Move tty_driver_lookup_tty() and tty_reopen() from tty_init_dev()
into tty_open() (one of the two callers of tty_init_dev()). These
calls are not really required in ptmx_open(), the other caller,
since ptmx_open() would be setting up a new tty.
Changelog[v2]:
- remove the lookup and reopen calls from ptmx_open
- merge with recent changes to ttydev tree
Alan Cox [Mon, 13 Oct 2008 09:42:19 +0000 (10:42 +0100)]
tty: More driver operations
We have the lookup operation abstracted which is nice for pty cleanup but
we really want to abstract the add/remove entries as well so that we can
pull the pty code out of the tty core and create a clear defined interface
for the tty driver table.
Signed-off-by: Alan Cox <alan@redhat.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Alan Cox [Mon, 13 Oct 2008 09:41:42 +0000 (10:41 +0100)]
tty: Remove more special casing and out of place code
Carry on pushing code out of tty_io when it belongs to other drivers. I'm
not 100% happy with some of this and it will be worth revisiting some of the
exports later when the restructuring work is done.
Signed-off-by: Alan Cox <alan@redhat.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Alan Cox [Mon, 13 Oct 2008 09:41:30 +0000 (10:41 +0100)]
tty: shutdown method
Right now there are various drivers that try to use tty->count to know when
they get the final close. Aristeau Rozanski showed while debugging the vt
sysfs race that this isn't entirely safe.
Instead of driver side tricks to work around this introduce a shutdown which
is called when the tty is being destructed. This also means that the shutdown
method is tied into the refcounting.
Use this to rework the console close/sysfs logic.
Remove lots of special case code from the tty core code. The pty code can now
have a shutdown() method that replaces the special case hackery in the tree
free up paths.
Signed-off-by: Alan Cox <alan@redhat.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Alan Cox [Mon, 13 Oct 2008 09:41:16 +0000 (10:41 +0100)]
vt: remove bogus lock dropping
For hysterical raisins the vt layer drops and retakes locks in the write
method. This is a left over from the days when user/kernel data was passed
directly to the tty not pre-buffered.
Signed-off-by: Alan Cox <alan@redhat.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Alan Cox [Mon, 13 Oct 2008 09:41:03 +0000 (10:41 +0100)]
pty: If the administrator creates a device for a ptmx slave we should not error
The open path for ptmx slaves is via the ptmx device. Opening them any
other way is not allowed. Vegard Nossum found that previously this was not
the case and mknod foo c 128 42; cat foo would produce nasty diagnostics
Signed-off-by: Alan Cox <alan@redhat.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Alan Cox [Mon, 13 Oct 2008 09:40:53 +0000 (10:40 +0100)]
tty: Fix abusers of current->sighand->tty
Various people outside the tty layer still stick their noses in behind the
scenes. We need to make sure they also obey the locking and referencing rules.
Signed-off-by: Alan Cox <alan@redhat.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Alan Cox [Mon, 13 Oct 2008 09:40:43 +0000 (10:40 +0100)]
tty: Redo current tty locking
Currently it is sometimes locked by the tty mutex and sometimes by the
sighand lock. The latter is in fact correct and now we can hand back referenced
objects we can fix this up without problems around sleeping functions.
Signed-off-by: Alan Cox <alan@redhat.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Alan Cox [Mon, 13 Oct 2008 09:40:07 +0000 (10:40 +0100)]
stallion: Use krefs
Use tty_port_init and krefs in the stallion drivers to protect us from devices
going away underneath us. As with the other drives some rearranging is done to
pass the tty structure down properly on the user side.
Signed-off-by: Alan Cox <alan@redhat.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Alan Cox [Mon, 13 Oct 2008 09:39:58 +0000 (10:39 +0100)]
tty: kref usage for isicom and moxa
Rather than blindly keep taking krefs we reorder the code in a few places
to pass the tty down to the right place (which is important as from the user
side it is not the case that tty == port->tty in all situations). For the irq
and related paths use the krefs to stop the tty being freed under us.
