From 114ed1505678640c456533d8e2b4436a52afc7f4 Mon Sep 17 00:00:00 2001 From: наб Date: Tue, 18 Jul 2023 01:31:17 +0200 Subject: grantpt.3: It's a no-op on modern glibc and other UNIXes; HISTORYise MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit FreeBSD, OpenBSD, and Linux (/dev/ptmx) do all intialisation in open(2), and grantpt(3) is a no-op (that checks whether the fd is a pty, except on musl). The illumos gate and NetBSD do a ioctl (and, indeed, illumos-gate commit facf4a8d7b59fde89a8662b4f4c73a758e6c402c ("PSARC/2003/246 Filesystem Driven Device Naming"), which kills pt_chmod, notes that it's been "6464196 bfu should remove pt_chmod, obsoleted by /dev filesystem"). glibc 2.33 completely kills BSD PTY support on Linux (Debian hasn't configured with them on any architecture since 2007: https://bugs.debian.org/338404 and even earlier on some arches; they're really just trivia under Linux ‒ this may be better served stuffed into HISTORY as an explainer for the SIGCHLD thing, since regardless of the "version", the behaviour is well-defined and consistent). There really aren't many cohesive "versions" of this ‒ indeed, so long as grantpt(3) exists it behaves precisely as described here ‒ inasmuch as different systems, historically, had different ptys, and thus different implementations. These are all but trivia. Cc: Jakub Wilk Signed-off-by: Ahelenia Ziemiańska Signed-off-by: Alejandro Colomar --- man3/grantpt.3 | 22 ++++++++++------------ 1 file changed, 10 insertions(+), 12 deletions(-) diff --git a/man3/grantpt.3 b/man3/grantpt.3 index a19172a3e..949f70de9 100644 --- a/man3/grantpt.3 +++ b/man3/grantpt.3 @@ -83,18 +83,6 @@ T} Thread safety MT-Safe locale .hy .ad .sp 1 -.SH VERSIONS -Many systems implement this function via a set-user-ID helper binary -called "pt_chown". -On Linux systems with a devpts filesystem (present since Linux 2.2), -the kernel normally sets the correct ownership and permissions -for the pseudoterminal slave when the master is opened -.RB ( posix_openpt (3)), -so that nothing must be done by -.BR grantpt (). -Thus, no such helper binary is required -(and indeed it is configured to be absent during the -glibc build that is typical on many systems). .SH STANDARDS POSIX.1-2008. .SH HISTORY @@ -103,6 +91,16 @@ POSIX.1-2001. .PP This is part of the UNIX 98 pseudoterminal support, see .BR pts (4). +.PP +Historical systems implemented this function via a set-user-ID helper binary +called "pt_chown". +glibc on Linux before glibc 2.33 could do so as well, +in order to support configurations with only BSD pseudoterminals; +this support has been removed. +On modern systems this is either a no-op +\[em]with permissions configured on pty allocation, as is the case on Linux\[em] +or an +.BR ioctl (2). .SH SEE ALSO .BR open (2), .BR posix_openpt (3), -- cgit v1.2.3