Spin-off syscall-related file operations (#78)

* [file_utils] spin-off syscall-related file operations

1. Eliminate the potential circular dependency between
   persistent-data/block.h and persistent-data/file_utils.h,
   if the former one wants to include the latter.
2. Avoid namespace pollution by removing the "using namespace std"
   declaration in block.tcc.
3. Correct the header hierarchy: base/xml_utils.h now no longer
   depends on the higher-level persistent-data/file_utils.h

* [file_utils] support block files in get_file_length()

thin-provisioning/cache_stream.cc

@@ -2,25 +2,14 @@
 #include "thin-provisioning/cache_stream.h"
 #include "persistent-data/file_utils.h"
 
+#include <fcntl.h>
+
 using namespace thin_provisioning;
 using namespace std;
 using namespace persistent_data;
 
 //----------------------------------------------------------------
 
-namespace {
-	int open_file(string const &path) {
-		int fd = ::open(path.c_str(), O_RDONLY | O_DIRECT | O_EXCL, 0666);
-		if (fd < 0)
-			syscall_failed("open",
-				       "Note: you cannot run this tool with these options on live metadata.");
-
-		return fd;
-	}
-}
-
-//----------------------------------------------------------------
-
 cache_stream::cache_stream(string const &path,
 			   block_address block_size,
 			   size_t cache_mem)
@@ -29,7 +18,7 @@ cache_stream::cache_stream(string const &path,
 
 	  // hack because cache uses LRU rather than MRU
 	  cache_blocks_((cache_mem / block_size) / 2u),
-	  fd_(open_file(path)),
+	  fd_(file_utils::open_file(path, O_RDONLY | O_EXCL)),
 	  v_(new bcache::noop_validator()),
 	  cache_(new block_cache(fd_, block_size / 512, nr_blocks_, cache_mem)),
 	  current_index_(0) {

thin-provisioning/superblock.cc

@@ -3,8 +3,11 @@
 #include "thin-provisioning/superblock.h"
 #include "persistent-data/file_utils.h"
 
+#include <sstream>
+
 using namespace thin_provisioning;
 using namespace superblock_detail;
+using namespace std;
 
 //----------------------------------------------------------------
 

thin-provisioning/thin_trim.cc

@@ -1,8 +1,10 @@
 #include <iostream>
 #include <getopt.h>
 #include <sys/ioctl.h>
+#include <sys/stat.h>
 #include <linux/fs.h>
 #include <libgen.h>
+#include <fcntl.h>
 
 #undef BLOCK_SIZE