Copy stable/10@r272459 to releng/10.1 as part of
the 10.1-RELEASE process.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Don't print the nmount(2) provided error message if it is empty.

Change mount_fs() to not exit on error. The "failok" mount option
requires that errors are passed to the caller.

PR: 163668
Reviewed by: Garrett Cooper

Change checkpath() to not exit on error. This is a prerequisite for
fixing the mount(8) "failok" option.

PR: 163668
Reviewed by: Garrett Cooper, delphij (previous version)

Add missing static keywords for global variables to tools in sbin/.

These tools declare global variables without using the static keyword,
even though their use is limited to a single C-file, or without placing
an extern declaration of them in the proper header file.

Remove the advertising clause from UCB copyrighted files in sbin. This
is in accordance with the information at
ftp://ftp.cs.berkeley.edu/pub/4bsd/README.Impt.License.Change

Be a little bit more pestimistic in argument handling - check if we've
overflown our internal buffer (though after the fact), and s/strncpy/strlcpy/

Reviewed by: rodrigc
Obtained from: Juniper Networks

Pass a char buffer parameter with name "errmsg" to nmount().
For filesystems which use vfs_mount_error() to log an error, this
char buffer will be populated with a string error message.
If nmount() fails, in addition to printing out strerror(errno),
print out the "errmsg" populated by vfs_mount_error().

- Make size parameter to build_iovec() a size_t, not an int
- Add build_iovec_argf() helper function, for help converting old
mount options which used the mount_argf() function for the mount() syscall.

Discussed with: phk

- Minor fixes to raise WARNS level to 6.
- Teach the mount program to call the nmount() syscall directly
- Preserve existing method of calling mount() for UFS, until we clean things
up.
- Preserve existing method of forking and calling external mount programs for
mfs, msdosfs, nfs, nfs4, ntfs, nwfs, nullfs, portalfs, reiserfs, smbfs,
udf, umapfs, unionfs
- devfs, linprocfs, procfs, ext2fs call nmount() syscall directly, since
that is all those external mount programs were doing

Reviewed by: phk
Discussed on: arch