From 12b949525df1aba390ec6c2bcfb406bbcf6a8df5 Mon Sep 17 00:00:00 2001
From: Marcus Holland-Moritz <github@mhxnet.de>
Date: Fri, 5 Mar 2021 22:42:45 +0100
Subject: [PATCH] Add asynchronous `readv` method for filesystem_v2

---
 include/dwarfs/filesystem_v2.h   |  9 +++++++
 include/dwarfs/inode_reader_v2.h |  9 +++++++
 src/dwarfs/filesystem_v2.cpp     | 17 ++++++++++---
 src/dwarfs/inode_reader_v2.cpp   | 42 +++++++++++++++++++++++---------
 4 files changed, 62 insertions(+), 15 deletions(-)

diff --git a/include/dwarfs/filesystem_v2.h b/include/dwarfs/filesystem_v2.h
index 62b013c3..18067171 100644
--- a/include/dwarfs/filesystem_v2.h
+++ b/include/dwarfs/filesystem_v2.h
@@ -24,6 +24,7 @@
 #include <cstddef>
 #include <cstdint>
 #include <functional>
+#include <future>
 #include <iosfwd>
 #include <memory>
 #include <optional>
@@ -47,6 +48,7 @@ struct filesystem_options;
 struct rewrite_options;
 struct iovec_read_buf;
 
+class block_range;
 class filesystem_writer;
 class logger;
 class mmif;
@@ -146,6 +148,11 @@ class filesystem_v2 {
     return impl_->readv(inode, buf, size, offset);
   }
 
+  folly::Expected<std::vector<std::future<block_range>>, int>
+  readv(uint32_t inode, size_t size, off_t offset) const {
+    return impl_->readv(inode, size, offset);
+  }
+
   class impl {
    public:
     virtual ~impl() = default;
@@ -180,6 +187,8 @@ class filesystem_v2 {
     read(uint32_t inode, char* buf, size_t size, off_t offset) const = 0;
     virtual ssize_t readv(uint32_t inode, iovec_read_buf& buf, size_t size,
                           off_t offset) const = 0;
+    virtual folly::Expected<std::vector<std::future<block_range>>, int>
+    readv(uint32_t inode, size_t size, off_t offset) const = 0;
   };
 
  private:
diff --git a/include/dwarfs/inode_reader_v2.h b/include/dwarfs/inode_reader_v2.h
index 48d3d62f..07578731 100644
--- a/include/dwarfs/inode_reader_v2.h
+++ b/include/dwarfs/inode_reader_v2.h
@@ -28,6 +28,8 @@
 
 #include <sys/types.h>
 
+#include <folly/Expected.h>
+
 #include "dwarfs/metadata_types.h"
 
 namespace dwarfs {
@@ -53,6 +55,11 @@ class inode_reader_v2 {
     return impl_->readv(buf, size, offset, chunks);
   }
 
+  folly::Expected<std::vector<std::future<block_range>>, int>
+  readv(size_t size, off_t offset, chunk_range chunks) const {
+    return impl_->readv(size, offset, chunks);
+  }
+
   void
   dump(std::ostream& os, const std::string& indent, chunk_range chunks) const {
     impl_->dump(os, indent, chunks);
@@ -66,6 +73,8 @@ class inode_reader_v2 {
     read(char* buf, size_t size, off_t offset, chunk_range chunks) const = 0;
     virtual ssize_t readv(iovec_read_buf& buf, size_t size, off_t offset,
                           chunk_range chunks) const = 0;
+    virtual folly::Expected<std::vector<std::future<block_range>>, int>
+    readv(size_t size, off_t offset, chunk_range chunks) const = 0;
     virtual void dump(std::ostream& os, const std::string& indent,
                       chunk_range chunks) const = 0;
   };
diff --git a/src/dwarfs/filesystem_v2.cpp b/src/dwarfs/filesystem_v2.cpp
index 688df457..fd0adac6 100644
--- a/src/dwarfs/filesystem_v2.cpp
+++ b/src/dwarfs/filesystem_v2.cpp
@@ -21,7 +21,6 @@
 
 #include <cstddef>
 #include <cstring>
-#include <optional>
 #include <unordered_map>
 #include <vector>
 
