Make dbufstat work on FreeBSD

With procfs_list kstats implemented for FreeBSD, dbufs are now exposed
as kstat.zfs.misc.dbufs.

On FreeBSD, dbufstats can use the sysctl instead of procfs when no
input file has been given.

Enable the dbufstats tests on FreeBSD.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Ryan Moeller <freqlabs@FreeBSD.org>
Closes #11008

cmd/dbufstat/dbufstat.in

@@ -113,6 +113,21 @@ cmd = ("Usage: dbufstat [-bdhnrtvx] [-i file] [-f fields] [-o file] "
 raw = 0
 
 
+if sys.platform.startswith("freebsd"):
+    import io
+    # Requires py-sysctl on FreeBSD
+    import sysctl
+
+    def default_ifile():
+        dbufs = sysctl.filter("kstat.zfs.misc.dbufs")[0].value
+        sys.stdin = io.StringIO(dbufs)
+        return "-"
+
+elif sys.platform.startswith("linux"):
+    def default_ifile():
+        return "/proc/spl/kstat/zfs/dbufs"
+
+
 def print_incompat_helper(incompat):
     cnt = 0
     for key in sorted(incompat):
@@ -645,7 +660,7 @@ def main():
             sys.exit(1)
 
     if not ifile:
-        ifile = '/proc/spl/kstat/zfs/dbufs'
+        ifile = default_ifile()
 
     if ifile is not "-":
         try: