- Set the correct value scp->font_size in init_scp().
- Set scp->font_size to FONT_NONE for VGA_MODEX.
Interim fix for a font problem:
- A kludge to display the correct font on some video cards.
We should be able to load multiple fonts to the VGA plane #2 and switch
between fonts by setting the font select register in the VGA sequencer.
It appears that the current code isn't functioning as expected on
some VGA cards (I have reports on Millenium and Mach64 cards). This is
either a bug in syscons or a hardware compatibility problem ;-<
This kludge will always load only one font set at a time and always use
the font page #0 on the plane #2. It is an interim kludge until
we find the exact cause and solution.
Small adjustment for mouse cursor handling:
- Turn off the mouse cursor early when changing video modes.
Video mode switch fixes:
- Stop the screen saver when changing video modes.
- Enclose the critical section with a pair of spltty()/splx().
- A kludge to prevent scrn_update() from accessing video memory in less-
critical sections in video mode change; artificially turn on the
UNKNOWN_MODE flag.
PR: bin/5899, bin/5907
Tested by: ache and a couple of users
OKed by: sos
* Figure out UTC relative to boottime. Four new functions provide
time relative to boottime.
* move "runtime" into struct proc. This helps fix the calcru()
problem in SMP.
* kill mono_time.
* add timespec{add|sub|cmp} macros to time.h. (XXX: These may change!)
* nanosleep, select & poll takes long sleeps one day at a time
Reviewed by: bde
Tested by: ache and others
- Attempt to handle PCI devices where the interrupt is
an ISA/EISA interrupt according to the mp table.
- Attempt to handle multiple IO APIC pins connected to
the same PCI or ISA/EISA interrupt source. Print a
warning if this happens, since performance is suboptimal.
This workaround is only used for PCI devices.
With these two workarounds, the -SMP kernel is capable of running on
my Asus P/I-P65UP5 motherboard when version 1.4 of the MP table is disabled.
"time" wasn't a atomic variable, so splfoo() protection were needed
around any access to it, unless you just wanted the seconds part.
Most uses of time.tv_sec now uses the new variable time_second instead.
gettime() changed to getmicrotime(0.
Remove a couple of unneeded splfoo() protections, the new getmicrotime()
is atomic, (until Bruce sets a breakpoint in it).
A couple of places needed random data, so use read_random() instead
of mucking about with time which isn't random.
Add a new nfs_curusec() function.
Mark a couple of bogosities involving the now disappeard time variable.
Update ffs_update() to avoid the weird "== &time" checks, by fixing the
one remaining call that passwd &time as args.
Change profiling in ncr.c to use ticks instead of time. Resolution is
the same.
Add new function "tvtohz()" to avoid the bogus "splfoo(), add time, call
hzto() which subtracts time" sequences.
Reviewed by: bde
_KPOSIX_PRIORITY_SCHEDULING options to work. Changes:
Change all "posix4" to "p1003_1b". Misnamed files are left
as "posix4" until I'm told if I can simply delete them and add
new ones;
Add _POSIX_PRIORITY_SCHEDULING system calls for FreeBSD and Linux;
Add man pages for _POSIX_PRIORITY_SCHEDULING system calls;
Add options to LINT;
Minor fixes to P1003_1B code during testing.
They are atomic, but return in essence what is in the "time" variable.
gettime() is now a macro front for getmicrotime().
Various patches to use the two new functions instead of the various
hacks used in their absence.
Some puntuation and grammer patches from Bruce.
A couple of XXX comments.
everything is contained inside #ifdef VM86, so this option must be
present in the config file to use this functionality.
Thanks to Tor Egge, these changes should work on SMP machines. However,
it may not be throughly SMP-safe.
Currently, the only BIOS calls made are memory-sizing routines at bootup,
these replace reading the RTC values.
- Implement proper EISA probing.
- Better support for the new transputer based host cards.
- use standard termios settings, one can use the intial/lock devices.
- use a simple bcopy since some cards/systems apparently don't support
32 bit accesses.
- hard reset and halt host card CPU prior to download in case of a soft
restart.
- recognize new remote module types (ASIC vs. CD1400 based)
- a number of cosmetic changes (my fault, not Nick's)
Submitted by: Nick Sayer <nsayer@quack.kfu.com>
Don't try to flush buffers if the drive says it has none.
