and for all (I hope). Packages such as wine, JDK, and linuxthreads
should no longer have any problems with re-entering the dynamic
linker.
This commit replaces the locking used in the dynamic linker with a
new spinlock-based reader/writer lock implementation. Brian
Fundakowski Feldman <green> argued for this from the very beginning,
but it took me a long time to come around to his point of view.
Spinlocks are the only kinds of locks that work with all thread
packages. But on uniprocessor systems they can be inefficient,
because while a contender for the lock is spinning the holder of the
lock cannot make any progress toward releasing it. To alleviate
this disadvantage I have borrowed a trick from Sleepycat's Berkeley
DB implementation. When spinning for a lock, the requester does a
nanosleep() call for 1 usec. each time around the loop. This will
generally yield the CPU to other threads, allowing the lock holder
to finish its business and release the lock. I chose 1 usec. as the
minimum sleep which would with reasonable certainty not be rounded
down to 0.
The formerly machine-independent file "lockdflt.c" has been moved
into the architecture-specific subdirectories by repository copy.
It now contains the machine-dependent spinlocking code. For the
spinlocks I used the very nifty "simple, non-scalable reader-preference
lock" which I found at
<http://www.cs.rochester.edu/u/scott/synchronization/pseudocode/rw.html>
on all CPUs except the 80386 (the specific CPU model, not the
architecture). The 80386 CPU doesn't support the necessary "cmpxchg"
instruction, so on that CPU a simple exclusive test-and-set lock
is used instead. 80386 CPUs are detected at initialization time by
trying to execute "cmpxchg" and catching the resulting SIGILL
signal.
To reduce contention for the locks, I have revamped a couple of
key data structures, permitting all common operations to be done
under non-exclusive (reader) locking. The only operations that
require exclusive locking now are the rare intrusive operations
such as dlopen() and dlclose().
The dllockinit() interface is now deprecated. It still exists,
but only as a do-nothing stub. I plan to remove it as soon as is
reasonably possible. (From the very beginning it was clearly
labeled as experimental and subject to change.) As far as I know,
only the linuxthreads port uses dllockinit(). This interface turned
out to have several problems. As one example, when the dynamic
linker called a client-supplied locking function, that function
sometimes needed lazy binding, causing re-entry into the dynamic
linker and a big looping mess. And in any case, it turned out to be
too burdensome to require threads packages to register themselves
with the dynamic linker.
"ld-elf.so.1.old". The dynamic linker is a critical component of
the system, and it is difficult to recover if it is damaged and
there isn't a working backup available. For instance, parts of
the toolchain such as the assembler are dynamically linked, making
it impossible to build a new dynamic linker if the installed one
doesn't work.
terminal emulator.
As pointed out by jhb, a more scalable solution would be preferable
when multiple applications in the base system begin linking against
libh.
Submitted by: Doug Barton <DougB@gorean.org>
o If the new ``filter-decapsulation'' is enabled, delve into UDP packets
that contain 0xff 0x03 as the first two bytes, and if we recognise it
as PROTO_IP, decapsulate it for the purpose of filter checking.
If we recognise it as PROTO_<anything else> mention this for logging
purposes only.
This change is aimed at people running PPPoUDP where the UDP traffic is
being sent over another PPP link. It's desireable to have the top level
link connected all the time, but to have the bottom level link capable
of decapsulating the traffic and comparing the payload against the filters,
thus allowing ``set filter dial ...'' to work in tunnelled environments.
The caveat here is that the top ppp cannot employ any compression layers
without making the data unreadable for the bottom ppp. ``disable deflate
pred1 vj'' and ``deny deflate pred1 vj'' is suggested.
use a CHAR_MIN-based array, like elsewhere in the code.
Remove a number of unused variables (some due to the above change, one
that was left after a number of optimizing steps through the source).
Brucified by: bde
July 4th due to the new sys/modules/sound/drivers/* being added to the
tree. You will need to do this until you do a make installworld with
my bsd.kmod.mk change.
remove (comment out) functions defined or depricated elsewhere:
bsearch, lfind, lsearch, insque, remque
change hcreate to take a size_t rather than uint (essentially the same)
since hcreate/hdestroy are now in <search.h>, remove private search.h
in lib/libc/db/hash/
add $FreeBSD tags to hsearch.c
