32:38 EDT
Article-I.D.: rover.487
Posted: Fri Aug 28 15:32:38 1987
Date-Received: Sun, 30-Aug-87 06:32:53 EDT
Reply-To: fred@rover.UUCP (Fred Christiansen)
Organization: Motorola Microcomputer Division, Tempe, Az.
Lines: 24

a co-worker is attempting to port a driver from System V/68 (SysV)
to a Sun (Berkeley).  he brought this question to me, which i can't
answer.  can someone help?

if a user does a read(), like:
	n = read( fd, buf, sizeof( buf ) );
then inside a SysV kernel, u.u_base is the address of `buf', while
u.u_count is `sizeof( buf )'.  after the copyout(), i decrement
u.u_count by the number of bytes copied.  then, by someone between
the driver read return and the read() return, someone subtracts
u.u_count from `sizeof( buf )' so that the return value of read()
is the number of bytes read.

the co-worker has read Sun's device driver writer's guide, but
does not understand (so cannot explain to me) the use of `struct uio'
and `struct iovec'.  under SunOS, read()'s are returning 0.
what needs to get set so the real number of bytes read gets returned.

thanks!
-- 
Fred Christiansen ("Canajun, eh?")     | seismo!noao!mcdsun!nud!fred (ARPA gate)
Motorola Microcomputer Div., Tempe, AZ |       utzoo!mnetor!mot!fred
"The greatest thing a father can do for|              ihnp4!mot!fred
his children is to love their mother." |  hplabs!motsj1!ellygroup ...