Signed-off-by: Alan Cox <alan@redhat.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Alan Cox [Mon, 13 Oct 2008 09:39:46 +0000 (10:39 +0100)]
tty: usb-serial krefs
Use kref in the USB serial drivers so that we don't free tty structures
from under the URB receive handlers as has historically been the case if
you were unlucky. This also gives us a framework for general tty drivers to
use tty_port objects and refcount.
Contains two err->dev_err changes merged together to fix clashes in the
-next tree.
Signed-off-by: Alan Cox <alan@redhat.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Alan Cox [Mon, 13 Oct 2008 09:39:13 +0000 (10:39 +0100)]
tty: Make get_current_tty use a kref
We now return a kref covered tty reference. That ensures the tty structure
doesn't go away when you have a return from get_current_tty. This is not
enough to protect you from most of the resources being freed behind your
back - yet.
[Updated to include fixes for SELinux problems found by Andrew Morton and
an s390 leak found while debugging the former]
Signed-off-by: Alan Cox <alan@redhat.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Alan Cox [Mon, 13 Oct 2008 09:39:01 +0000 (10:39 +0100)]
tty: compare the tty winsize
We always use the real tty one for stuff so the pty one should not be
compared. As we propagate window changes to both it doesn't currently
matter but will when we tidy up the pty termios logic a bit more
Signed-off-by: Alan Cox <alan@redhat.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Alan Cox [Mon, 13 Oct 2008 09:38:18 +0000 (10:38 +0100)]
tty: Add termiox
We need a way to describe the various additional modes and flow control
features that random weird hardware shows up and software such as wine
wants to emulate as Windows supports them.
TCGETX/TCSETX and the termiox ioctl are a SYS5 extension that we might as
well adopt. This patches adds the structures and the basic ioctl interfaces
when the TCGETX etc defines are added for an architecture. Drivers wishing
to use this stuff need to add new methods.
Signed-off-by: Alan Cox <alan@redhat.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Alan Cox [Mon, 13 Oct 2008 09:38:07 +0000 (10:38 +0100)]
tty: ipw need reworking
This came in via another tree and unfortunately is rather broken on
the tty side. Comment the apparent locking problems for someone who knows
the driver to look at.
Fix the termios and other ioctl handling. The driver was calling the wrong
methods for what it wanted to do but the right ones existed so its a simple
fix up.
Signed-off-by: Alan Cox <alan@redhat.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Alan Cox [Mon, 13 Oct 2008 09:37:48 +0000 (10:37 +0100)]
tty: Cris has a nice RS485 ioctl so we should steal it
JP Tosoni observed:
"About a RS485 ioctl: could you consider the attached files which are
already in the Linux kernel (in include/asm-cris). They define a
TIOCSERSETRS485 (ioctl.h), and the data structure (rs485.h)
with allows to specify timings. Sounds just like what we want ?"
and he's right: sort of. Rework the structure to use flag bits and make the
time delay a fixed sized field so we don't get 32/64bit problems. Add the ioctls
to x86 so that people know what to add to their platform of choice.
Signed-off-by: Alan Cox <alan@redhat.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Alan Cox [Mon, 13 Oct 2008 09:37:36 +0000 (10:37 +0100)]
tty: use krefs to protect driver module counts
The tty layer keeps driver module counts that are used so the driver knows
when it can be unloaded. For obvious reasons we want to tie that to the
refcounting properly.
At this point the driver side itself isn't refcounted nicely but we can do
that later and kref the drivers.
Signed-off-by: Alan Cox <alan@redhat.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Alan Cox [Mon, 13 Oct 2008 09:36:40 +0000 (10:36 +0100)]
tty: move tioclinux from a special case
Right now we have ifdefs and hooks in the core ioctl handler for TIOCLINUX
and then test if its a console. This is brain dead. Instead call the
tioclinux helper from the relevant driver ioctl methods.
