Merge pull request #8544 from edolstra/handle-missing-gc-socket

LocalStore: :addTempRoot(): Handle ENOENT
(cherry picked from commit 7115edc85af060ef235ac0270245ab46cc828f7c)
Change-Id: Ie6b1596049c3fde09b98f2f0727899f98e48e6b1

2 files changed, 40 insertions, 20 deletions

diff --git a/src/libstore/gc.cc b/src/libstore/gc.cc
index 7c7273012..ac61f7f53 100644
--- a/src/libstore/gc.cc
+++ b/src/libstore/gc.cc
@@ -142,11 +142,12 @@ void LocalStore::addTempRoot(const StorePath & path)
             try {
                 nix::connect(fdRootsSocket->get(), socketPath);
             } catch (SysError & e) {
-                /* The garbage collector may have exited, so we need to
-                   restart. */
-                if (e.errNo == ECONNREFUSED) {
-                    debug("GC socket connection refused");
+                /* The garbage collector may have exited or not
+                   created the socket yet, so we need to restart. */
+                if (e.errNo == ECONNREFUSED || e.errNo == ENOENT) {
+                    debug("GC socket connection refused: %s", e.msg());
                     fdRootsSocket->close();
+                    std::this_thread::sleep_for(std::chrono::milliseconds(100));
                     goto restart;
                 }
                 throw;
@@ -502,6 +503,11 @@ void LocalStore::collectGarbage(const GCOptions & options, GCResults & results)
     auto fdGCLock = openGCLock();
     FdLock gcLock(fdGCLock.get(), ltWrite, true, "waiting for the big garbage collector lock...");
 
+    /* Synchronisation point to test ENOENT handling in
+       addTempRoot(), see tests/gc-non-blocking.sh. */
+    if (auto p = getEnv("_NIX_TEST_GC_SYNC_1"))
+        readFile(*p);
+
     /* Start the server for receiving new roots. */
     auto socketPath = stateDir.get() + gcSocketPath;
     createDirs(dirOf(socketPath));
@@ -625,6 +631,10 @@ void LocalStore::collectGarbage(const GCOptions & options, GCResults & results)
         roots.insert(root.first);
     }
 
+    /* Synchronisation point for testing, see tests/functional/gc-non-blocking.sh. */
+    if (auto p = getEnv("_NIX_TEST_GC_SYNC_2"))
+        readFile(*p);
+
     /* Helper function that deletes a path from the store and throws
        GCLimitReached if we've deleted enough garbage. */
     auto deleteFromStore = [&](std::string_view baseName)
@@ -771,10 +781,6 @@ void LocalStore::collectGarbage(const GCOptions & options, GCResults & results)
         }
     };
 
-    /* Synchronisation point for testing, see tests/functional/gc-concurrent.sh. */
-    if (auto p = getEnv("_NIX_TEST_GC_SYNC"))
-        readFile(*p);
-
     /* Either delete all garbage paths, or just the specified
        paths (for gcDeleteSpecific). */
     if (options.action == GCOptions::gcDeleteSpecific) {
diff --git a/src/libutil/util.cc b/src/libutil/util.cc
index bbd57434d..6bcb069ba 100644
--- a/src/libutil/util.cc
+++ b/src/libutil/util.cc
@@ -2042,21 +2042,35 @@ void connect(int fd, const std::string & path)
     addr.sun_family = AF_UNIX;
 
     if (path.size() + 1 >= sizeof(addr.sun_path)) {
+        Pipe pipe;
+        pipe.create();
         Pid pid = startProcess([&]() {
-            Path dir = dirOf(path);
-            if (chdir(dir.c_str()) == -1)
-                throw SysError("chdir to '%s' failed", dir);
-            std::string base(baseNameOf(path));
-            if (base.size() + 1 >= sizeof(addr.sun_path))
-                throw Error("socket path '%s' is too long", base);
-            memcpy(addr.sun_path, base.c_str(), base.size() + 1);
-            if (connect(fd, (struct sockaddr *) &addr, sizeof(addr)) == -1)
-                throw SysError("cannot connect to socket at '%s'", path);
-            _exit(0);
+            try {
+                pipe.readSide.close();
+                Path dir = dirOf(path);
+                if (chdir(dir.c_str()) == -1)
+                    throw SysError("chdir to '%s' failed", dir);
+                std::string base(baseNameOf(path));
+                if (base.size() + 1 >= sizeof(addr.sun_path))
+                    throw Error("socket path '%s' is too long", base);
+                memcpy(addr.sun_path, base.c_str(), base.size() + 1);
+                if (connect(fd, (struct sockaddr *) &addr, sizeof(addr)) == -1)
+                    throw SysError("cannot connect to socket at '%s'", path);
+                writeFull(pipe.writeSide.get(), "0\n");
+            } catch (SysError & e) {
+                writeFull(pipe.writeSide.get(), fmt("%d\n", e.errNo));
+            } catch (...) {
+                writeFull(pipe.writeSide.get(), "-1\n");
+            }
         });
-        int status = pid.wait();
-        if (status != 0)
+        pipe.writeSide.close();
+        auto errNo = string2Int<int>(chomp(drainFD(pipe.readSide.get())));
+        if (!errNo || *errNo == -1)
             throw Error("cannot connect to socket at '%s'", path);
+        else if (*errNo > 0) {
+            errno = *errNo;
+            throw SysError("cannot connect to socket at '%s'", path);
+        }
     } else {
         memcpy(addr.sun_path, path.c_str(), path.size() + 1);
         if (connect(fd, (struct sockaddr *) &addr, sizeof(addr)) == -1)