More error checking and reporting.
Hack: if drive hangs, it can be reset by issuing a mt -f device offline.
I've been able to make several 4G backups. However there is still problems
with some configurations. It is not clear if it is hardware or driver
problems yet.
problems. Tor Egge and others have helped with various VM bugs
lately, but don't blame him -- blame me!!!
pmap.c:
1) Create an object for kernel page table allocations. This
fixes a bogus allocation method previously used for such, by
grabbing pages from the kernel object, using bogus pindexes.
(This was a code cleanup, and perhaps a minor system stability
issue.)
pmap.c:
2) Pre-set the modify and accessed bits when prudent. This will
decrease bus traffic under certain circumstances.
vfs_bio.c, vfs_cluster.c:
3) Rather than calculating the beginning virtual byte offset
multiple times, stick the offset into the buffer header, so
that the calculated offset can be reused. (Long long multiplies
are often expensive, and this is a probably unmeasurable performance
improvement, and code cleanup.)
vfs_bio.c:
4) Handle write recursion more intelligently (but not perfectly) so
that it is less likely to cause a system panic, and is also
much more robust.
vfs_bio.c:
5) getblk incorrectly wrote out blocks that are incorrectly sized.
The problem is fixed, and writes blocks out ONLY when B_DELWRI
is true.
vfs_bio.c:
6) Check that already constituted buffers have fully valid pages. If
not, then make sure that the B_CACHE bit is not set. (This was
a major source of Sig-11 type problems.)
vfs_bio.c:
7) Fix a potential system deadlock due to an incorrectly specified
sleep priority while waiting for a buffer write operation. The
change that I made opens the system up to serious problems, and
we need to examine the issue of process sleep priorities.
vfs_cluster.c, vfs_bio.c:
8) Make clustered reads work more correctly (and more completely)
when buffers are already constituted, but not fully valid.
(This was another system reliability issue.)
vfs_subr.c, ffs_inode.c:
9) Create a vtruncbuf function, which is used by filesystems that
can truncate files. The vinvalbuf forced a file sync type operation,
while vtruncbuf only invalidates the buffers past the new end of file,
and also invalidates the appropriate pages. (This was a system reliabiliy
and performance issue.)
10) Modify FFS to use vtruncbuf.
vm_object.c:
11) Make the object rundown mechanism for OBJT_VNODE type objects work
more correctly. Included in that fix, create pager entries for
the OBJT_DEAD pager type, so that paging requests that might slip
in during race conditions are properly handled. (This was a system
reliability issue.)
vm_page.c:
12) Make some of the page validation routines be a little less picky
about arguments passed to them. Also, support page invalidation
change the object generation count so that we handle generation
counts a little more robustly.
vm_pageout.c:
13) Further reduce pageout daemon activity when the system doesn't
need help from it. There should be no additional performance
decrease even when the pageout daemon is running. (This was
a significant performance issue.)
vnode_pager.c:
14) Teach the vnode pager to handle race conditions during vnode
deallocations.
on the IOAPIC being connected to the 8254 timer interrupt.
Verify that timer interrupts are delivered. If they aren't, attempt
a fallback to mixed mode (i.e. routing the timer interrupt via the 8259 PIC).
Gee, I wish there was a better way to run makesyscalls.sh so that
a make world finds missing things like this. Running it manually
sucks.
Pointed out by: Peter Dufault
previous commit. Opportunities to clean pages were often missed,
and leaving of the idle state was sometimes delayed until the next
interrupt (after any that occurred while cleaning).
Fixed an unstaticization, a syntax error and a style bug in the
previous commit.
slice number passed in by the bootblocks. This means the kernel will
not use the compatability slice to obtain the root filesystem when
booting from a sliced disk.
Use the extraction macros from reboot.h rather than stating them in full
again.
has been some bitrot and incorrect assumptions in the vfs_bio code. These
problems have manifest themselves worse on NFS type filesystems, but can
still affect local filesystems under certain circumstances. Most of
the problems have involved mmap consistancy, and as a side-effect broke
the vfs.ioopt code. This code might have been committed seperately, but
almost everything is interrelated.
1) Allow (pmap_object_init_pt) prefaulting of buffer-busy pages that
are fully valid.
2) Rather than deactivating erroneously read initial (header) pages in
kern_exec, we now free them.
