dd: create a sparse file when seek=N is used

When the seek=N argument is used mark the file as sparse and set
the range that is sparse.

See https://stackoverflow.com/questions/4011508/how-to-create-a-sparse-file-on-ntfs

1 files changed, 17 insertions, 0 deletions

diff --git a/win32/mingw.c b/win32/mingw.c
index 894388b64..7f8fecdc3 100644
--- a/win32/mingw.c
+++ b/win32/mingw.c
@@ -1750,3 +1750,20 @@ void fix_path_case(char *path)
                 }
         }
 }
+
+void seek_sparse(int fd, size_t size)
+{
+        DWORD dwTemp;
+        HANDLE fh;
+        FILE_ZERO_DATA_INFORMATION fzdi;
+
+        if ((fh=(HANDLE)_get_osfhandle(fd)) == INVALID_HANDLE_VALUE)
+                return;
+
+        DeviceIoControl(fh, FSCTL_SET_SPARSE, NULL, 0, NULL, 0, &dwTemp, NULL);
+
+        fzdi.FileOffset.QuadPart = 0;
+        fzdi.BeyondFinalZero.QuadPart = size;
+        DeviceIoControl(fh, FSCTL_SET_ZERO_DATA, &fzdi, sizeof(fzdi),
+                                         NULL, 0, &dwTemp, NULL);
+}