Support using Linux page cache for reads

src/blockstore_disk.cpp

@@ -45,6 +45,13 @@ void blockstore_disk_t::parse_config(std::map<std::string, std::string> & config
     meta_block_size = parse_size(config["meta_block_size"]);
     bitmap_granularity = parse_size(config["bitmap_granularity"]);
     meta_format = stoull_full(config["meta_format"]);
+    cached_read_data = config["cached_read_data"] == "true" || config["cached_read_data"] == "yes" || config["cached_read_data"] == "1";
+    cached_read_meta = cached_read_data && (meta_device == data_device || meta_device == "") &&
+        config.find("cached_read_meta") == config.end() ||
+        config["cached_read_meta"] == "true" || config["cached_read_meta"] == "yes" || config["cached_read_meta"] == "1";
+    cached_read_journal = cached_read_meta && (journal_device == meta_device || journal_device == "") &&
+        config.find("cached_read_journal") == config.end() ||
+        config["cached_read_journal"] == "true" || config["cached_read_journal"] == "yes" || config["cached_read_journal"] == "1";
     if (config["data_csum_type"] == "crc32c")
     {
         data_csum_type = BLOCKSTORE_CSUM_CRC32C;
@@ -288,6 +295,18 @@ void blockstore_disk_t::open_data()
     {
         throw std::runtime_error(std::string("Failed to lock data device: ") + strerror(errno));
     }
+    if (cached_read_data)
+    {
+        read_data_fd = open(data_device.c_str(), O_RDWR);
+        if (read_data_fd == -1)
+        {
+            throw std::runtime_error("Failed to open data device "+data_device+": "+std::string(strerror(errno)));
+        }
+    }
+    else
+    {
+        read_data_fd = data_fd;
+    }
 }
 
 void blockstore_disk_t::open_meta()
@@ -308,6 +327,18 @@ void blockstore_disk_t::open_meta()
         {
             throw std::runtime_error(std::string("Failed to lock metadata device: ") + strerror(errno));
         }
+        if (cached_read_meta)
+        {
+            read_meta_fd = open(meta_device.c_str(), O_RDWR);
+            if (read_meta_fd == -1)
+            {
+                throw std::runtime_error("Failed to open metadata device "+meta_device+": "+std::string(strerror(errno)));
+            }
+        }
+        else
+        {
+            read_meta_fd = meta_fd;
+        }
     }
     else
     {
@@ -326,6 +357,22 @@ void blockstore_disk_t::open_meta()
             ") is not a multiple of data device sector size ("+std::to_string(meta_device_sect)+")"
         );
     }
+    if (!cached_read_meta)
+    {
+        read_meta_fd = meta_fd;
+    }
+    else if (meta_device == data_device && cached_read_data)
+    {
+        read_meta_fd = read_data_fd;
+    }
+    else
+    {
+        read_meta_fd = open(meta_device.c_str(), O_RDWR);
+        if (read_meta_fd == -1)
+        {
+            throw std::runtime_error("Failed to open metadata device "+meta_device+": "+std::string(strerror(errno)));
+        }
+    }
 }
 
 void blockstore_disk_t::open_journal()
@@ -360,6 +407,26 @@ void blockstore_disk_t::open_journal()
             ") is not a multiple of journal device sector size ("+std::to_string(journal_device_sect)+")"
         );
     }
+    if (!cached_read_journal)
+    {
+        read_journal_fd = journal_fd;
+    }
+    else if (journal_device == meta_device && cached_read_meta)
+    {
+        read_journal_fd = read_meta_fd;
+    }
+    else if (journal_device == data_device && cached_read_data)
+    {
+        read_journal_fd = read_data_fd;
+    }
+    else
+    {
+        read_journal_fd = open(journal_device.c_str(), O_RDWR);
+        if (read_journal_fd == -1)
+        {
+            throw std::runtime_error("Failed to open journal device "+journal_device+": "+std::string(strerror(errno)));
+        }
+    }
 }
 
 void blockstore_disk_t::close_all()
@@ -370,5 +437,12 @@ void blockstore_disk_t::close_all()
         close(meta_fd);
     if (journal_fd >= 0 && journal_fd != meta_fd)
         close(journal_fd);
+    if (read_data_fd >= 0 && read_data_fd != data_fd)
+        close(read_data_fd);
+    if (read_meta_fd >= 0 && read_meta_fd != meta_fd)
+        close(read_meta_fd);
+    if (read_journal_fd >= 0 && read_journal_fd != journal_fd)
+        close(read_journal_fd);
     data_fd = meta_fd = journal_fd = -1;
+    read_data_fd = read_meta_fd = read_journal_fd = -1;
 }