3) Fix the rundown of non-VMIO buffers that are in an inconsistent
(missing vp) state.
4) Fix the disassociation of pages from buffers in brelse. The previous
code had rotted and was faulty in a couple of important circumstances.
5) Remove a gratuitious buffer wakeup in vfs_vmio_release.
6) Remove a crufty and currently unused cluster mechanism for VBLK
files in vfs_bio_awrite. When the code is functional, I'll add back
a cleaner version.
7) The page busy count wakeups assocated with the buffer cache usage were
incorrectly cleaned up in a previous commit by me. Revert to the
original, correct version, but with a cleaner implementation.
8) The cluster read code now tries to keep data associated with buffers
more aggressively (without breaking the heuristics) when it is presumed
that the read data (buffers) will be soon needed.
9) Change to filesystem lockmgr locks so that they use LK_NOPAUSE. The
delay loop waiting is not useful for filesystem locks, due to the
length of the time intervals.
10) Correct and clean-up spec_getpages.
11) Implement a fully functional nfs_getpages, nfs_putpages.
12) Fix nfs_write so that modifications are coherent with the NFS data on
the server disk (at least as well as NFS seems to allow.)
13) Properly support MS_INVALIDATE on NFS.
14) Properly pass down MS_INVALIDATE to lower levels of the VM code from
vm_map_clean.
15) Better support the notion of pages being busy but valid, so that
fewer in-transit waits occur. (use p->busy more for pageouts instead
of PG_BUSY.) Since the page is fully valid, it is still usable for
reads.
16) It is possible (in error) for cached pages to be busy. Make the
page allocation code handle that case correctly. (It should probably
be a printf or panic, but I want the system to handle coding errors
robustly. I'll probably add a printf.)
17) Correct the design and usage of vm_page_sleep. It didn't handle
consistancy problems very well, so make the design a little less
lofty. After vm_page_sleep, if it ever blocked, it is still important
to relookup the page (if the object generation count changed), and
verify it's status (always.)
18) In vm_pageout.c, vm_pageout_clean had rotted, so clean that up.
19) Push the page busy for writes and VM_PROT_READ into vm_pageout_flush.
20) Fix vm_pager_put_pages and it's descendents to support an int flag
instead of a boolean, so that we can pass down the invalidate bit.
f00f_hack has run.
Use the global r_idt descriptor in f00f_hack when in SMP mode,
so the APs find the relocated interrupt descriptor table.
Submitted by: Partially from David A Adkins <adkin003@tc.umn.edu>
interrupts are masked, and EOI is sent iff the corresponding ISR bit
is set in the local apic. If the CPU cannot obtain the interrupt
service lock (currently the global kernel lock) the interrupt is
forwarded to the CPU holding that lock.
Clock interrupts now have higher priority than other slow interrupts.
the signal handling latency for cpu-bound processes that performs very
few system calls.
The IPI for forcing an additional software trap is no longer dependent upon
BETTER_CLOCK being defined.
than rolling it's own. This means that it now uses the "safe"
exec_map_first_page() to get the ld.so headers rather than risking a panic
on a page fault failure (eg: NFS server goes down).
Since all the ELF tools go to a lot of trouble to make sure everything
lives in the first page for executables, this is a win. I have not seen
any ELF executable on any system where all the headers didn't fit in the
first page with lots of room to spare.
I have been running variations of this code for some time on my pure ELF
systems.
It does endeed work, but there is still some problems to solve.
I get a "nonrecovered data error" from time to time, but besides
this it has backed up several Gigs allready.
Please report any success/failure directly to me.
Thanks to Warner Losh for providing a drive to use in writing
this driver!
2) Do not unnecessarily force page blocking when paging
pages out.
3) Further improve swap pager performance and correctness,
including fixing the paging in progress deadlock (except
in severe I/O error conditions.)
4) Enable vfs_ioopt=1 as a default.
5) Fix and enable the page prezeroing in SMP mode.
All in all, SMP systems especially should show a significant
improvement in "snappyness."
it runs at a constant frequency. This was less of an issue before,
because the TSC only interpolated in the HZ intervals, but now where
the timecounter is used all the way, this becomes much more visible.
