link(2): links to directories are refused at the VFS level

Drop the condition that "the caller is the super-user and the file
system ... supports linking to directories."

From nabijaczleweli.

branches: 1.33.10;
Document history
https://www.bell-labs.com/usr/dmr/www/man21.pdf

branches: 1.32.26; 1.32.28;
Add linkat(2) specific errors.

Switch a few remaining system/pathname configuration variables from
"Dv {xxx}" to "Brq Dv xxx".

Revert defective O_SEARCH implementation committed by manu@ along with
the *at system calls on November 18th of last year. Reasons to revert
it include:
- it is incorrect in a whole variety of ways (but fortunately, one
of them is that the missing and improper permission checks have
no net effect);
- it was committed without review or discussion;
- core ruled that all the new O_* flags pertaining to the *at calls
needed to wait until their semantics could be clarified.

manu was asked to revert it on these grounds but has ignored the request.

I have left O_SEARCH defined and visible and made open() explicitly
ignore it. This way, most code that tries to use it will continue to
build and run. I've also arranged lib/libc/c063/t_o_search.c so that
the tests that make use of the O_SEARCH semantics will disappear until
O_SEARCH comes back, and fixed some mistakes and/or incorrect hacks
that were causing some of these to succeed despite the broken O_SEARCH
implementation.

Bump date. New sentence, new line. Wording/articles.

Remove trailing whitespace.

Add most system calls for POSIX extended API set, part 2, with test cases:
faccessat(2), fchmodat(2), fchownat(2), fstatat(2), mkdirat(2), mkfifoat(2),
mknodat(2), linkat(2), readlinkat(2), symlinkat(2), renameat(2), unlinkat(2),
utimensat(2), openat(2).

Also implement O_SEARCH for openat(2)

Still missing:
- some flags for openat(2)
- fexecve(2) implementation

branches: 1.26.2; 1.26.8;
Sort sections. Remove trailing whitespace. Sort errors.
New sentence, new line.

First stage of support for Extended API set 2. Most of the think is
unimplemented, except enough of linkat(2) to hardlink to a symlink.

Everything new in headers is guarded #ifdef _INCOMPLETE_XOPEN_C063 since
some software (e.g.: xcvs in our own tree) will assume they can use openat(2)
when AT_FDCWD is defined. _INCOMPLETE_XOPEN_C063 will go away once support
will be completed.

Consistently use `.Brq Dv XXX' across syscalls man pages, for NAME_MAX
and PATH_MAX.

Remove/convert physical markup.

branches: 1.22.32; 1.22.36;
\- is a minus, not -.

Move UCB-licensed code from 4-clause to 3-clause licence.

Patches provided by Joel Baker in PR 22280, verified by myself.

Use
.In header.h
instead of
.Fd #include \*[Lt]header.h\*[Gt]
Much easier to read and write, and supported by groff for ages.
Okayed by ross.

Merge the nathanw_sa branch.

New sentence, new line. From Robert Elz.

Generate <>& symbolically. I'm avoiding .../dist/... directories for now.

Sort sections, sort SEE ALSO, punctuation and miscellanous fixes.

Boring whitespace fixes.

branches: 1.14.4;
Merge duplicate mentions of EPERM, EACCESS, ... into one entry
(where applicable).

branches: 1.13.2;
Add a LIBRARY section to system call manual pages. While it's clear that the
libraries contain stubs only (with minor exceptions a la pipe(2)), the purpose
of this section is to provide linkage information.

branches: 1.12.6;
Last of the .Os cleanups. .Os is defined in the tmac.doc-common file,
so we shouldn't override it with versions in the manpages. Wheee!

first pass at fixing up capitalization of function names and
arguments; ensure that each is correct with respect to the
implementation, rather than being correct as per english.

Add missing `STANDARDS' compliance statements. As we #define _POSIX_VERSION
to 199009L, bump existing statements to 1003.1-1990.

oops, missed one (from PR 3397)

POSIX.1 specifies that a failed link() to a directory must return EPERM,
and EMLINK was not documented; from Klaus Klein in PR standards/3397.
Also documented EOPNOTSUPP for filesystems that don't support hard links.

merge with lite, keeping most local changes. clean up Ids

Remove description of EINVAL, "The pathname contains a character with the
high-order bit set", as this error is obsolete.

Eventually we may want to add code to some of the "optional" filesystems
(msdosfs, etc.) that checks for illegal characters. At that time it would
be appropriate to reintroduce this error with appropriate text. Perhaps
"The pathname contains a character that is not valid for filesystem type".

Use symbolic names {NAME_MAX} & {PATH_MAX} instead of 255 and 1023 in
description of ENAMETOOLONG error.

Use "Er" for argument to -width in the lists in the ERROR sections --- so
the formatting is consistant.

Clean up manpages:
Use .Fn rather than .Nm macro in HISTORY and STANDARDS sections.
Use .At and .St macros instead of spelling out "Version 6 UNIX",
"IEEE 1003.1-1988 (POSIX)", etc.

Add RCS indentifiers.

branches: 1.1.1;
Initial revision