From dc10c9172e1197c77c246ea75aae63388dcd641e Mon Sep 17 00:00:00 2001
From: Rob Browning <rlb@defaultvalue.org>
Date: Sat, 24 Aug 2019 11:49:54 -0500
Subject: [PATCH] fsck: only specify -t1 when par2 appears to support it

It looks like par2 may reject the "-t1" argument even when it's new
enough to support parallelism, so we can't rely on detecting the
version.  Instead, before running the first real par2 command, test
-t1 in a sandbox to decide whether we can use it.

Signed-off-by: Rob Browning <rlb@defaultvalue.org>
Tested-by: Rob Browning <rlb@defaultvalue.org>
---
 cmd/fsck-cmd.py | 46 +++++++++++++++++++++++++++++++++++-----------
 1 file changed, 35 insertions(+), 11 deletions(-)

diff --git a/cmd/fsck-cmd.py b/cmd/fsck-cmd.py
index 8fc4f7f..8ba698c 100755
--- a/cmd/fsck-cmd.py
+++ b/cmd/fsck-cmd.py
@@ -7,6 +7,9 @@ exec "$bup_python" "$0" ${1+"$@"}
 
 from __future__ import absolute_import, print_function
 import sys, os, glob, subprocess
+from shutil import rmtree
+from subprocess import call
+from tempfile import mkdtemp
 
 from bup import options, git
 from bup.helpers import Sha1, chunkyreader, istty2, log, progress
@@ -42,24 +45,45 @@ def par2_setup():
     else:
         par2_ok = 1
 
-def parv(lvl):
-    if opt.verbose >= lvl:
-        if istty2:
-            return []
-        else:
-            return ['-q']
+def is_par2_parallel():
+    # A true result means it definitely allows -t1; a false result is
+    # technically inconclusive, but likely means no.
+    tmpdir = mkdtemp(prefix="bup-fsck")
+    try:
+        canary = tmpdir + '/canary'
+        with open(canary, 'w') as f:
+            print('canary', file=f)
+        rc = call(('par2', 'create', '-qq', '-t1', canary))
+        return rc == 0
+    finally:
+        rmtree(tmpdir)
+
+_par2_parallel = None
+
+def par2(action, args, verb_floor=0):
+    global _par2_parallel
+    if _par2_parallel is None:
+        _par2_parallel = is_par2_parallel()
+    cmd = ['par2', action]
+    if opt.verbose >= verb_floor and not istty2:
+        cmd.append('-q')
     else:
-        return ['-qq']
+        cmd.append('-qq')
+    if _par2_parallel:
+        cmd.append('-t1')
+    cmd.extend(args)
+    return run(cmd)
 
 def par2_generate(base):
-    return run(['par2', 'create', '-t1', '-n1', '-c200'] + parv(2)
-               + ['--', base, base+'.pack', base+'.idx'])
+    return par2('create',
+                ['-n1', '-c200', '--', base, base + '.pack', base + '.idx'],
+                verb_floor=2)
 
 def par2_verify(base):
-    return run(['par2', 'verify', '-t1'] + parv(3) + ['--', base])
+    return par2('verify', ['--', base], verb_floor=3)
 
 def par2_repair(base):
-    return run(['par2', 'repair', '-t1'] + parv(2) + ['--', base])
+    return par2('repair', ['--', base], verb_floor=2)
 
 def quick_verify(base):
     f = open(base + '.pack', 'rb')
-- 
2.39.2