From 04170d06bf7d17f882c01d3ab98885e0f3e46d2f Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <eelco.dolstra@logicblox.com>
Date: Thu, 10 Jul 2014 11:51:22 +0200
Subject: nix-copy-closure: Fix race condition
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There is a long-standing race condition when copying a closure to a
remote machine, particularly affecting build-remote.pl: the client
first asks the remote machine which paths it already has, then copies
over the missing paths. If the garbage collector kicks in on the
remote machine between the first and second step, the already-present
paths may be deleted. The missing paths may then refer to deleted
paths, causing nix-copy-closure to fail. The client now performs both
steps using a single remote Nix call (using ‘nix-store --serve’),
locking all paths in the closure while querying.

I changed the --serve protocol a bit (getting rid of QueryCommand), so
this breaks the SSH substituter from older versions. But it was marked
experimental anyway.

Fixes #141.
---
 src/download-via-ssh/download-via-ssh.cc | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

(limited to 'src/download-via-ssh')

diff --git a/src/download-via-ssh/download-via-ssh.cc b/src/download-via-ssh/download-via-ssh.cc
index 6361e71e9927..6cbcd9891cf2 100644
--- a/src/download-via-ssh/download-via-ssh.cc
+++ b/src/download-via-ssh/download-via-ssh.cc
@@ -58,7 +58,7 @@ static std::pair<FdSink, FdSource> connect(const string & conn)
 
 static void substitute(std::pair<FdSink, FdSource> & pipes, Path storePath, Path destPath)
 {
-    writeInt(cmdSubstitute, pipes.first);
+    writeInt(cmdDumpStorePath, pipes.first);
     writeString(storePath, pipes.first);
     pipes.first.flush();
     restorePath(destPath, pipes.second);
@@ -68,20 +68,20 @@ static void substitute(std::pair<FdSink, FdSource> & pipes, Path storePath, Path
 
 static void query(std::pair<FdSink, FdSource> & pipes)
 {
-    writeInt(cmdQuery, pipes.first);
     for (string line; getline(std::cin, line);) {
         Strings tokenized = tokenizeString<Strings>(line);
         string cmd = tokenized.front();
         tokenized.pop_front();
         if (cmd == "have") {
-            writeInt(qCmdHave, pipes.first);
+            writeInt(cmdQueryValidPaths, pipes.first);
+            writeInt(0, pipes.first); // don't lock
             writeStrings(tokenized, pipes.first);
             pipes.first.flush();
             PathSet paths = readStrings<PathSet>(pipes.second);
             foreach (PathSet::iterator, i, paths)
                 std::cout << *i << std::endl;
         } else if (cmd == "info") {
-            writeInt(qCmdInfo, pipes.first);
+            writeInt(cmdQueryPathInfos, pipes.first);
             writeStrings(tokenized, pipes.first);
             pipes.first.flush();
             while (1) {
-- 
cgit 1.4.1