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Date: Wed, 24 Jul 1996 20:26:07 +1000
From: Bruce Evans <bde@zeta.org.au>
Message-Id: <199607241026.UAA21158@godzilla.zeta.org.au>
To: CVS-committers@freefall.freebsd.org, cvs-all@freefall.freebsd.org,
        cvs-sys@freefall.freebsd.org, phk@freefall.freebsd.org
Subject: Re: cvs commit:  src/sys/dev/ccd ccd.c src/sys/dev/vn vn.c src/sys/sys conf.h src/sys/i386/isa fd.c mcd.c scd.c wcd.c wd.c wt.c src/sys/i386/isa/matcd matcd.c src/sys/kern kern_conf.c src/sys/scsi cd.c od.c sd.c st.c
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>  Modified:    sys/dev/ccd  ccd.c
>               sys/dev/vn  vn.c
>               sys/i386/isa  fd.c mcd.c scd.c wcd.c wd.c wt.c
>               sys/i386/isa/matcd  matcd.c
>               sys/kern  kern_conf.c
>               sys/scsi  cd.c od.c sd.c st.c
>               sys/sys   conf.h
>  Log:
>  Make a "DWIM" function for adding [bc]devsw entries for bdev drivers.
>  
>  Saves about 280 butes of source per driver, 56 bytes in object size
>  and another 56 bytes moves from data to bss.

This broke wcd, which has bogusly different open and close functions for
cdevs and bdevs.  Compiling LINT gives a nice warning that the cdev open
and close functions are no longer used.

This change interferes with the correct change, which is to nuke the
SYSINIT()s and call bdevsw_add() and cdevsw_add() in the device attach
functions.  These functions should eventually have a different interface
that doesn't involve the driver knowing its own device number.  The main
wastages in the previous interface were the makedevs and the always-NULL
pointers.  Changing [bc]devsw_add() to take args (int major, struct
[bc]devsw *new) would save about the same amount of space as using the
new generic interface for bdev drivers, and more space for cdev-only
drivers.  However, this might break the intended final interface, which
may involve passing back the `old' devsw pointer and a reconstructed
device number.  Changing to bdevsw_add_generic() has already broken it.
However^2, the final interface should involve device descriptors instead
of numbers, and overwriting an in-use device descriptor should be an
error so `old' pointers should be useless (they would always point to a
garbage devsw).  Thus the current interface is not worth preserving.

Bruce