The last half year I've been working on a replacement TTY layer for the
FreeBSD kernel. The new TTY layer was designed to improve the following:
- Improved driver model:
The old TTY layer has a driver model that is not abstract enough to
make it friendly to use. A good example is the output path, where the
device drivers directly access the output buffers. This means that an
in-kernel PPP implementation must always convert network buffers into
TTY buffers.
If a PPP implementation would be built on top of the new TTY layer
(still needs a hooks layer, though), it would allow the PPP
implementation to directly hand the data to the TTY driver.
- Improved hotplugging:
With the old TTY layer, it isn't entirely safe to destroy TTY's from
the system. This implementation has a two-step destructing design,
where the driver first abandons the TTY. After all threads have left
the TTY, the TTY layer calls a routine in the driver, which can be
used to free resources (unit numbers, etc).
The pts(4) driver also implements this feature, which means
posix_openpt() will now return PTY's that are created on the fly.
- Improved performance:
One of the major improvements is the per-TTY mutex, which is expected
to improve scalability when compared to the old Giant locking.
Another change is the unbuffered copying to userspace, which is both
used on TTY device nodes and PTY masters.
Upgrading should be quite straightforward. Unlike previous versions,
existing kernel configuration files do not need to be changed, except
when they reference device drivers that are listed in UPDATING.
Obtained from: //depot/projects/mpsafetty/...
Approved by: philip (ex-mentor)
Discussed: on the lists, at BSDCan, at the DevSummit
Sponsored by: Snow B.V., the Netherlands
dcons(4) fixed by: kan
o Implement IPI_PREEMPT,
o Set td_lock for the thread being switched out,
o For ULE & SMP, loop while td_lock points to blocked_lock for
the thread being switched in,
o Enable ULE by default in GENERIC and SKI,
an explicit comment that it's needed for the linuxolator. This is not the
case anymore. For all other architectures there was only a "KEEP THIS".
I'm (and other people too) running a COMPAT_43-less kernel since it's not
necessary anymore for the linuxolator. Roman is running such a kernel for a
for longer time. No problems so far. And I doubt other (newer than ia32
or alpha) architectures really depend on it.
This may result in a small performance increase for some workloads.
If the removal of COMPAT_43 results in a not working program, please
recompile it and all dependencies and try again before reporting a
problem.
The only place where COMPAT_43 is needed (as in: does not compile without
it) is in the (outdated/not usable since too old) svr4 code.
Note: this does not remove the COMPAT_43TTY option.
Nagging by: rdivacky
compile option. All FreeBSD packet filters now use the PFIL_HOOKS API and
thus it becomes a standard part of the network stack.
If no hooks are connected the entire packet filter hooks section and related
activities are jumped over. This removes any performance impact if no hooks
are active.
Both OpenBSD and DragonFlyBSD have integrated PFIL_HOOKS permanently as well.
o Fix and improve comments and references,
o Add PFIL_HOOKS, UFS_ACL and UFS_DIRHASH,
o Switch from SCHED_4BSD to SCHED_ULE,
o Remove SCSI_DELAY (there's no SCSI support),
and instead add platform, firmware and EFI stubs to the loader.
The net effect of this change is that besides a special console and
disk driver, the kernel has no knowledge of the simulator. This has
the following advantages:
o Simulator support is much harder to break,
o It's easier to make use of more feature complete simulators.
This would only need a change in the simulator specific loader,
o Running SMP kernels within the simulator. Note that ski at this
time does not simulate IPIs, so there's no way to start APs.
The platform, firmware and EFI stubs describe the following hardware:
o 4 CPU Itanium,
o 128 MB RAM within the 4GB address space,
o 64 MB RAM above the 4GB address space.
NOTE: The stubs in the skiloader describe a machine that should in
parts be defined by the simulator. Things like processor interrupt
block and AP wakeup vector cannot be choosen at random because they
require interpretation by the simulator. Currently the simulator is
ignorant of this.
This change introduces an unofficial SSC call SSC_SAL_SET_VECTORS
which is ignored by the simulator.
Tested with: ski (version 0.943 for linux)
NB: But it will enable it in all kernels not having options "NO_GEOM"
Put the GEOM related options into the intended order.
Add "options NO_GEOM" to all kernel configs apart from NOTES.
In some order of controlled fashion, the NO_GEOM options will be
removed, architecture by architecture in the coming days.
There are currently three known issues which may force people to
need the NO_GEOM option:
boot0cfg/fdisk:
Tries to update the MBR while it is being used to control
slices. GEOM does not allow this as a direct operation.
SCSI floppy drives:
Appearantly the scsi-da driver return "EBUSY" if no media
is inserted. This is wrong, it should return ENXIO.
PC98:
It is unclear if GEOM correctly recognizes all variants of
PC98 disklabels. (Help Wanted! I have neither docs nor HW)
These issues are all being worked.
Sponsored by: DARPA & NAI Labs.
