Implemented sharing datasets via SMB using libshare

Add the initial support for the 'smbshare' option using the
existing libshare infrastructure.  Because this implementation
relies on usershares samba version 3.0.23 is required.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes openzfs#493

lib/libshare/Makefile.am

@@ -7,7 +7,9 @@ DEFAULT_INCLUDES += \
 noinst_LTLIBRARIES = libshare.la
 
 libshare_la_SOURCES = \
+	$(top_srcdir)/lib/libshare/libshare_impl.h \
 	$(top_srcdir)/lib/libshare/libshare.c \
 	$(top_srcdir)/lib/libshare/nfs.c \
-	$(top_srcdir)/lib/libshare/libshare_impl.h \
-	$(top_srcdir)/lib/libshare/nfs.h
+	$(top_srcdir)/lib/libshare/nfs.h \
+	$(top_srcdir)/lib/libshare/smb.c \
+	$(top_srcdir)/lib/libshare/smb.h

lib/libshare/libshare.c

@@ -36,6 +36,7 @@
 #include <libshare.h>
 #include "libshare_impl.h"
 #include "nfs.h"
+#include "smb.h"
 
 static sa_share_impl_t find_share(sa_handle_impl_t handle,
     const char *sharepath);
@@ -103,6 +104,7 @@ __attribute__((constructor)) static void
 libshare_init(void)
 {
 	libshare_nfs_init();
+	libshare_smb_init();
 
 	/*
 	 * This bit causes /etc/dfs/sharetab to be updated before libzfs gets a

lib/libshare/nfs.c

@@ -516,7 +516,7 @@ nfs_validate_shareopts(const char *shareopts)
  * Checks whether a share is currently active.
  */
 static boolean_t
-is_share_active(sa_share_impl_t impl_share)
+nfs_is_share_active(sa_share_impl_t impl_share)
 {
 	char line[512];
 	char *tab, *cur;
@@ -587,7 +587,8 @@ nfs_update_shareopts(sa_share_impl_t impl_share, const char *resource,
 	boolean_t needs_reshare = B_FALSE;
 	char *old_shareopts;
 
-	FSINFO(impl_share, nfs_fstype)->active = is_share_active(impl_share);
+	FSINFO(impl_share, nfs_fstype)->active =
+	    nfs_is_share_active(impl_share);
 
 	old_shareopts = FSINFO(impl_share, nfs_fstype)->shareopts;