Signed-off-by: Alan Cox <alan@redhat.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
David Miller [Mon, 13 Oct 2008 09:36:31 +0000 (10:36 +0100)]
serial: allow 8250 to be used on sparc
This requires three changes:
1) Remove !SPARC restriction in Kconfig.
2) Move Sparc specific serial drivers before 8250, so that serial
console devices don't change names on us, even if 8250 finds
devices.
3) Since the Sparc specific serial drivers try to use the
same major/minor device namespace as 8250, some coordination
is necessary. Use the sunserial_*() layer routines to allocate
minor number space within TTY_MAJOR when CONFIG_SPARC.
This has no effect on other platforms.
Thanks to Josip Rodin for bringing up this issue and testing
plus debugging various revisions of this patch.
Signed-off-by: David S. Miller <davem@davemloft.net> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Alan Cox <alan@redhat.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Will Newton [Mon, 13 Oct 2008 09:36:21 +0000 (10:36 +0100)]
8250: remove a few inlines of dubious value
Remove some inlines from various functions that are called once, are too
big to inline, or are called only from slow path code. This saves around
300 bytes of code for me.
Signed-off-by: Will Newton <will.newton@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Alan Cox <alan@redhat.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Alan Cox [Mon, 13 Oct 2008 09:36:11 +0000 (10:36 +0100)]
serial_8250: pci_enable_device fail is not fully handled
<rmk> talking about leaks - I noticed that the 'check return of
pci_enable_dev()' in the 8250 pci resume function finally made it in
despite my objections against it (causing stuff in higher levels to
leak).
Signed-off-by: Alan Cox <alan@redhat.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Jason Wessel [Mon, 13 Oct 2008 09:35:51 +0000 (10:35 +0100)]
usb: fix pl2303 initialization
This patch removes the private check for the termios_initialized for
the pl2303 usb driver. It forced the baud to 9600 on the first call
to pl2303_set_termios()
Based on the tty changes in the 2.6.27 kernel, the termios passed to
the *_set_termios functions is always populated the first time.
This means there is no need to privately initialize the settings the
first time, and doing so will not allow the use of the kernel
parameter "console=ttyUSB0,115200" as an example.
Signed-off-by: Jason Wessel <jason.wessel@windriver.com> Signed-off-by: Alan Cox <alan@redhat.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Alan Cox [Mon, 13 Oct 2008 09:35:33 +0000 (10:35 +0100)]
nozomi: Fix close on error
Nozomi assumes the close method isn't called if open errors. The tty layer
is different to other drives in this respect however. Pointed out by Denis J
Barrow.
Signed-off-by: Alan Cox <alan@redhat.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
David Miller [Mon, 13 Oct 2008 09:35:23 +0000 (10:35 +0100)]
serial: Make uart_port's ioport "unsigned long".
Otherwise the top 32-bits of the resource value get chopped
off on 64-bit systems, and the resulting I/O accesses go to
random places.
Thanks to testing and debugging by Josip Rodin, which helped
track this down.
Signed-off-by: David S. Miller <davem@davemloft.net> Signed-off-by: Alan Cox <alan@redhat.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Miloslav Trmac [Mon, 13 Oct 2008 09:35:15 +0000 (10:35 +0100)]
audit: Handle embedded NUL in TTY input auditing
Data read from a TTY can contain an embedded NUL byte (e.g. after
pressing Ctrl-2, or sent to a PTY). After the previous patch, the data
would be logged only up to the first NUL.
This patch modifies the AUDIT_TTY record to always use the hexadecimal
format, which does not terminate at the first NUL byte. The vast
majority of recorded TTY input data will contain either ' ' or '\n', so
the hexadecimal format would have been used anyway.
