From e6680912a298dc2dee83f41837cb52160cf562d9 Mon Sep 17 00:00:00 2001
From: Ron Yorston <rmy@pobox.com>
Date: Tue, 24 Mar 2020 16:37:13 +0000
Subject: 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
---
 coreutils/dd.c  |  3 +++
 include/mingw.h |  1 +
 win32/mingw.c   | 17 +++++++++++++++++
 3 files changed, 21 insertions(+)

diff --git a/coreutils/dd.c b/coreutils/dd.c
index 3054ec6ea..fc8b1dbb2 100644
--- a/coreutils/dd.c
+++ b/coreutils/dd.c
@@ -502,6 +502,9 @@ int dd_main(int argc UNUSED_PARAM, char **argv)
 	}
 	if (seek) {
 		size_t blocksz = (G.flags & FLAG_SEEK_BYTES) ? 1 : obs;
+#if ENABLE_PLATFORM_MINGW32
+		seek_sparse(ofd, seek * blocksz);
+#endif
 		if (lseek(ofd, seek * blocksz, SEEK_CUR) < 0)
 			goto die_outfile;
 	}
diff --git a/include/mingw.h b/include/mingw.h
index 3ab49a920..a5a84cff2 100644
--- a/include/mingw.h
+++ b/include/mingw.h
@@ -533,3 +533,4 @@ 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);
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);
+}
-- 
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