Just like the old TTY layer, the current MPSAFE TTY layer does not make
any attempt to serialize calls of write(). Data is copied into the
kernel in 256 (TTY_STACKBUF) byte chunks. If a write() call occurs at
the same time, the data may interleave. This is especially likely when
the TTY starts blocking, because the output queue reaches the high
watermark.
I've implemented this by adding a new flag, TTY_BUSY_OUT, which is used
to mark a TTY as having a thread stuck in write(). Because I don't want
non-blocking processes to be possibly blocked by a sleeping thread, I'm
still allowing it to bypass the protection. According to this message,
the Linux kernel returns EAGAIN in such cases, but I think that's a
little too restrictive:
http://kerneltrap.org/index.php?q=mailarchive/linux-kernel/2007/5/2/85418/thread
PR: kern/118287
When we leave the console TTY constantly open, we never reset the
termios attributes. This causes output processing, echoing, etc. not to
be reset to the proper values when going into single user mode after the
system has booted. It also causes nl-to-crnl-conversion not to take
place during shutdown, which causes a `staircase effect'.
This patch adds a new TTY flag, TF_OPENED_CONS, which is set when the
TTY is opened through /dev/console. Because the flags are only used by
the kernel and the pstat(8) utility, I've decided to renumber the TTY
flags. This shouldn't be an issue, because the TTY layer is not yet part
of a stable release.
Reported by: Mark Atkinson <atkin901 yahoo com>
Tested by: sepotvin
One of the features that prevented us from fixing some of the TTY
consumers to work once again, was an interface that allowed consumers to
do the following:
- `Sniff' incoming data, which is used by the snp(4) driver.
- Take direct control of the input and output paths of a TTY, which is
used by ng_tty(4), ppp(4), sl(4), etc.
There's no practical advantage in committing a hooks layer without
having any consumers. In P4 there is a preliminary port of snp(4) and
thompsa@ is busy porting ng_tty(4) to this interface. I already want to
have it in the tree, because this may stimulate others to work on the
remaining modules.
Discussed with: thompsa
Obtained from: //depot/projects/mpsafetty/...
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
format, with humanize_number(3).
- Move the common parts of the code that prints the sizes for a single
swap device and the total to a single function to avoid repeating
the humanize_number() stuff all over the place.
- Change the type of CONVERT() from intmax_t to int64_t, since this
makes calling humanize_number() easier but cast the values to
intmax_t before printing them, to make use of the %jd format that
printf() supports.
- Document the new -h flag in the manpage and bump its date.
Approved by: pjd
Useful tips: brooks
MFC after: 2 weeks
to be the same as -ragged in the current implementation) to
-ragged. With mdocNG, -filled displays produce the correct
output, formatted and justified to both margins.
Remove the old description in favour of the new description which lists the
-M and -N flags along with all the other flags. This is consistent with the
manual pages for ps, netstat, iostat, etc.
This will make a number of things easier in the future, as well as (finally!)
avoiding the Id-smashing problem which has plagued developers for so long.
Boy, I'm glad we're not using sup anymore. This update would have been
insane otherwise.