Akinobu Mita [Mon, 13 Oct 2008 09:35:05 +0000 (10:35 +0100)]
ip2: avoid add_timer with pending timer
add_timer() is not supposed to be called when the timer is pending.
ip2 driver attempts to avoid that condition by setting and resetting
a flag (TimerOn) in timer function. But there is some gap between
add_timer() and setting TimerOn.
This patch fix this problem by using mod_timer() and remove TimerOn
which has been unnecessary by this change.
Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com> Signed-off-by: Jiri Slaby <jirislaby@gmail.com> Signed-off-by: Alan Cox <alan@redhat.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Jiri Slaby [Mon, 13 Oct 2008 09:34:56 +0000 (10:34 +0100)]
ip2: init/deinit cleanup
Cleanup of module_init/exit:
- mostly whitespace
- remove empty functions
- replace c++ comments
- remove useless prints (module loaded, unloaded)
- mark the calls as __exit and __init
- use break; and return; to save some indent levels after it
- note resource leakage
Jiri Slaby [Mon, 13 Oct 2008 09:34:27 +0000 (10:34 +0100)]
Char: merge ip2main and ip2base
It's pretty useless to have one setup() function separated along with
module_init() which only calls a function from ip2main anyway. Get rid
of ip2base.
Mike Frysinger [Mon, 13 Oct 2008 09:33:16 +0000 (10:33 +0100)]
Blackfin Serial Driver: move common variables out of serial headers and into the serial driver
move common variables out of serial headers and into the serial driver and
rename "nr_ports" to "nr_active_ports" so as to easily differentiate
between BFIN_UART_NR_PORTS (the # of available) and nr_ports (the # of enabled)
Signed-off-by: Mike Frysinger <vapier.adi@gmail.com> Signed-off-by: Bryan Wu <cooloney@kernel.org> Signed-off-by: Alan Cox <alan@redhat.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Julia Lawall [Mon, 13 Oct 2008 09:31:49 +0000 (10:31 +0100)]
drivers/char/hvc_console.c: adjust call to put_tty_driver
The call to put_tty_driver is out of place and is applied to the wrong
argument.
The function enclosing the patched code calls alloc_tty_driver and stores
the result in drv. Subsequently, there are two occurrences of error
handling code, one making a goto to put_tty and one making a goto to
stop_thread. At the point of the first one the assignment hvc_driver = drv
has not yet been executed, and from inspecting the rest of the file it
seems that hvc_driver would be NULL. Thus the current call to
put_tty_driver is useless, and one applied to drv is needed. The goto
stop_thread is in the error handling code for a call to
tty_register_driver, but the error cases in tty_register_driver do not free
its argument, so it should be done here. Thus, I have moved the put_tty
label after the stop_thread label, so that put_tty_driver is called in both
cases.
The semantic match that finds this problem is as follows:
(http://www.emn.fr/x-info/coccinelle/)
// <smpl>
@r exists@
local idexpression x;
expression E,f;
position p1,p2,p3;
identifier l;
statement S;
@@
x = alloc_tty_driver@p1(...)
...
if (x == NULL) S
... when != E = x
when != put_tty_driver(x)
goto@p2 l;
... when != E = x
when != f(...,x,...)
when any
(
return \(0\|x\);
|
return@p3 ...;
)
alloc_tty_driver is called at the beginning of the function containing the
lines of code shown in the patch. Thus, put_tty_driver is needed before
returning in the error handling code.
The semantic match that finds this problem is as follows:
(http://www.emn.fr/x-info/coccinelle/)
// <smpl>
@nr exists@
local idexpression x;
expression E,f;
position p1,p2,p3;
identifier l;
statement S;
@@
x = alloc_tty_driver@p1(...)
