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
around an output freezing problem (see the CVS log for details). This
is the same approach that sio takes to solve that problem. However,
ucom has a problem that sio doesn't have.
Consider the case where output is pending, and the device is closed.
ttyclose calls tt_close (which indirects to ucomclose) and then calls
ttyflush which calls tt_stop (which indirects to ucomstop). Since
ucomclose removed all the usb transfer points, sc_oxfer will be NULL
when ucomstop calls ucomstart. This results in a null pointer
dereference.
Since calling ucomstart in ucomstart solves other problems, we need to
work with this calling sequence. The easiest way to do that is to
bail early if sc_oxfer is NULL.
Kazuaki ODA-san came up with this patch, and filed a PR. I had seen
this bug at work and this patch does seem to solve it. He had no idea
why it worked, but knew that either this patch, or backing out ucom.c
1.56 fixed his panic. I just did the legwork of chasing down the code
paths that would cause this, and added a comment. This is obscure
enough to warrant a comment, I think.
Submitted by: Kazuaki ODA-san
PR: 113964
Approved by: re (bmah)
s/device_ptr_t/device_t/g
No md5 changes in the .o's
# Note to the md5 tracking club: $FreeBSD$ changes md5 after every commit
# so you need to checkout -kk to get $FreeBSD$ instead of the actual value
# of the keyword.
whether or not the receive pipe is stopped. This ensures that we
do not attempt to start the same transfer twice, and it allows
ucomstop() to skip the restarting of the read pipe if it was not
originally running, such as when called indirectly from ucomreadcb().
PR: kern/79420
MFC after: 1 day
This changes the naming of USB serial devices to: /dev/ttyU%d and
/dev/cuaU%d for call-in and call-out devices respectively. (Please
notice: capital 'U')
Please also note that we now have .init and .lock devices for USB
serial ports. These are not persistent across device removal. devd(8)
can be used to configure them on attachment time.
These changes also improve the chances of the system surviving if
the USB device is unplugged at an inconvenient time. At least we
do not rip things apart while there are any threads in the device
driver anymore.
Remove cdevsw, rely on the tty generic one.
Don't make_dev(), use ttycreate() which does all the magic.
In detach, do close procesing if we ripped things apart
while the device was open. Call ttyfree() once we're done
cleaning up.
future:
rename ttyopen() -> tty_open() and ttyclose() -> tty_close().
We need the ttyopen() and ttyclose() for the new generic cdevsw
functions for tty devices in order to have consistent naming.
copies.
No current line disciplines have a dynamically changing hotchar, and
expecting to receive anything sensible during a change in ldisc is
insane so no locking of the hotchar field is necessary.
called ttyldoptim().
Use this function from all the relevant drivers.
I belive no drivers finger linesw[] directly anymore, paving the way for
locking and refcounting.
Introduce d_version field in struct cdevsw, this must always be
initialized to D_VERSION.
Flip sense of D_NOGIANT flag to D_NEEDGIANT, this involves removing
four D_NOGIANT flags and adding 145 D_NEEDGIANT flags.
Add missing D_TTY flags to various drivers.
Complete asserts that dev_t's passed to ttyread(), ttywrite(),
ttypoll() and ttykqwrite() have (d_flags & D_TTY) and a struct tty
pointer.
Make ttyread(), ttywrite(), ttypoll() and ttykqwrite() the default
cdevsw methods for D_TTY drivers and remove the explicit initializations
in various drivers cdevsw structures.
Free approx 86 major numbers with a mostly automatically generated patch.
A number of strategic drivers have been left behind by caution, and a few
because they still (ab)use their major number.
thread being waken up. The thread waken up can run at a priority as
high as after tsleep().
- Replace selwakeup()s with selwakeuppri()s and pass appropriate
priorities.
- Add cv_broadcastpri() which raises the priority of the broadcast
threads. Used by selwakeuppri() if collision occurs.
Not objected in: -arch, -current
branches:
Initialize struct cdevsw using C99 sparse initializtion and remove
all initializations to default values.
This patch is automatically generated and has been tested by compiling
LINT with all the fields in struct cdevsw in reverse order on alpha,
sparc64 and i386.
Approved by: re(scottl)
debugging levels to off by default. Now that debug levels can be
tweaked by sysctl we don't need to go through hoops to get the
different usb parts to produce debug data.
