From 034f59bbb9a8c6a5febfed042fa9119410a3f123 Mon Sep 17 00:00:00 2001
From: Raito Bezarius <raito@lix.systems>
Date: Wed, 26 Mar 2025 01:06:03 +0100
Subject: [PATCH] libutil: writeFile variant for file descriptors

`writeFile` lose its `sync` boolean flag to make things simpler.

A new `writeFileAndSync` function is created and all call sites are
converted to it.

Change-Id: Ib871a5283a9c047db1e4fe48a241506e4aab9192
Signed-off-by: Raito Bezarius <raito@lix.systems>
---
 src/libstore/local-store.cc                 |  4 +--
 src/libutil/file-system.cc                  | 35 ++++++++++++++++-----
 src/libutil/include/nix/util/file-system.hh | 13 ++++++--
 3 files changed, 39 insertions(+), 13 deletions(-)

diff --git a/src/libstore/local-store.cc b/src/libstore/local-store.cc
index e53cab2dc..00c1ac6dd 100644
--- a/src/libstore/local-store.cc
+++ b/src/libstore/local-store.cc
@@ -247,7 +247,7 @@ LocalStore::LocalStore(ref<const Config> config)
     else if (curSchema == 0) { /* new store */
         curSchema = nixSchemaVersion;
         openDB(*state, true);
-        writeFile(schemaPath, fmt("%1%", curSchema), 0666, true);
+        writeFileAndSync(schemaPath, fmt("%1%", curSchema), 0666);
     }
 
     else if (curSchema < nixSchemaVersion) {
@@ -298,7 +298,7 @@ LocalStore::LocalStore(ref<const Config> config)
             txn.commit();
         }
 
-        writeFile(schemaPath, fmt("%1%", nixSchemaVersion), 0666, true);
+        writeFileAndSync(schemaPath, fmt("%1%", nixSchemaVersion), 0666);
 
         lockFile(globalLock.get(), ltRead, true);
     }
diff --git a/src/libutil/file-system.cc b/src/libutil/file-system.cc
index fee2945ff..4c3a56e65 100644
--- a/src/libutil/file-system.cc
+++ b/src/libutil/file-system.cc
@@ -304,7 +304,7 @@ void readFile(const Path & path, Sink & sink, bool memory_map)
 }
 
 
-void writeFile(const Path & path, std::string_view s, mode_t mode, bool sync)
+void writeFile(const Path & path, std::string_view s, mode_t mode)
 {
     AutoCloseFD fd = toDescriptor(open(path.c_str(), O_WRONLY | O_TRUNC | O_CREAT
 // TODO
@@ -314,20 +314,39 @@ void writeFile(const Path & path, std::string_view s, mode_t mode, bool sync)
        , mode));
     if (!fd)
         throw SysError("opening file '%1%'", path);
+
+    writeFile(fd, s, mode);
+
+    /* Close explicitly to propagate the exceptions. */
+    fd.close();
+}
+
+void writeFile(AutoCloseFD & fd, std::string_view s, mode_t mode)
+{
+    assert(fd);
     try {
         writeFull(fd.get(), s);
     } catch (Error & e) {
-        e.addTrace({}, "writing file '%1%'", path);
+        e.addTrace({}, "writing file '%1%'", fd.guessOrInventPath());
         throw;
     }
-    if (sync)
-        fd.fsync();
-    // Explicitly close to make sure exceptions are propagated.
-    fd.close();
-    if (sync)
-        syncParent(path);
 }
 
+void writeFileAndSync(const Path & path, std::string_view s, mode_t mode)
+{
+    {
+        AutoCloseFD fd{open(path.c_str(), O_WRONLY | O_TRUNC | O_CREAT | O_CLOEXEC, mode)};
+        if (!fd)
+            throw SysError("opening file '%1%'", path);
+
+        writeFile(fd, s, mode);
+        fd.fsync();
+        /* Close explicitly to ensure that exceptions are propagated. */
+        fd.close();
+    }
+
+    syncParent(path);
+}
 
 void writeFile(const Path & path, Source & source, mode_t mode, bool sync)
 {
diff --git a/src/libutil/include/nix/util/file-system.hh b/src/libutil/include/nix/util/file-system.hh
index 0121745ab..77d5f2aa1 100644
--- a/src/libutil/include/nix/util/file-system.hh
+++ b/src/libutil/include/nix/util/file-system.hh
@@ -172,10 +172,10 @@ void readFile(const Path & path, Sink & sink, bool memory_map = true);
 /**
  * Write a string to a file.
  */
-void writeFile(const Path & path, std::string_view s, mode_t mode = 0666, bool sync = false);
-static inline void writeFile(const std::filesystem::path & path, std::string_view s, mode_t mode = 0666, bool sync = false)
+void writeFile(const Path & path, std::string_view s, mode_t mode = 0666);
+static inline void writeFile(const std::filesystem::path & path, std::string_view s, mode_t mode = 0666)
 {
-    return writeFile(path.string(), s, mode, sync);
+    return writeFile(path.string(), s, mode);
 }
 
 void writeFile(const Path & path, Source & source, mode_t mode = 0666, bool sync = false);
@@ -184,6 +184,13 @@ static inline void writeFile(const std::filesystem::path & path, Source & source
     return writeFile(path.string(), source, mode, sync);
 }
 
+void writeFile(AutoCloseFD & fd, std::string_view s, mode_t mode = 0666 );
+
+/**
+ * Write a string to a file and flush the file and its parents direcotry to disk.
+ */
+void writeFileAndSync(const Path & path, std::string_view s, mode_t mode = 0666);
+
 /**
  * Flush a path's parent directory to disk.
  */