CVS commit: src/sys

["Taylor R Campbell" <riastradh%netbsd.org@localhost>]

Module Name:    src
Committed By:   riastradh
Date:           Mon Mar 28 12:33:50 UTC 2022

Modified Files:
        src/sys/kern: subr_devsw.c
        src/sys/sys: conf.h

Log Message:
driver(9): New devsw members d_cfdriver, d_devtounit.

If set, then bdev_open/cdev_open will use d_devtounit to map the
dev_t to an autoconf instance (e.g., /dev/wd0a -> wd0) and hold a
reference with device_lookup_acquire across the call to d_open.

This guarantees that the autoconf instance cannot be detached while
the devsw's d_open function is trying to open it (and also that the
autoconf instance has finished *_attach before anyone can open it).

Of course, if the underlying hardware has gone away, there will be
I/O errors, but this avoids software synchronization bugs between
open and detach for drivers that opt into it.  It's up to the driver
and bus to figure out how to deal with I/O errors from operations on
hardware that has gone away while the software hasn't finished
notifying everything that it's gone yet.

XXX kernel ABI change to struct bdevsw/cdevsw requires bump


To generate a diff of this commit:
cvs rdiff -u -r1.40 -r1.41 src/sys/kern/subr_devsw.c
cvs rdiff -u -r1.155 -r1.156 src/sys/sys/conf.h

Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.