Nit: Fix a printf which triggered the bde-filter.
in a way identically as before.) I had problems with the system properly
handling the number of vnodes when there is alot of system memory, and the
default VM_KMEM_SIZE. Two new options "VM_KMEM_SIZE_SCALE" and
"VM_KMEM_SIZE_MAX" have been added to support better auto-sizing for systems
with greater than 128MB.
Add some accouting for vm_zone memory allocations, and provide properly
for vm_zone allocations out of the kmem_map. Also move the vm_zone
allocation stats to the VM OID tree from the KERN OID tree.
signals delivered to a process writing to the audio device the
system: if you try
cat /dev/zero > /dev/dsp (or cat /dev/zero > /dev/pcaudio)
and press Ctrl-C : for a second or two the system appears to freeze
(e.g. the cursor will disappear if you move the mouse, xclock
blocks, etc.). I think that interrupts etc. still run so the problem
is not too terrible, but still annoying
[ The problems appears to also be in isa/pcaudio.c, though that is ignored ]
Submitted by: Luigi Rizzo <luigi@labinfo.iet.unipi.it>
Highlights:
* Simple model for underlying hardware.
* Hardware basis for timekeeping can be changed on the fly.
* Only one hardware clock responsible for TOD keeping.
* Provides a real nanotime() function.
* Time granularity: .232E-18 seconds.
* Frequency granularity: .238E-12 s/s
* Frequency adjustment is continuous in time.
* Less overhead for frequency adjustment.
* Improves xntpd performance.
Reviewed by: bde, bde, bde
Uncommented css0. It compiles OK.
Moved trix0 so that it compiles OK when uncommented. Uncommented
it. Drivers with the same interrupt handler must be together in
config files so that config(8)'s simple avoidance of redundant
declarations of interrupt handlers works (config emits a declaration
unless it would duplicate the previous one).
Commented out NO_LKM. Negative options should not be configured
in LINT. There should be no negative options for subsystems.
LKMs should never have been standard or the default.
select/poll and DEVFS changes, which are limited to an include/define
in sound.h and the actual select/poll implementation in sound.c
[ This commit is blind, but the code is similar enough that there will
hopefully be no problems. ]
The differences Terrys patch and this patch are:
* Remove a lot of un-needed comments.
* Don't put l_hotchar at the front of stuct linesw, there is no need to.
* Use the #defines for the hotchar in the SLIP and PPP line disciplines
with macros. This breaks if the functions are replaced by macros with
unsuitable semantics. Define a MAX() macro unconditionally instead.
max() is unsuitable since we need a constant expression. Don't define
MIN() - we never used min().
is "acquired". This fixes a TSC biasing error of about 10 msec when
pcaudio is active.
Update `time' before calling hardclock() when timer0 is being released.
This is not known to be important.
Added some delays in writertc(). Efficiency is not critical here, unlike
in rtcin(), and we already use conservative delays there.
Don't touch the hardware when machdep.i8254_freq is being changed but
the maximum count wouldn't change. This fixes jitter of up to 10 msec
for most small adjustments to machdep.i8254_freq. When the maximum
count needs to change, the hardware should be adjusted more carefully.
i386_set_ioperm(). Don't use a magic number for the bound.
Fixed missing bounds checking in i386_get_ioperm(). Don't use a
magic number for the bound elsewhere in this function.
Removed some bogus initializers.
this using option "-b" to the boot blocks. It is smartest to compile
a font into your kernel (See LINT), but not mandatory, but apart from
the cursor you will see nothing on the screen until you load a font.
This mode allows XF86_VGA16 to run in 800x600 mode on otherwise unsupported
graphics hardware.
A number of buglets in the cursor handling in syscons may become
visible this way.
actually faster (more than 20% faster for zeroing 1 MB at boot time).
This fixes pessimized copying and zeroing on K6's and perhaps on other
CPUs that are misclassified as i586's.
mode switch in ioctl.
Possibly related to PR: kern/4271
- A kludge: initialize scp->xpixel and ypixel even in the text mode.
If the console enters the `unknown' graphics mode via the ioctl KDSETMODE
(KD_GRAPHICS), these fields are not set (because syscons cannot know
the correct values), but set_mouse_pos() need to refer to these field
to adjust the mouse position.
- Turn off MOUSE_VISIBLE when switching video mode by ioctl.
