Module Name: src
Committed By: riastradh
Date: Mon May 22 14:58:22 UTC 2023
Modified Files:
src/sys/kern: subr_autoconf.c
src/sys/sys: device.h
Log Message:
autoconf(9): New functions for referenced attach/detach.
New functions:
- config_found_acquire(dev, aux, print, cfargs)
- config_attach_acquire(parent, cf, aux, print, cfargs)
- config_attach_pseudo_acquire(cf, aux)
- config_detach_release(dev, flags)
- device_acquire(dev)
The config_*_acquire functions are like the non-acquire versions, but
they return a referenced device_t, which is guaranteed to be safe to
use until released. The device's detach function may run while it is
referenced, but the device_t will not be freed and the parent's
.ca_childdetached routine will not be called.
=> config_attach_pseudo_acquire additionally lets you pass an aux
argument to the device's .ca_attach routine, unlike
config_attach_pseudo which always passes NULL.
=> Eventually, config_found, config_attach, and config_attach_pseudo
should be made to return void, because use of the device_t they
return is unsafe without the kernel lock and difficult to use
safely even with the kernel lock or in a UP system. For now,
they require the caller to hold the kernel lock, while
config_*_acquire do not.
config_detach_release is like device_release and then config_detach,
but avoids the race inherent with that sequence.
=> Eventually, config_detach should be eliminated, because getting at
the device_t it needs is unsafe without the kernel lock and
difficult to use safely even with the kernel lock or in a UP
system. For now, it requires the caller to hold the kernel lock,
while config_detach_release does not.
device_acquire acquires a reference to a device. It never fails and
can be used in thread context (but not interrupt context, hard or
soft). Caller is responsible for ensuring that the device_t cannot
be freed; in other words, the device_t must be made unavailable to
any device_acquire callers before the .ca_detach function returns.
Typically device_acquire will be used in a read section (mutex,
rwlock, pserialize, &c.) in a data structure lookup, with
corresponding logic in the .ca_detach function to remove the device
from the data structure and wait for all read sections to complete.
Proposed on tech-kern:
https://mail-index.netbsd.org/tech-kern/2023/05/10/msg028889.html
To generate a diff of this commit:
cvs rdiff -u -r1.310 -r1.311 src/sys/kern/subr_autoconf.c
cvs rdiff -u -r1.185 -r1.186 src/sys/sys/device.h
Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.
