From 0d5f85b255e68385b4aa1b6b8c40ab4b7ad35125 Mon Sep 17 00:00:00 2001
From: Ron Yorston <rmy@pobox.com>
Date: Tue, 24 May 2016 10:48:34 +0100
Subject: win32: return an error when lseek is applied to a pipe

tail failed to process input from a pipe correctly:

   $ echo -n 54321 | tail -c 3
   543

It was trying to use lseek as an optimisation but WIN32 lseek doesn't
return an error whan applied to a pipe.  Fix this by providing a wrapper
for lseek.
---
 include/mingw.h |  7 ++++---
 win32/mingw.c   | 14 ++++++++++++++
 2 files changed, 18 insertions(+), 3 deletions(-)

diff --git a/include/mingw.h b/include/mingw.h
index efb17e137..04700963c 100644
--- a/include/mingw.h
+++ b/include/mingw.h
@@ -289,11 +289,9 @@ int mingw_chmod(const char *path, int mode);
 #define mkdir mingw_mkdir
 #define chmod mingw_chmod
 
-#if ENABLE_LFS
+#if ENABLE_LFS && !defined(__MINGW64_VERSION_MAJOR)
 # define off_t off64_t
 #endif
-#undef lseek
-#define lseek _lseeki64
 
 typedef int nlink_t;
 typedef int blksize_t;
@@ -388,6 +386,7 @@ NOIMPL(chroot,const char *root UNUSED_PARAM);
 NOIMPL(fchdir,int fd UNUSED_PARAM);
 int mingw_dup2 (int fd, int fdto);
 char *mingw_getcwd(char *pointer, int len);
+off_t mingw_lseek(int fd, off_t offset, int whence);
 
 
 IMPL(getgid,int,DEFAULT_GID,void);
@@ -428,6 +427,8 @@ int mingw_rmdir(const char *name);
 #define open mingw_open
 #define unlink mingw_unlink
 #define rmdir mingw_rmdir
+#undef lseek
+#define lseek mingw_lseek
 
 #undef access
 #define access mingw_access
diff --git a/win32/mingw.c b/win32/mingw.c
index ebdcdee26..23ca5d3dd 100644
--- a/win32/mingw.c
+++ b/win32/mingw.c
@@ -1030,3 +1030,17 @@ DIR *mingw_opendir(const char *path)
 
 	return opendir(path);
 }
+
+off_t mingw_lseek(int fd, off_t offset, int whence)
+{
+	HANDLE h = (HANDLE)_get_osfhandle(fd);
+	if (h == INVALID_HANDLE_VALUE) {
+		errno = EBADF;
+		return -1;
+	}
+	if (GetFileType(h) != FILE_TYPE_DISK) {
+		errno = ESPIPE;
+		return -1;
+	}
+	return _lseeki64(fd, offset, whence);
+}
-- 
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