- another new option: SC_MOUSE_CHAR
Define the first character code of four consecutive codes to be used for
the mouse cursor. Default codes are 0xd0 through 0xd3. Beware that
if you decide to use any codes outside the range of 0xc0-0xdf,
the mouse cursor may not look good, because of the way VGA displays
characters in 9-dot-wide character cells.
Requested by several people.
(This patch was tested by a person who recently reported, in the -current
ML, a page fault problem in the kernel (draw_mouse_iamge()) after
X server shutdown. The patch cured his problem.)
Don't touch/update the screen while manipulating font data.
Possibly related to PR: kern/4271
- Set up VGA in alphanumeric mode rather than graphics mode when
loading font into video memory. This will drastically reduce flicker.
PR: bin/2977
- Set up scp->font_size properly during video mode switch caused by
ioctl.
separate routine: scupdate() called from scrn_timer().
- Make sure that the screen is updated for the low-level console
routines sccngetc() and sccncheckc(). A new routine, sccnupdate(),
is introduced and will call scupdate() above.
Requested by: bde and msmith
OKed by: sos
from the low-level console routines sccngetc() and sccncheckc().
Submitted by: bde (a long time ago)
- Don't try to ring bell and immediately return from do_bell() while
device probe is in progress at boot time; the timeout queue is not
functional yet.
PR: kern/2424
- Stop running the screen saver after panic() is called: check
if `panicstr' is non-NULL during scrn_timer().
PR: kern/5314
- A new option: SC_DISABLE_REBOOT
The reboot key (usually Ctl-Alt-Del) will be ignored if this option
is defined. You may still have the reboot key defined in the keymap and
it won't cause error when the keymap is loaded, but it will be quietly
treated as nop.
OKed by: sos
was supplied to the kernel when booting, ignore any 'quit' commands in the
userconfig script.
This provides an escape mechanism whereby a broken userconfig script may
be worked around.
----
I've worked to enhance the connect() patches.
I've just tested this with the Linux JDK appletviewer on an applet
that does a lot of connects, and it works as well as during my
previous tests.
The connect() patch is now a merge between my older patch and the
OpenBSD stuff. It ensures that any async error is returned by
connect() instead of getsockopt(SOL_SOCKET, SO_ERROR) as reasonnable
systems do.
There are also minor patches to implement IPPROTO_TCP for
get/setsocktopt(). These are also tested (with Linux Apache).
----
I would appreciate any feedback regarding these changes, as they'd
be very useful in 2.2.6.
Submitted by: pb@fasterix.freenix.org (Pierre Beyssac)
of the various ad-hoc schemes.
2) When bringing in UPAGES, the pmap code needs to do another vm_page_lookup.
3) When appropriate, set the PG_A or PG_M bits a-priori to both avoid some
processor errata, and to minimize redundant processor updating of page
tables.
4) Modify pmap_protect so that it can only remove permissions (as it
originally supported.) The additional capability is not needed.
5) Streamline read-only to read-write page mappings.
6) For pmap_copy_page, don't enable write mapping for source page.
7) Correct and clean-up pmap_incore.
8) Cluster initial kern_exec pagin.
9) Removal of some minor lint from kern_malloc.
10) Correct some ioopt code.
11) Remove some dead code from the MI swapout routine.
12) Correct vm_object_deallocate (to remove backing_object ref.)
13) Fix dead object handling, that had problems under heavy memory load.
14) Add minor vm_page_lookup improvements.
15) Some pages are not in objects, and make sure that the vm_page.c can
properly support such pages.
16) Add some more page deficit handling.
17) Some minor code readability improvements.
so that it is possible for kdump and truss to include them both. Use
#defines from pcvt_ioctl.h in conflicting cases, since pcvt_ioctl.h
gives a hint about the bogus third arg to _IO(). Ifdef the common
typedefs. Export `struct key_t' from pcvt_ioctl.h so pcvt_ioctl.h is
bug for bug compatible with console.h (now both are broken in C++
mode).
1. Takeshi Ohashi <ohashi@atohasi.mickey.ai.kyutech.ac.jp> submitted
code to support bktr_read . /usr/src/share/examples/rgb24.c now works 8)
2. Flemming Jacobsen <fj@schizo.dk.tfs.com> submitted code to support
radio available with in some bt848 based cards;additionally, wrote
code to correctly recognized his bt848 card.
