diff --git a/persistent-data/block.h b/persistent-data/block.h
index d463083..c472d9d 100644
--- a/persistent-data/block.h
+++ b/persistent-data/block.h
@@ -85,6 +85,7 @@ namespace persistent_data {
 		enum mode {
 			READ_ONLY,
 			READ_WRITE,
+			CREATE
 		};
 
 		block_io(std::string const &path, block_address nr_blocks, mode m);
diff --git a/persistent-data/block.tcc b/persistent-data/block.tcc
index a7faae3..1571650 100644
--- a/persistent-data/block.tcc
+++ b/persistent-data/block.tcc
@@ -23,6 +23,8 @@
 #include <sys/stat.h>
 #include <sys/types.h>
 #include <unistd.h>
+#include <fcntl.h>
+#include <string.h>
 
 #include <boost/bind.hpp>
 #include <stdexcept>
@@ -35,37 +37,102 @@ using namespace std;
 
 //----------------------------------------------------------------
 
+namespace {
+	using namespace std;
+
+	int const DEFAULT_MODE = 0666;
+	int const OPEN_FLAGS = O_DIRECT | O_SYNC;
+
+	// FIXME: introduce a new exception for this, or at least lift this
+	// to exception.h
+	void syscall_failed(char const *call) {
+		char buffer[128];
+		char *msg = strerror_r(errno, buffer, sizeof(buffer));
+
+		ostringstream out;
+		out << "syscall '" << call << "' failed: " << msg;
+		throw runtime_error(out.str());
+	}
+
+	int open_file(string const &path, int flags) {
+		int fd = ::open(path.c_str(), OPEN_FLAGS | flags, DEFAULT_MODE);
+		if (fd < 0)
+			syscall_failed("open");
+
+		return fd;
+	}
+
+	bool file_exists(string const &path) {
+		typename ::stat info;
+
+		int r = ::stat(path.c_str(), &info);
+		if (r) {
+			if (errno == ENOENT)
+				return false;
+
+			syscall_failed("stat");
+			return false; // never get here
+
+		} else
+			return S_ISREG(info.st_mode) || S_ISBLK(info.st_mode);
+	}
+
+	int create_block_file(string const &path, off_t file_size) {
+		if (file_exists(path)) {
+			ostringstream out;
+			out << __FUNCTION__ << ": file '" << path << "' already exists";
+			throw runtime_error(out.str());
+		}
+
+		int fd = open_file(path, O_CREAT | O_RDWR);
+		int r = ::fallocate(fd, 0, 0, file_size);
+		if (r < 0)
+			syscall_failed("fallocate");
+
+		return fd;
+	}
+
+	int open_block_file(string const &path, off_t min_size, bool writeable) {
+		if (!file_exists(path)) {
+			ostringstream out;
+			out << __FUNCTION__ << ": file '" << path << "' doesn't exist";
+			throw runtime_error(out.str());
+		}
+
+		return open_file(path, writeable ? O_RDWR : O_RDONLY);
+	}
+};
+
 template <uint32_t BlockSize>
 block_io<BlockSize>::block_io(std::string const &path, block_address nr_blocks, mode m)
 	: nr_blocks_(nr_blocks),
 	  mode_(m)
 {
-	int fd_mode = O_DIRECT | O_SYNC;
+	off_t file_size = nr_blocks * BlockSize;
 
 	switch (m) {
 	case READ_ONLY:
-		fd_mode |= O_RDONLY;
+		fd_ = open_block_file(path, file_size, false);
 		break;
 
 	case READ_WRITE:
-		fd_mode |= O_RDWR;
+		fd_ = open_block_file(path, file_size, true);
+		break;
+
+	case CREATE:
+		fd_ = create_block_file(path, file_size);
 		break;
 
 	default:
 		throw runtime_error("unsupported mode");
-		break;
 	}
-
-	// fd_ = ::open(path.c_str(), writeable ? (O_RDWR | O_CREAT) : O_RDONLY, 0666);
-	fd_ = ::open(path.c_str(), fd_mode, 0666);
-	if (fd_ < 0)
-		throw std::runtime_error("couldn't open file");
 }
 
 template <uint32_t BlockSize>
 block_io<BlockSize>::~block_io()
 {
-	::close(fd_);
+	if (::close(fd_) < 0)
+		syscall_failed("close");
 }
 
 template <uint32_t BlockSize>
diff --git a/unit-tests/block_t.cc b/unit-tests/block_t.cc
index 7a1d7c1..bce0988 100644
--- a/unit-tests/block_t.cc
+++ b/unit-tests/block_t.cc
@@ -29,7 +29,8 @@ namespace {
 	unsigned const MAX_HELD_LOCKS = 16;
 
 	block_manager<4096>::ptr create_bm(block_address nr = 1024) {
-		return block_manager<4096>::ptr(new block_manager<4096>("./test.data", nr, MAX_HELD_LOCKS, true));
+		return block_manager<4096>::ptr(
+			new block_manager<4096>("./test.data", nr, MAX_HELD_LOCKS, block_io<>::READ_WRITE));
 	}
 
 	template <uint32_t BlockSize>
@@ -61,7 +62,8 @@ namespace {
 
 BOOST_AUTO_TEST_CASE(bad_path)
 {
-	BOOST_CHECK_THROW(bm4096("/bogus/bogus/bogus", 1234, 4), runtime_error);
+	BOOST_CHECK_THROW(bm4096("/bogus/bogus/bogus", 1234, 4, block_io<>::READ_WRITE),
+			  runtime_error);
 }
 
 BOOST_AUTO_TEST_CASE(out_of_range_access)
@@ -110,13 +112,13 @@ BOOST_AUTO_TEST_CASE(write_lock_zero_zeroes)
 BOOST_AUTO_TEST_CASE(different_block_sizes)
 {
 	{
-		bm4096 bm("./test.data", 64, 1);
+		bm4096 bm("./test.data", 64, 1, block_io<>::READ_WRITE);
 		bm4096::read_ref rr = bm.read_lock(0);
 		BOOST_CHECK_EQUAL(sizeof(rr.data()), 4096);
 	}
 
 	{
-		block_manager<64 * 1024> bm("./test.data", 64, true);
+		block_manager<64 * 1024> bm("./test.data", 64, 1, block_io<64 * 1024>::READ_WRITE);
 		block_manager<64 * 1024>::read_ref rr = bm.read_lock(0);
 		BOOST_CHECK_EQUAL(sizeof(rr.data()), 64 * 1024);
 	}