We've run into problems with running out of dynamicly assign char
device majors particullarly on automated test systems with
all-yes-configs. Roughly 40 dynamic assignments can be made with such
kernels at this time while space is reserved for only 20.
Currently, the kernel only prints a warning when dynamic allocation
overflows the reserved region. And when this happens drivers that have
fixed assignments can randomly fail depending on the order of
initialization of other drivers. Thus, adding a new char device can cause
unexpected failures in completely unrelated parts of the kernel.
This patch solves the problem by extending dynamic major number
allocations down from 511 once the 234-254 region fills up. Fixed
majors already exist above 255 so the infrastructure to support
high number majors is already in place. The patch reserves an
additional 128 major numbers which should hopefully last us a while.
Kernels that don't require more than 20 dynamic majors assigned (which
is pretty typical) should not be affected by this change.
Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Alan Cox <alan@linux.intel.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Linus Walleij <linus.walleij@linaro.org>
Link: https://lkml.org/lkml/2017/6/4/107
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Vhost-vsock is a software device so there is no probe call that causes
the driver to register its misc char device node. This creates a
chicken and egg problem: userspace applications must open
/dev/vhost-vsock to use the driver but the file doesn't exist until the
kernel module has been loaded.
Use the devname modalias mechanism so that /dev/vhost-vsock is created
at boot. The vhost_vsock kernel module is automatically loaded when the
first application opens /dev/host-vsock.
Note that the "reserved for local use" range in
Documentation/admin-guide/devices.txt is incorrect. The userio driver
already occupies part of that range. I've updated the documentation
accordingly.
Cc: device@lanana.org
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
