- idle task becomes a pseudo task which is never scheduled. It is never put on
any run queue and never enters userspace. An entry for this task still remains
in the process table for time accounting
- Instead of panicing if there is not process to schedule, pick_proc() returns
NULL which is a signal to put the cpu in an idle state and set everything in
such a way that after receiving and interrupt it looks like idle task was
preempted
- idle task is set non-preemptible to avoid handling in the timer interrupt code
which make userspace scheduling simpler as idle task does not need to be
handled as a special case.
- no longer have kernel have its own page table that is loaded
on every kernel entry (trap, interrupt, exception). the primary
purpose is to reduce the number of required reloads.
Result:
- kernel can only access memory of process that was running when
kernel was entered
- kernel must be mapped into every process page table, so traps to
kernel keep working
Problem:
- kernel must often access memory of arbitrary processes (e.g. send
arbitrary processes messages); this can't happen directly any more;
usually because that process' page table isn't loaded at all, sometimes
because that memory isn't mapped in at all, sometimes because it isn't
mapped in read-write.
So:
- kernel must be able to map in memory of any process, in its own
address space.
Implementation:
- VM and kernel share a range of memory in which addresses of
all page tables of all processes are available. This has two purposes:
. Kernel has to know what data to copy in order to map in a range
. Kernel has to know where to write the data in order to map it in
That last point is because kernel has to write in the currently loaded
page table.
- Processes and kernel are separated through segments; kernel segments
haven't changed.
- The kernel keeps the process whose page table is currently loaded
in 'ptproc.'
- If it wants to map in a range of memory, it writes the value of the
page directory entry for that range into the page directory entry
in the currently loaded map. There is a slot reserved for such
purposes. The kernel can then access this memory directly.
- In order to do this, its segment has been increased (and the
segments of processes start where it ends).
- In the pagefault handler, detect if the kernel is doing
'trappable' memory access (i.e. a pagefault isn't a fatal
error) and if so,
- set the saved instruction pointer to phys_copy_fault,
breaking out of phys_copy
- set the saved eax register to the address of the page
fault, both for sanity checking and for checking in
which of the two ranges that phys_copy was called
with the fault occured
- Some boot-time processes do not have their own page table,
and are mapped in with the kernel, and separated with
segments. The kernel detects this using HASPT. If such a
process has to be scheduled, any page table will work and
no page table switch is done.
Major changes in kernel are
- When accessing user processes memory, kernel no longer
explicitly checks before it does so if that memory is OK.
It simply makes the mapping (if necessary), tries to do the
operation, and traps the pagefault if that memory isn't present;
if that happens, the copy function returns EFAULT.
So all of the CHECKRANGE_OR_SUSPEND macros are gone.
- Kernel no longer has to copy/read and parse page tables.
- A message copying optimisation: when messages are copied, and
the recipient isn't mapped in, they are copied into a buffer
in the kernel. This is done in QueueMess. The next time
the recipient is scheduled, this message is copied into
its memory. This happens in schedcheck().
This eliminates the mapping/copying step for messages, and makes
it easier to deliver messages. This eliminates soft_notify.
- Kernel no longer creates a page table at all, so the vm_setbuf
and pagetable writing in memory.c is gone.
Minor changes in kernel are
- ipc_stats thrown out, wasn't used
- misc flags all renamed to MF_*
- NOREC_* macros to enter and leave functions that should not
be called recursively; just sanity checks really
- code to fully decode segment selectors and descriptors
to print on exceptions
- lots of vmassert()s added, only executed if DEBUG_VMASSERT is 1
Kernel:
o Remove s_ipc_sendrec, instead using s_ipc_to for all send primitives
o Centralize s_ipc_to bit manipulation,
- disallowing assignment of bits pointing to unused priv structs;
- preventing send-to-self by not setting bit for own priv struct;
- preserving send mask matrix symmetry in all cases
o Add IPC send mask checks to SENDA, which were missing entirely somehow
o Slightly improve IPC stats accounting for SENDA
o Remove SYSTEM from user processes' send mask
o Half-fix the dependency between boot image order and process numbers,
- correcting the table order of the boot processes;
- documenting the order requirement needed for proper send masks;
- warning at boot time if the order is violated
RS:
o Add support in /etc/drivers.conf for servers that talk to user processes,
- disallowing IPC to user processes if no "ipc" field is present
- adding a special "USER" label to explicitly allow IPC to user processes
o Always apply IPC masks when specified; remove -i flag from service(8)
o Use kernel send mask symmetry to delay adding IPC permissions for labels
that do not exist yet, adding them to that label's process upon creation
o Add VM to ipc permissions list for rtl8139 and fxp in drivers.conf
Left to future fixes:
o Removal of the table order vs process numbers dependency altogether,
possibly using per-process send list structures as used for SYSTEM calls
o Proper assignment of send masks to boot processes;
some of the assigned (~0) masks are much wider than necessary
o Proper assignment of IPC send masks for many more servers in drivers.conf
o Removal of the debugging warning about the now legitimate case where RS's
add_forward_ipc cannot find the IPC destination's label yet
give every process a full pagetable by default now.
