dd: fix handling of 'conv=notrunc seek=N'

Commit e6680912a (dd: create a sparse file when seek=N is used)
broke the use of 'conv=notrunc seek=N' to modify existing files.

Rename seek_sparse() to make_sparse() and:

- add an argument to specify the start of the sparse region;

- call make_sparse() before ftruncate();

- call make_sparse() only if:
  * we can determine the size of the file;
  * the file is not open in append mode;
  * the file is being extended.

This should fix GitHub issue #186.

1 files changed, 1 insertions, 1 deletions

diff --git a/include/mingw.h b/include/mingw.h
index 0fead43c9..39d716521 100644
--- a/include/mingw.h
+++ b/include/mingw.h
@@ -537,5 +537,5 @@ int chdir_system_drive(void);
 char *xabsolute_path(char *path);
 char *get_drive_cwd(const char *path, char *buffer, int size);
 void fix_path_case(char *path);
-void seek_sparse(int fd, size_t size);
+void make_sparse(int fd, off_t start, off_t end);
 int skip_ansi_emulation(int reset);