This patch implements soft interrupts.  Interrupt enabling and disabling no
longer map to sigprocmask.  Rather, a flag is set indicating whether
interrupts may be handled.  If a signal comes in and interrupts are marked as
OK, then it is handled normally.  If interrupts are marked as off, then the
signal handler simply returns after noting that a signal needs handling.  When
interrupts are enabled later on, this pending signals flag is checked, and the
IRQ handlers are called at that point.

The point of this is to reduce the cost of local_irq_save et al, since they
are very much more common than the signals that they are enabling and
disabling.  Soft interrupts produce a speed-up of ~25% on a kernel build.

Subtleties -

    UML uses sigsetjmp/siglongjmp to switch contexts.  sigsetjmp has been
    wrapped in a save_flags-like macro which remembers the interrupt state at
    setjmp time, and restores it when it is longjmp-ed back to.

    The enable_signals function has to loop because the IRQ handler
    disables interrupts before returning.  enable_signals has to return with
    signals enabled, and signals may come in between the disabling and the
    return to enable_signals.  So, it loops for as long as there are pending
    signals, ensuring that signals are enabled when it finally returns, and
    that there are no pending signals that need to be dealt with.
Signed-off-by: NJeff Dike <jdike@addtoit.com>
Cc: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

The serial UML OS-abstraction layer patch (um/kernel dir).

This moves all systemcalls from time.c file under os-Linux dir and joins
time.c and tine_kernel.c files
Signed-off-by: NGennady Sharapov <Gennady.V.Sharapov@intel.com>
Signed-off-by: NJeff Dike <jdike@addtoit.com>
Cc: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

The serial UML OS-abstraction layer patch (um/kernel dir).

This moves all systemcalls from signal_user.c file under os-Linux dir
Signed-off-by: NGennady Sharapov <Gennady.V.Sharapov@intel.com>
Signed-off-by: NJeff Dike <jdike@addtoit.com>
Cc: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

The serial UML OS-abstraction layer patch (um/kernel dir).

This moves all systemcalls from main.c file under os-Linux dir and joins mem.c
and um_arch.c files.
Signed-off-by: NGennady Sharapov <Gennady.V.Sharapov@intel.com>
Signed-off-by: NJeff Dike <jdike@addtoit.com>
Cc: Paolo Giarrusso <blaisorblade@yahoo.it>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

Apparently, GDB gets confused when we do an execvp() on ourselves.

Since it's simply done to allocate further space for command line arguments
(which we'll use to allow gathering the startup command line for guest
processes through the host), allow the user to disable that to get a
debuggable UML binary.
Signed-off-by: NPaolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
Cc: Jeff Dike <jdike@addtoit.com>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

kmalloc wasn't being disabled during panic.  This patch ensures that, no
matter how UML is exiting, it is disabled.  This matters because part of the
cleanup is to remove the umid file, which involves readdir, which calls
malloc.  This must map to libc malloc, rather than kmalloc or vmalloc.
Signed-off-by: NJeff Dike <jdike@addtoit.com>
Cc: Paolo Giarrusso <blaisorblade@yahoo.it>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

A few files include the same header twice.
Signed-off-by: NJeff Dike <jdike@addtoit.com>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

We need to disable signals on exit in all cases, not just when rebooting.
Signed-off-by: NJeff Dike <jdike@addtoit.com>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

We should turn off kmalloc when getting a fatal signal regardless of the mode
we're in.
Signed-off-by: NJeff Dike <jdike@addtoit.com>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

Initial git repository build. I'm not bothering with the full history,
even though we have it. We can create a separate "historical" git
archive of that later if we want to, and in the meantime it's about
3.2GB when imported into git - space that would just make the early
git days unnecessarily complicated, when we don't have a lot of good
infrastructure for it.

Let it rip!