Persist the in-progress checkout pid

Summary:
The in-progress checkout pid was always serialized to the snapshot
file, but we ignored it when reading the file. Let's read it and keep it in
memory. This will be used by the next diff to determine if the in progress
checkout is resumable or not.

Reviewed By: xavierd

Differential Revision: D37006722

fbshipit-source-id: 2fa374b309eda36e280bcd352abdaf03193d167e

eden/fs/config/CheckoutConfig.cpp

@@ -167,8 +167,7 @@ ParentCommit CheckoutConfig::getParentCommit() const {
     }
 
     case kSnapshotFormatCheckoutInProgressVersion: {
-      // Skip the PID
-      cursor.skip(sizeof(uint32_t));
+      auto pid = cursor.readBE<int32_t>();
 
       auto fromLength = cursor.readBE<uint32_t>();
       std::string fromRootId = cursor.readFixedString(fromLength);
@@ -177,7 +176,7 @@ ParentCommit CheckoutConfig::getParentCommit() const {
       std::string toRootId = cursor.readFixedString(toLength);
 
       return ParentCommit::CheckoutInProgress{
-          RootId{std::move(fromRootId)}, RootId{std::move(toRootId)}};
+          RootId{std::move(fromRootId)}, RootId{std::move(toRootId)}, pid};
     }
 
     case kSnapshotFormatWorkingCopyParentAndCheckedOutRevisionVersion: {

eden/fs/config/ParentCommit.cpp

@@ -14,6 +14,21 @@ bool ParentCommit::isCheckoutInProgress() const {
   return std::holds_alternative<ParentCommit::CheckoutInProgress>(state_);
 }
 
+std::optional<pid_t> ParentCommit::getInProgressPid() const {
+  return std::visit(
+      [](auto&& state) -> std::optional<pid_t> {
+        using StateType = std::decay_t<decltype(state)>;
+        if constexpr (std::is_same_v<
+                          StateType,
+                          WorkingCopyParentAndCheckedOutRevision>) {
+          return std::nullopt;
+        } else {
+          return state.pid;
+        }
+      },
+      state_);
+}
+
 std::optional<RootId> ParentCommit::getLastCheckoutId(
     RootIdPreference preference) const {
   return std::visit(

eden/fs/config/ParentCommit.h

@@ -33,6 +33,11 @@ class ParentCommit {
    */
   bool isCheckoutInProgress() const;
 
+  /**
+   * Returns the pid of the process currently doing a checkout.
+   */
+  std::optional<pid_t> getInProgressPid() const;
+
   /**
    * Since the parent commit might contain multiple RootId, allows chosing
    * which one should be preferred.
@@ -68,6 +73,7 @@ class ParentCommit {
   struct CheckoutInProgress {
     RootId from;
     RootId to;
+    pid_t pid;
   };
 
   /**

eden/fs/config/test/CheckoutConfigTest.cpp

@@ -162,7 +162,8 @@ TEST_F(CheckoutConfigTest, testInProgress) {
 
   ParentCommit inProgress = ParentCommit::CheckoutInProgress{
       RootId{"99887766554433221100aabbccddeeffabcdef99"},
-      RootId{"fedcba99887766554433221100ffeeddccbbaa99"}};
+      RootId{"fedcba99887766554433221100ffeeddccbbaa99"},
+      123};
 
   auto parent = config->getParentCommit();
   EXPECT_EQ(inProgress, parent);
@@ -174,7 +175,7 @@ TEST_F(CheckoutConfigTest, testInProgressRoundtrip) {
 
   auto from = RootId{"99887766554433221100aabbccddeeffabcdef99"};
   auto to = RootId{"fedcba998887766554433221100ffeeddccbbaa99"};
-  ParentCommit inProgress = ParentCommit::CheckoutInProgress{from, to};
+  ParentCommit inProgress = ParentCommit::CheckoutInProgress{from, to, 123};
 
   config->setCheckoutInProgress(from, to);
 

eden/fs/inodes/EdenMount.cpp

@@ -292,7 +292,8 @@ FOLLY_NODISCARD folly::Future<folly::Unit> EdenMount::initialize(
                   checkoutOriginalDest = parentCommit.getLastCheckoutId(
                       ParentCommit::RootIdPreference::To),
                   checkoutOriginalSrc = parentCommit.getLastCheckoutId(
-                      ParentCommit::RootIdPreference::From)](
+                      ParentCommit::RootIdPreference::From),
+                  checkoutPid = parentCommit.getInProgressPid()](
                      std::shared_ptr<const Tree> parentTree) mutable {
         std::optional<std::tuple<RootId, RootId>> originalCheckoutTrees =
             std::nullopt;
@@ -305,7 +306,9 @@ FOLLY_NODISCARD folly::Future<folly::Unit> EdenMount::initialize(
             parentTree,
             workingCopyParentRootId,
             inProgressCheckout,
-            originalCheckoutTrees};
+            originalCheckoutTrees,
+            checkoutPid,
+        };
 
         // Record the transition from no snapshot to the current snapshot in
         // the journal.  This also sets things up so that we can carry the

eden/fs/inodes/EdenMount.h

@@ -1155,6 +1155,7 @@ class EdenMount : public std::enable_shared_from_this<EdenMount> {
     RootId workingCopyParentRootId;
     bool checkoutInProgress = false;
     std::optional<std::tuple<RootId, RootId>> checkoutOriginalTrees;
+    std::optional<pid_t> checkoutPid;
   };
 
   /**