From 0556a4b72c6a3617daf174d83d5009bd4b6bf3a0 Mon Sep 17 00:00:00 2001
From: John Spray <jcs@redpanda.com>
Date: Tue, 2 May 2023 11:21:02 +0100
Subject: [PATCH] file: wrap syncfs syscall

It is prudent to syncfs on startup if relying
on all writes from previous instances of one's program
to be persistent.
---
 include/seastar/core/file.hh    |  5 +++++
 include/seastar/core/reactor.hh |  1 +
 src/core/file-impl.hh           |  1 +
 src/core/file.cc                | 13 +++++++++++++
 src/core/reactor.cc             | 10 ++++++++++
 5 files changed, 30 insertions(+)

diff --git a/include/seastar/core/file.hh b/include/seastar/core/file.hh
index 69b976f6cb4..b860af50767 100644
--- a/include/seastar/core/file.hh
+++ b/include/seastar/core/file.hh
@@ -135,6 +135,7 @@ public:
     }
 
     virtual future<> flush(void) = 0;
+    virtual future<> syncfs(void) = 0;
     virtual future<struct stat> stat(void) = 0;
     virtual future<> truncate(uint64_t length) = 0;
     virtual future<> discard(uint64_t offset, uint64_t length) = 0;
@@ -374,6 +375,10 @@ public:
     /// a flush, data is guaranteed to be on disk.
     future<> flush() noexcept;
 
+    /// Causes any dirty data on any file on the same filesystem as this file to
+    /// be flushed to disk.
+    future<> syncfs() noexcept;
+
     /// Returns \c stat information about the file.
     future<struct stat> stat() noexcept;
 
diff --git a/include/seastar/core/reactor.hh b/include/seastar/core/reactor.hh
index a076f411f96..d41f764252a 100644
--- a/include/seastar/core/reactor.hh
+++ b/include/seastar/core/reactor.hh
@@ -685,6 +685,7 @@ private:
 
     future<struct stat> fstat(int fd) noexcept;
     future<struct statfs> fstatfs(int fd) noexcept;
+    future<> syncfs(int fd) noexcept;
     friend future<shared_ptr<file_impl>> make_file_impl(int fd, file_open_options options, int flags) noexcept;
 public:
     future<> readable(pollable_fd_state& fd);
diff --git a/src/core/file-impl.hh b/src/core/file-impl.hh
index 30b5932af94..ffbe5da5028 100644
--- a/src/core/file-impl.hh
+++ b/src/core/file-impl.hh
@@ -90,6 +90,7 @@ protected:
 public:
     virtual ~posix_file_impl() override;
     future<> flush(void) noexcept override;
+    future<> syncfs(void) noexcept override;
     future<struct stat> stat(void) noexcept override;
     future<> truncate(uint64_t length) noexcept override;
     future<> discard(uint64_t offset, uint64_t length) noexcept override;
diff --git a/src/core/file.cc b/src/core/file.cc
index c23b77f3eb8..a23ce311369 100644
--- a/src/core/file.cc
+++ b/src/core/file.cc
@@ -185,6 +185,11 @@ posix_file_impl::flush(void) noexcept {
     return engine().fdatasync(_fd);
 }
 
+future<>
+posix_file_impl::syncfs(void) noexcept {
+    return engine().syncfs(_fd);
+}
+
 future<struct stat>
 posix_file_impl::stat() noexcept {
     return engine().fstat(_fd);
@@ -1220,6 +1225,14 @@ future<> file::flush() noexcept {
   }
 }
 
+future<> file::syncfs() noexcept {
+  try {
+    return _file_impl->syncfs();
+  } catch (...) {
+    return current_exception_as_future();
+  }
+}
+
 future<size_t> file::dma_write(uint64_t pos, std::vector<iovec> iov, const io_priority_class& pc, io_intent* intent) noexcept {
   try {
     return _file_impl->write_dma(pos, std::move(iov), pc, intent);
diff --git a/src/core/reactor.cc b/src/core/reactor.cc
index ae952b1ad79..e333aeed778 100644
--- a/src/core/reactor.cc
+++ b/src/core/reactor.cc
@@ -2225,6 +2225,16 @@ reactor::fstatfs(int fd) noexcept {
     });
 }
 
+future<>
+reactor::syncfs(int fd) noexcept {
+    return _thread_pool->submit<syscall_result<int>>([fd] {
+        auto ret = ::syncfs(fd);
+        return wrap_syscall(ret);
+    }).then([] (syscall_result<int> sr) {
+        sr.throw_if_error();
+    });
+}
+
 future<struct statvfs>
 reactor::statvfs(std::string_view pathname) noexcept {
     // Allocating memory for a sstring can throw, hence the futurize_invoke