...
if (x == NULL) S
... when != E = x
when != put_tty_driver(x)
when != goto l;
(
return \(0\|x\);
|
return@p3 ...;
)
@script:python@
p1 << nr.p1;
p3 << nr.p3;
@@
print "%s: call on line %s not freed or saved before return on line %s" % (p1[0].file,p1[0].line,p3[0].line)
// </smpl>
Signed-off-by: Julia Lawall <julia@diku.dk> Signed-off-by: Alan Cox <alan@redhat.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Thomas Gleixner [Sun, 5 Oct 2008 15:51:52 +0000 (17:51 +0200)]
x86: remove additional_cpus
remove remainder of additional_cpus logic. We now just listen to the
disabled_cpus value like we did for years. disabled_cpus is always >=
0 so no need for an extra check.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Ingo Molnar <mingo@elte.hu>
Ingo Molnar [Sun, 5 Oct 2008 15:12:36 +0000 (17:12 +0200)]
x86: remove additional_cpus configurability
additional_cpus=<x> parameter is dangerous and broken: for example
if we boot additional_cpus=-2 on a stock dual-core system it will
crash the box on bootup.
So reduce the maze of code a bit by removingthe user-configurability
angle.
- define STACKSLOTS_PER_LINE and use it
- define get_bp macro to hide the %%ebp/%%rbp difference
- i386: check task==NULL in dump_trace, like x86_64
- i386: show_trace(NULL, ...) uses current automatically
- x86_64: use [#%d] for die_counter, like i386
- whitespace and comments
Signed-off-by: Alexander van Heukelum <heukelum@fastmail.fm> Signed-off-by: Ingo Molnar <mingo@elte.hu>
dumptrace: x86: consistently include loglevel, print stack switch
- i386 and x86_64: always printk the 'data' parameter
- i386: announce stack switch (irq -> normal)
- i386: check if there is a stack switch before announcing it
There is a warning that 'context' might come out corrupt in early
boot. If this is true it should be fixed, not worked around.
Signed-off-by: Alexander van Heukelum <heukelum@fastmail.fm> Signed-off-by: Ingo Molnar <mingo@elte.hu>
traps: i386: expand clear_mem_error and remove from mach_traps.h
This is the last user of clear_mem_error, which is defined
only on i386. Expand the inline function and remove it from
include/asm-x86/mach-default/mach_traps.h
Signed-off-by: Alexander van Heukelum <heukelum@fastmail.fm> Signed-off-by: Ingo Molnar <mingo@elte.hu>
- set_system_gate on i386 is really set_system_trap_gate
- set_system_gate on x86_64 is really set_system_intr_gate
- ist=0 means no special stack switch is done:
- introduce STACKFAULT_STACK, DOUBLEFAULT_STACK, NMI_STACK,
DEBUG_STACK and MCE_STACK as on x86_64.
- use the _ist variants with XXX_STACK set to zero
- remove set_system_gate
Signed-off-by: Alexander van Heukelum <heukelum@fastmail.fm> Signed-off-by: Ingo Molnar <mingo@elte.hu>
traps: x86: correct copy/paste bug: a trap is a GATE_TRAP
Fix copy/paste/forgot-to-edit bug in desc.h.
Signed-off-by: Alexander van Heukelum <heukelum@fastmail.fm> Signed-off-by: Ingo Molnar <mingo@elte.hu>
Make the x86_64-version and the i386-version of do_debug
more similar.
- introduce preempt_conditional_sti/cli to i386. The preempt-count
is now elevated during the trap handler, like on x86_64. It
does not run on a separate stack, however.
- replace an open-coded "send_sigtrap"
- copy some comments
Signed-off-by: Alexander van Heukelum <heukelum@fastmail.fm> Signed-off-by: Ingo Molnar <mingo@elte.hu>
x86, traps: split out math_error and simd_math_error
Split out math_error from do_coprocessor_error and simd_math_error
from do_simd_coprocessor_error, like on i386. While at it, add the
"error_code" parameter to do_coprocessor_error, do_simd_coprocessor_error
and do_spurious_interrupt_bug.
This does not change the generated code, but brings the declarations in
line with all the other trap handlers.