first step to disabling kernel page table code (processes
might not have page tables -> no address translation).
now used for printing diagnostic messages through the kernel message
buffer. this lets processes print diagnostics without sending messages
to tty and log directly, simplifying the message protocol a lot and
reducing difficulties with deadlocks and other situations in which
diagnostics are blackholed (e.g. grants don't work). this makes
DIAGNOSTICS(_S), ASYN_DIAGNOSTICS and DIAG_REPL obsolete, although tty
and log still accept the codes for 'old' binaries. This also simplifies
diagnostics in several servers and drivers - only tty needs its own
kputc() now.
. simplifications in vfs, and some effort to get the vnode references
right (consistent) even during shutdown. m_mounted_on is now NULL
for root filesystems (!) (the original and new root), a less awkward
special case than 'm_mounted_on == m_root_node'. root now has exactly
one reference, to root, if no files are open, just like all other
filesystems. m_driver_e is unused.
. introduce FULLVM flag: MEMORY and the initial MFS
get their own full address spaces, making their stacks
and heaps not preallocated (well, freed after VM has
initialized it) and letting them allocate more dynamically.
MEMORY in particular needs this to map in physical memory
using its own page table, without having to allocate.
mainly in the kernel and headers. This split based on work by
Ingmar Alting <iaalting@cs.vu.nl> done for his Minix PowerPC architecture
port.
. kernel does not program the interrupt controller directly, do any
other architecture-dependent operations, or contain assembly any more,
but uses architecture-dependent functions in arch/$(ARCH)/.
. architecture-dependent constants and types defined in arch/$(ARCH)/include.
. <ibm/portio.h> moved to <minix/portio.h>, as they have become, for now,
architecture-independent functions.
. int86, sdevio, readbios, and iopenable are now i386-specific kernel calls
and live in arch/i386/do_* now.
. i386 arch now supports even less 86 code; e.g. mpx86.s and klib86.s have
gone, and 'machine.protected' is gone (and always taken to be 1 in i386).
If 86 support is to return, it should be a new architecture.
. prototypes for the architecture-dependent functions defined in
kernel/arch/$(ARCH)/*.c but used in kernel/ are in kernel/proto.h
. /etc/make.conf included in makefiles and shell scripts that need to
know the building architecture; it defines ARCH=<arch>, currently only
i386.
. some basic per-architecture build support outside of the kernel (lib)
. in clock.c, only dequeue a process if it was ready
. fixes for new include files
files deleted:
. mpx/klib.s - only for choosing between mpx/klib86 and -386
. klib86.s - only for 86
i386-specific files files moved (or arch-dependent stuff moved) to arch/i386/:
. mpx386.s (entry point)
. klib386.s
. sconst.h
. exception.c
. protect.c
. protect.h
. i8269.c
any number of kernel calls.
Allowed kernel calls are stored in table.c for every image process as a
variably-sized array of allowed calls. This is used to fill the bitmap
of size determined at compile time by the number of kernel calls. This
filling is done by main.c. There is a special call called SYS_ALL_CALLS
which fills the bitmap of allowed calls completely, if that is the only
entry in the array.
. Also allow receive() to be done from kernel processes, not just
sendrec(). This is because receive()s can't harm the kernel processes,
but are done from the CLOCK task (without sendrec()).
enforced. If a call is denied, this will be kprinted. Please report any such
errors, so that I can adjust the mask before returning errors instead of
warnings.
Wrote CMOS driver. All CMOS code from FS has been removed. Currently the
driver only supports get time calls. Set time is left out as an exercise
for the book readers ... startup scripts were updated because the CMOS driver
is needed early on. (IS got same treatment.) Don't forget to run MAKEDEV cmos
in /dev/, otherwise the driver cannot be loaded.
The user needs to set label=... to choose the driver of his or her choice.
This driver will be mapped onto the controller that is set in controller=...
Minor cleanup of kernel source code (boot image table now is static).
This was caused by a change in the shared driver code. Not log's fault.
Renamed #definitions of driver process numbers, e.g., TTY now is TTY_PROC_NR.
All known (special) processes now have consistent naming scheme. Kernel tasks
don't follow this scheme.
