Now that clock_t is an unsigned value, we can also allow the system
uptime to wrap. Essentially, instead of using (a <= b) to see if time
a occurs no later than time b, we use (b - a <= CLOCK_MAX / 2). The
latter value does not exist, so instead we add TMRDIFF_MAX for that
purpose.
We must therefore also avoid using values like 0 and LONG_MAX as
special values for absolute times. This patch extends the libtimers
interface so that it no longer uses 0 to indicate "no timeout".
Similarly, TMR_NEVER is now used as special value only when
otherwise a relative time difference would be used. A minix_timer
structure is now considered in use when it has a watchdog function set,
rather than when the absolute expiry time is not TMR_NEVER. A few new
macros in <minix/timers.h> help with timer comparison and obtaining
properties from a minix_timer structure.
This patch also eliminates the union of timer arguments, instead using
the only union element that is only used (the integer). This prevents
potential problems with e.g. live update. The watchdog function
prototype is changed to pass in the argument value rather than a
pointer to the timer structure, since obtaining the argument value was
the only current use of the timer structure anyway. The result is a
somewhat friendlier timers API.
The VFS select code required a few more invasive changes to restrict
the timer value to the new maximum, effectively matching the timer
code in PM. As a side effect, select(2) has been changed to reject
invalid timeout values. That required a change to the test set, which
relied on the previous, erroneous behavior.
Finally, while we're rewriting significant chunks of the timer code
anyway, also covert it to KNF and add a few more explanatory comments.
Change-Id: Id43165c3fbb140b32b90be2cca7f68dd646ea72e
This patch adds support for Unix98 pseudo terminals, that is,
posix_openpt(3), grantpt(3), unlockpt(3), /dev/ptmx, and /dev/pts/.
The latter is implemented with a new pseudo file system, PTYFS.
In effect, this patch adds secure support for unprivileged pseudo
terminal allocation, allowing programs such as tmux(1) to be used by
non-root users as well. Test77 has been extended with new tests, and
no longer needs to run as root.
The new functionality is optional. To revert to the old behavior,
remove the "ptyfs" entry from /etc/fstab.
Technical nodes:
o The reason for not implementing the NetBSD /dev/ptm approach is that
implementing the corresponding ioctl (TIOCPTMGET) would require
adding a number of extremely hairy exceptions to VFS, including the
PTY driver having to create new file descriptors for its own device
nodes.
o PTYFS is required for Unix98 PTYs in order to avoid that the PTY
driver has to be aware of old-style PTY naming schemes and even has
to call chmod(2) on a disk-backed file system. PTY cannot be its
own PTYFS since a character driver may currently not also be a file
system. However, PTYFS may be subsumed into a DEVFS in the future.
o The Unix98 PTY behavior differs somewhat from NetBSD's, in that
slave nodes are created on ptyfs only upon the first call to
grantpt(3). This approach obviates the need to revoke access as
part of the grantpt(3) call.
o Shutting down PTY may leave slave nodes on PTYFS, but once PTY is
restarted, these leftover slave nodes will be removed before they
create a security risk. Unmounting PTYFS will make existing PTY
slaves permanently unavailable, and absence of PTYFS will block
allocation of new Unix98 PTYs until PTYFS is (re)mounted.
Change-Id: I822b43ba32707c8815fd0f7d5bb7a438f51421c1