3. Roger Hardiman <roger@cs.strath.ac.uk> submitted various fixes to smooth
out the microcode and made all modes consistent.
4. Added supported for yuv12 so we know can capture raw streams and feed it
to mpeg_encoder . The upshot is that we can now mpeg encode more and save
nearly 100 percent of the disk requirements previously for programs such
as fxtv first save the raw video image to disk then converted to a
format suitable for mpeg_encode.
prematurely when there was a hole (for a cdrom or an unused
interface) in the sequence of wd drives. This caused non-free
wd units to be probed as atapi drives. There was no problem
provided the atapi probe failed correctly.
MUST be PG_BUSY. It is bogus to free a page that isn't busy,
because it is in a state of being "unavailable" when being
freed. The additional advantage is that the page_remove code
has a better cross-check that the page should be busy and
unavailable for other use. There were some minor problems
with the collapse code, and this plugs those subtile "holes."
Also, the vfs_bio code wasn't checking correctly for PG_BUSY
pages. I am going to develop a more consistant scheme for
grabbing pages, busy or otherwise. For now, we are stuck
with the current morass.
- Remove reference to the obsolete options: BOOT_PROBE_KEYBOARD,
BOOT_PROBE_KEYBOARD_LOCK and BOOT_FORCE_COMCONSOLE.
- Add reference to BOOT_COMCONSOLE_SPEED.
If you want to play with it, you can find the final version of the
code in the repository the tag LFS_RETIREMENT.
If somebody makes LFS work again, adding it back is certainly
desireable, but as it is now nobody seems to care much about it,
and it has suffered considerable bitrot since its somewhat haphazard
integration.
R.I.P
available. If there isn't bounce space available, the bounce code
is disabled. This will allow most large systems to run properly
when the bounce space is mistakenly allocated above 16MB.
All known versions of this drive (firmware 21.* and 23.*) will lock up
if presented with a read/write request of > 64 blocks. In the presence
of such a unit, I/O requests of > 64 blocks are fragmented to avoid
this.
6x86MX CPU is enabled (BIOS should not disable it), some BIOS disables
it via CCR4. In this case, cpu variable becomes CPU_486 and
identblue() is called. Because Cyrix 6x86MX has MSR and doesn't have
MSR1002, wrmsr instruction generates general protection fault.
Tested by: Simon Coggins <chaos@ultra.net.au>
This introduce an xxxFS_BOOT for each of the rootable filesystems.
(Presently not required, but encouraged to allow a smooth move of option *FS
to opt_dontuse.h later.)
LFS is temporarily disabled, and will be re-enabled tomorrow.
1) Start using TSM.
Struct procs continue to point to upages structure, after being freed.
Struct vmspace continues to point to pte object and kva space for kstack.
u_map is now superfluous.
2) vm_map's don't need to be reference counted. They always exist either
in the kernel or in a vmspace. The vmspaces are managed by reference
counts.
3) Remove the "wired" vm_map nonsense.
4) No need to keep a cache of kernel stack kva's.
5) Get rid of strange looking ++var, and change to var++.
6) Change more data structures to use our "zone" allocator. Added
struct proc, struct vmspace and struct vnode. This saves a significant
amount of kva space and physical memory. Additionally, this enables
TSM for the zone managed memory.
7) Keep ioopt disabled for now.
8) Remove the now bogus "single use" map concept.
9) Use generation counts or id's for data structures residing in TSM, where
it allows us to avoid unneeded restart overhead during traversals, where
blocking might occur.
10) Account better for memory deficits, so the pageout daemon will be able
to make enough memory available (experimental.)
11) Fix some vnode locking problems. (From Tor, I think.)
12) Add a check in ufs_lookup, to avoid lots of unneeded calls to bcmp.
(experimental.)
13) Significantly shrink, cleanup, and make slightly faster the vm_fault.c
code. Use generation counts, get rid of unneded collpase operations,
and clean up the cluster code.
14) Make vm_zone more suitable for TSM.
This commit is partially as a result of discussions and contributions from
other people, including DG, Tor Egge, PHK, and probably others that I
have forgotten to attribute (so let me know, if I forgot.)
This is not the infamous, final cleanup of the vnode stuff, but a necessary
step. Vnode mgmt should be correct, but things might still change, and
there is still some missing stuff (like ioopt, and physical backing of
non-merged cache files, debugging of layering concepts.)
