variant symlinks (was Re: Anybody working on removing sendmail from base?)

[John]

I've had variant (magic) symlinks working under 4-stable for awhile
now. You can do some really neat stuff with them.

An old message concerning them can be found on the -stable
list, msgid <20030810040807.GA26220 at xxxxxxxxxxx>.

An older set of patches can be seen here:

http://people.freebsd.org/~jwd/mlinks/freebsd-magic-patches
http://people.freebsd.org/~jwd/mlinks/env-magic-patches

What you want requires both sets. It also requires some
patches to the shells to make sure the environment variables
are all handled in a known fashion.

I have some newer patch sets I need to upload.

The origin of the patchset comes from an old netbsd pr.

-John



%mount
/dev/ad0s1a on / (ufs, NFS exported, local, magiclinks)

cd /
ls -ald clstr
lrwxr-xr-x  1 root  wheel  25 Oct  3 11:09 tst -> /clstr/@env_CLSTR/clstr

man mount

   magiclinks
           Expand special strings (beginning with ``@'') when
           traversing symbolic links.  See symlink(7) for a list of
           supported strings.


man 7 symlink

MAGIC SYMLINKS
     Symlinks in file systems with the MNT_MAGICLINKS flag set have ``magic''
     patterns in symlinks expanded.  Those patterns begin with ``@'' (an at-
     sign), and end at the end of the pathname component (i.e. at the next
     ``/'', or at the end of the symbolic link if there are no more slashes).
     The following patterns are supported:

     @domainname    Expands to the machine's domain name, as set by
                    setdomainname(3).

     @env_XXXXX     Expands to the current setting of the environment variable
                    XXXXX

     @hostname      Expands to the machine's host name, as set by
                    sethostname(3).

     @kernel_ident  Expands to the name of the config(8) file used to generate
                    the running kernel.

     @machine       Expands to the value of MACHINE for the system (also, the
                    same as make(1) 's ${MACHINE} variable).

     @machine_arch  Expands to the value of MACHINE_ARCH for the system (also,
                    the same as make(1) 's ${MACHINE_ARCH} variable).

     @osrelease     Expands to the operating system release of the running
                    kernel.

     @ostype        Expands to the operating system type of the running ker-
                    nel.  (This will always be ``NetBSD'' for NetBSD systems.)