Allow restores to be run against a read-only repository.

Two things needed to be changed:
1) Don't open a log file when log-level-file=off
2) New --no-lock option to suppress lock file creation for restores.

doc/xml/change-log.xml

@@ -9,7 +9,7 @@
         <changelog-release date="XXXX-XX-XX" version="0.90" title="UNDER DEVELOPMENT">
             <release-feature-bullet-list>
                 <release-feature>
-                    <text></text>
+                    <text>Allow restores to be performed on a read-only repository by using <setting>--no-lock</setting> and <setting>--log-level-file=off</setting>.  The <setting>--no-lock</setting> option can only be used with restores.</text>
                 </release-feature>
             </release-feature-bullet-list>
         </changelog-release>

doc/xml/reference.xml

@@ -594,6 +594,15 @@
                         <example>y</example>
                     </option>
 
+                    <!-- OPERATION - RESTORE COMMAND - LOCK OPTION -->
+                    <option id="lock" name="Lock">
+                        <summary>Create a lock so restores on a stanza cannot run simultaneously.</summary>
+
+                        <text>Locking during restores is enabled by default but can be disabled using --no-lock.  Be <i>very</i> careful when disabling this option because simultaneous restores to a single path might result in a corrupt cluster.</text>
+
+                        <example>--no-lock</example>
+                    </option>
+
                     <!-- OPERATION - RESTORE COMMAND - TYPE OPTION -->
                     <option id="type" name="Type">
                         <summary>Recovery type.</summary>

lib/BackRest/Common/Lock.pm

@@ -105,6 +105,12 @@ sub lockAcquire
             {name => 'iProcessIdx', required => false}
         );
 
+    my $bResult = true;
+
+    # Acquire if locking is enabled
+    if (!optionTest(OPTION_LOCK) || optionGet(OPTION_LOCK))
+    {
+        $bResult = false;
         my $strRepoPath = optionGet(OPTION_REPO_PATH);
 
         # Cannot proceed if a lock is currently held
@@ -126,8 +132,6 @@ sub lockAcquire
             or confess &log(ERROR, "unable to open lock file ${strCurrentLockFile}", ERROR_FILE_OPEN);
 
         # Attempt to lock the lock file
-    my $bResult = false;
-
         if (!flock($hCurrentLockHandle, LOCK_EX | LOCK_NB))
         {
             close($hCurrentLockHandle);
@@ -149,6 +153,7 @@ sub lockAcquire
             # Lock was successful
             $bResult = true;
         }
+    }
 
     # Return from function and log return values if any
     return logDebugReturn
@@ -177,6 +182,9 @@ sub lockRelease
             {name => 'bFailOnNoLock', default => true}
         );
 
+    # Release if locking is enabled
+    if (!optionTest(OPTION_LOCK) || optionGet(OPTION_LOCK))
+    {
         # Fail if there is no lock
         if (!defined($strCurrentLockType))
         {
@@ -201,6 +209,7 @@ sub lockRelease
             undef($strCurrentLockType);
             undef($hCurrentLockHandle);
         }
+    }
 
     # Return from function and log return values if any
     logDebugReturn($strOperation);

lib/BackRest/Common/Log.pm

@@ -99,6 +99,9 @@ sub logFileSet
 {
     my $strFile = shift;
 
+    # Only open the log file if file logging is enabled
+    if ($strLogLevelFile ne OFF)
+    {
         unless (-e dirname($strFile))
         {
             mkdir(dirname($strFile), oct('0770'))
@@ -122,6 +125,7 @@ sub logFileSet
         }
 
         syswrite($hLogFile, "-------------------PROCESS START-------------------\n");
+    }
 }
 
 push @EXPORT, qw(logFileSet);

lib/BackRest/Config/Config.pm

@@ -218,6 +218,8 @@ use constant OPTION_TYPE                                            => 'type';
     push @EXPORT, qw(OPTION_TYPE);
 use constant OPTION_OUTPUT                                          => 'output';
     push @EXPORT, qw(OPTION_OUTPUT);
+use constant OPTION_LOCK                                            => 'lock';
+    push @EXPORT, qw(OPTION_LOCK);
 
 # Command-line only help/version
 #-----------------------------------------------------------------------------------------------------------------------------------
@@ -363,6 +365,8 @@ use constant OPTION_DEFAULT_RESTORE_TARGET_RESUME                   => false;
     push @EXPORT, qw(OPTION_DEFAULT_RESTORE_TARGET_RESUME);
 use constant OPTION_DEFAULT_RESTORE_TYPE                            => RECOVERY_TYPE_DEFAULT;
     push @EXPORT, qw(OPTION_DEFAULT_RESTORE_TYPE);
+use constant OPTION_DEFAULT_LOCK                                    => true;
+    push @EXPORT, qw(OPTION_DEFAULT_LOCK);
 
 # Command-line only test
 #-----------------------------------------------------------------------------------------------------------------------------------
@@ -545,6 +549,17 @@ my %oOptionRule =
         }
     },
 
+    &OPTION_LOCK =>
+    {
+        &OPTION_RULE_TYPE => OPTION_TYPE_BOOLEAN,
+        &OPTION_RULE_DEFAULT => OPTION_DEFAULT_LOCK,
+        &OPTION_RULE_NEGATE => true,
+        &OPTION_RULE_COMMAND =>
+        {
+            &CMD_RESTORE => true
+        }
+    },
+
     &OPTION_NO_START_STOP =>
     {
         &OPTION_RULE_TYPE => OPTION_TYPE_BOOLEAN,

lib/BackRest/Config/ConfigHelpData.pm

@@ -853,6 +853,18 @@ my $oConfigHelpData =
                             "combination with --delta a timestamp/size delta will be performed instead of using checksums."
                 },
 
+                # LOCK Option Help
+                #-------------------------------------------------------------------------------------------------------------------
+                'lock' =>
+                {
+                    summary =>
+                        "Create a lock so restores on a stanza cannot run simultaneously.",
+                    description =>
+                        "Locking during restores is enabled by default but can be disabled using --no-lock. Be very careful " .
+                            "when disabling this option because simultaneous restores to a single path might result in a " .
+                            "corrupt cluster."
+                },
+
                 'log-level-console' => 'section',
                 'log-level-file' => 'section',
                 'neutral-umask' => 'section',