compate/clipped-write.c: large write(2) fails on Mac OS X/XNU

Due to a bug in the Darwin kernel, write(2) calls have a maximum size
of INT_MAX bytes.

Introduce a new compat function, clipped_write(), that only writes
at most INT_MAX bytes and returns the number of bytes written, as
a substitute for write(2), and allow platforms that need this to
enable it from the build mechanism with NEEDS_CLIPPED_WRITE.

Set it for Mac OS X by default.  It may be necessary to include this
function on Windows, too.

Signed-off-by: Filipe Cabecinhas <filcab+git@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Makefile

@@ -69,6 +69,9 @@ all::
 # Define NO_MSGFMT_EXTENDED_OPTIONS if your implementation of msgfmt
 # doesn't support GNU extensions like --check and --statistics
 #
+# Define NEEDS_CLIPPED_WRITE if your write(2) cannot write more than
+# INT_MAX bytes at once (e.g. MacOS X).
+#
 # Define HAVE_PATHS_H if you have paths.h and want to use the default PATH
 # it specifies.
 #
@@ -1463,6 +1466,11 @@ ifndef NO_MSGFMT_EXTENDED_OPTIONS
 	MSGFMT += --check --statistics
 endif
 
+ifdef NEEDS_CLIPPED_WRITE
+	BASIC_CFLAGS += -DNEEDS_CLIPPED_WRITE
+	COMPAT_OBJS += compat/clipped-write.o
+endif
+
 ifneq (,$(XDL_FAST_HASH))
 	BASIC_CFLAGS += -DXDL_FAST_HASH
 endif

compat/clipped-write.c

@@ -0,0 +1,13 @@
+#include "../git-compat-util.h"
+#undef write
+
+/*
+ * Version of write that will write at most INT_MAX bytes.
+ * Workaround a xnu bug on Mac OS X
+ */
+ssize_t clipped_write(int fildes, const void *buf, size_t nbyte)
+{
+	if (nbyte > INT_MAX)
+		nbyte = INT_MAX;
+	return write(fildes, buf, nbyte);
+}

config.mak.uname

@@ -95,6 +95,7 @@ ifeq ($(uname_S),Darwin)
 	NO_MEMMEM = YesPlease
 	USE_ST_TIMESPEC = YesPlease
 	HAVE_DEV_TTY = YesPlease
+	NEEDS_CLIPPED_WRITE = YesPlease
 	COMPAT_OBJS += compat/precompose_utf8.o
 	BASIC_CFLAGS += -DPRECOMPOSE_UNICODE
 endif

git-compat-util.h

@@ -181,6 +181,11 @@ typedef unsigned long uintptr_t;
 #define probe_utf8_pathname_composition(a,b)
 #endif
 
+#ifdef NEEDS_CLIPPED_WRITE
+ssize_t clipped_write(int fildes, const void *buf, size_t nbyte);
+#define write(x,y,z) clipped_write((x),(y),(z))
+#endif
+
 #ifdef MKDIR_WO_TRAILING_SLASH
 #define mkdir(a,b) compat_mkdir_wo_trailing_slash((a),(b))
 extern int compat_mkdir_wo_trailing_slash(const char*, mode_t);