Our implementation of granpt(3) could be valid in the future.

When I wrote the pseudo-terminal driver for the MPSAFE TTY code, Robert
Watson and I agreed the best way to implement this, would be to let
posix_openpt() create a pseudo-terminal with proper permissions in place
and let grantpt() and unlockpt() be no-ops.

This isn't valid behaviour when looking at the spec. Because I thought
it was an elegant solution, I filed a bug report at the Austin Group
about this. In their last teleconference, they agreed on this subject.
This means that future revisions of POSIX may allow grantpt() and
unlockpt() to be no-ops if an open() on /dev/ptmx (if the implementation
has such a device) and posix_openpt() already do the right thing.

I'd rather put this in the manpage, because simply mentioning we don't
comply to any standard makes it look worse than it is. Right now we
don't, but at least we took care of it.

Approved by:	re (kib)
MFC after:	3 days

1 files changed, 11 insertions, 15 deletions

diff --git a/lib/libc/stdlib/ptsname.3 b/lib/libc/stdlib/ptsname.3
index bfa3647..f674a54 100644
--- a/lib/libc/stdlib/ptsname.3
+++ b/lib/libc/stdlib/ptsname.3
@@ -134,14 +134,22 @@ The slave pseudo-terminal device could not be accessed.
 The
 .Fn ptsname
 function conforms to
-.St -p1003.1-2001 .
+.St -p1003.1-2008 .
 .Pp
 This implementation of
 .Fn grantpt
 and
 .Fn unlockpt
-does not comply with any standard, because these functions assume the
-pseudo-terminal has the correct attributes upon creation.
+does not conform to
+.St -p1003.1-2008 ,
+because it depends on
+.Xr posix_openpt 2
+to create the pseudo-terminal device with proper permissions in place.
+It only validates whether
+.Fa fildes
+is a valid pseudo-terminal master device.
+Future revisions of the specification will likely allow this behaviour,
+as stated by the Austin Group.
 .Sh HISTORY
 The
 .Fn grantpt ,
@@ -150,15 +158,3 @@ and
 .Fn unlockpt
 functions appeared in
 .Fx 5.0 .
-.Sh NOTES
-The purpose of the
-.Fn grantpt
-and
-.Fn unlockpt
-functions has no meaning in
-.Fx ,
-because pseudo-terminals obtained by
-.Xr posix_openpt 2
-are created on demand.
-Because these devices are created with proper permissions in place, they
-are guaranteed to be unused by unprivileged processes.