@@ -209,6 +208,8 @@ class filesystem_ : public filesystem_v2::impl {
   read(uint32_t inode, char* buf, size_t size, off_t offset) const override;
   ssize_t readv(uint32_t inode, iovec_read_buf& buf, size_t size,
                 off_t offset) const override;
+  folly::Expected<std::vector<std::future<block_range>>, int>
+  readv(uint32_t inode, size_t size, off_t offset) const override;
 
  private:
   LOG_PROXY_DECL(LoggerPolicy);
@@ -382,7 +383,7 @@ ssize_t filesystem_<LoggerPolicy>::read(uint32_t inode, char* buf, size_t size,
   if (auto chunks = meta_.get_chunks(inode)) {
     return ir_.read(buf, size, offset, *chunks);
   }
-  return -1;
+  return -EBADF;
 }
 
 template <typename LoggerPolicy>
@@ -391,7 +392,17 @@ ssize_t filesystem_<LoggerPolicy>::readv(uint32_t inode, iovec_read_buf& buf,
   if (auto chunks = meta_.get_chunks(inode)) {
     return ir_.readv(buf, size, offset, *chunks);
   }
-  return -1;
+  return -EBADF;
+}
+
+template <typename LoggerPolicy>
+folly::Expected<std::vector<std::future<block_range>>, int>
+filesystem_<LoggerPolicy>::readv(uint32_t inode, size_t size,
+                                 off_t offset) const {
+  if (auto chunks = meta_.get_chunks(inode)) {
+    return ir_.readv(size, offset, *chunks);
+  }
+  return folly::makeUnexpected(-EBADF);
 }
 
 } // namespace
diff --git a/src/dwarfs/inode_reader_v2.cpp b/src/dwarfs/inode_reader_v2.cpp
index 2bdbbcdd..056f13db 100644
--- a/src/dwarfs/inode_reader_v2.cpp
+++ b/src/dwarfs/inode_reader_v2.cpp
@@ -64,10 +64,15 @@ class inode_reader_ : public inode_reader_v2::impl {
   read(char* buf, size_t size, off_t offset, chunk_range chunks) const override;
   ssize_t readv(iovec_read_buf& buf, size_t size, off_t offset,
                 chunk_range chunks) const override;
+  folly::Expected<std::vector<std::future<block_range>>, int>
+  readv(size_t size, off_t offset, chunk_range chunks) const override;
   void dump(std::ostream& os, const std::string& indent,
             chunk_range chunks) const override;
 
  private:
+  folly::Expected<std::vector<std::future<block_range>>, int>
+  read(size_t size, off_t offset, chunk_range chunks) const;
+
   template <typename StoreFunc>
   ssize_t read(size_t size, off_t offset, chunk_range chunks,
                const StoreFunc& store) const;
@@ -89,16 +94,18 @@ void inode_reader_<LoggerPolicy>::dump(std::ostream& os,
 }
 
 template <typename LoggerPolicy>
-template <typename StoreFunc>
-ssize_t
-inode_reader_<LoggerPolicy>::read(size_t size, off_t offset, chunk_range chunks,
-                                  const StoreFunc& store) const {
+folly::Expected<std::vector<std::future<block_range>>, int>
+inode_reader_<LoggerPolicy>::readv(size_t size, off_t offset,
+                                   chunk_range chunks) const {
   if (offset < 0) {
-    return -EINVAL;
+    return folly::makeUnexpected(-EINVAL);
   }
 
+  // request ranges from block cache
+  std::vector<std::future<block_range>> ranges;
+
   if (size == 0 || chunks.empty()) {
-    return 0;
+    return ranges;
   }
 
   auto it = chunks.begin();
@@ -118,19 +125,16 @@ inode_reader_<LoggerPolicy>::read(size_t size, off_t offset, chunk_range chunks,
 
   if (it == end) {
     // offset beyond EOF; TODO: check if this should rather be -EINVAL
-    return 0;
+    return ranges;
   }
 
-  // request ranges from block cache
-  std::vector<std::future<block_range>> ranges;
-
   for (size_t num_read = 0; it != end && num_read < size; ++it) {
     size_t chunksize = it->size() - offset;
     size_t chunkoff = it->offset() + offset;
 
     if (chunksize == 0) {
       LOG_ERROR << "invalid zero-sized chunk";
-      return -EIO;
+      return folly::makeUnexpected(-EIO);
     }
 
     if (num_read + chunksize > size) {
@@ -143,10 +147,24 @@ inode_reader_<LoggerPolicy>::read(size_t size, off_t offset, chunk_range chunks,
     offset = 0;
   }
 
+  return ranges;
+}
+
+template <typename LoggerPolicy>
+template <typename StoreFunc>
+ssize_t
+inode_reader_<LoggerPolicy>::read(size_t size, off_t offset, chunk_range chunks,
+                                  const StoreFunc& store) const {
+  auto ranges = readv(size, offset, chunks);
+
+  if (!ranges) {
+    return ranges.error();
+  }
+
   try {
     // now fill the buffer
     size_t num_read = 0;
-    for (auto& r : ranges) {
+    for (auto& r : ranges.value()) {
       auto br = r.get();
       store(num_read, br);
       num_read += br.size();