Signed-off-by: Alexander van Heukelum <heukelum@fastmail.fm> Signed-off-by: Ingo Molnar <mingo@elte.hu>
Vegard Nossum [Fri, 3 Oct 2008 15:54:25 +0000 (17:54 +0200)]
x86: fix virt_addr_valid() with CONFIG_DEBUG_VIRTUAL=y, v2
virt_addr_valid() calls __pa(), which calls __phys_addr(). With
CONFIG_DEBUG_VIRTUAL=y, __phys_addr() will kill the kernel if the
address *isn't* valid. That's clearly wrong for virt_addr_valid().
We also incorporate the debugging checks into virt_addr_valid().
Chuck Ebbert [Thu, 2 Oct 2008 19:30:07 +0000 (15:30 -0400)]
x86: allow number of additional hotplug CPUs to be set at compile time, V2
x86: allow number of additional hotplug CPUs to be set at compile time, V2
The default number of additional CPU IDs for hotplugging is determined
by asking ACPI or mptables how many "disabled" CPUs there are in the
system, but many systems get this wrong so that e.g. a uniprocessor
machine gets an extra CPU allocated and never switches to single CPU
mode.
And sometimes CPU hotplugging is enabled only for suspend/hibernate
anyway, so the additional CPU IDs are not wanted. Allow the number
to be set to zero at compile time.
Also, force the number of extra CPUs to zero if hotplugging is disabled
which allows removing some conditional code.
Tested on uniprocessor x86_64 that ACPI claims has a disabled processor,
with CPU hotplugging configured.
("After" has the number of additional CPUs set to 0)
Before: NR_CPUS: 512, nr_cpu_ids: 2, nr_node_ids 1
After: NR_CPUS: 512, nr_cpu_ids: 1, nr_node_ids 1
[Changed the name of the option and the prompt according to Ingo's
suggestion.]
Krzysztof Helt [Tue, 30 Sep 2008 21:17:51 +0000 (23:17 +0200)]
x86: do not allow to optimize flag_is_changeable_p() (rev. 2)
The flag_is_changeable_p() is used by
has_cpuid_p() which can return different results
in the code sequence below:
if (!have_cpuid_p())
identify_cpu_without_cpuid(c);
/* cyrix could have cpuid enabled via c_identify()*/
if (!have_cpuid_p())
return;
Otherwise, the gcc 3.4.6 optimizes these two calls
into one which make the code not working correctly.
Cyrix cpus have the CPUID instruction enabled before
the second call to the have_cpuid_p() but
it is not detected due to the gcc optimization.
Thus the ARR registers (mtrr like) are not detected
on such a cpu.
Signed-off-by: Krzysztof Helt <krzysztof.h1@wp.pl> Signed-off-by: Ingo Molnar <mingo@elte.hu>
Pekka Enberg [Thu, 3 Apr 2008 13:40:48 +0000 (16:40 +0300)]
x86: __show_registers() and __show_regs() API unification
Currently the low-level function to dump user-passed registers on i386 is
called __show_registers() whereas on x86-64 it's called __show_regs(). Unify
the API to simplify porting of kmemcheck to x86-64.
Jack Steiner [Mon, 29 Sep 2008 13:45:29 +0000 (08:45 -0500)]
x86, UV: new UV genapic functions for x2apic
Add functions that use the infrastructure added by the x2apic code. These
functions were originally stubbed out since the UV code went into the
tree prior to the x2apic code.
Signed-off-by: Jack Steiner <steiner@sgi.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
Commit 4a701737 ("x86: move prefill_possible_map calling early, fix")
is the wrong fix: prefill_possible_map() needs to be available
even when CONFIG_HOTPLUG_CPU is not set. A followon patch will do that.
Fix this correctly by making prefill_possible_map() available even when
CONFIG_HOTPLUG_CPU is not set. The function is needed so that
the number of possible CPUs can be determined.
Tested on uniprocessor machine with CPU hotplug disabled.