Re: write() _will_ fail on Mac OS X/XNU if nbytes > INT_MAX

From: Filipe Cabecinhas <filcab@gmail.com>
Date: May 10, 2013, 22:24 UTC
Message-ID: <CAEDE8507jPW4sKW7-xX5-+3YpFgfzkXzeskCNRrD7T6ynxgdNA@mail.gmail.com>
In-Reply-To: <7vbo8j600q.fsf@alter.siamese.dyndns.org>

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

This patch introduces a new compat function: clipped_write This function behaves the same as write() but will write, at most, INT_MAX characters. It may be necessary to include this function on Windows, too.

Signed-off-by: Filipe Cabecinhas <filcab+git@gmail.com>
---
 Makefile               |  5 +++++
 compat/clipped-write.c | 13 +++++++++++++
 config.mak.uname       |  1 +
 git-compat-util.h      |  5 +++++
 4 files changed, 24 insertions(+)
 create mode 100644 compat/clipped-write.c

diff --git a/Makefile b/Makefile
index 0f931a2..ccb8f3f 100644
--- a/Makefile
+++ b/Makefile
@@ -1466,6 +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 (,$(XDL_FAST_HASH))
  BASIC_CFLAGS += -DXDL_FAST_HASH
 endif
diff --git a/compat/clipped-write.c b/compat/clipped-write.c
new file mode 100644
index 0000000..9183698
--- /dev/null
+++ b/compat/clipped-write.c
@@ -0,0 +1,13 @@
+#include <limits.h>
+#include <unistd.h>
+
+/*
+ * Version of write that will write at most INT_MAX bytes.
+ * Workaround a xnu bug on Mac OS X
+ */
+ssize_t clipped_write(int fildes, const void *buf, size_t nbyte)
+{
+ if (nbyte > INT_MAX)
+ nbyte = INT_MAX;
+ return write(fildes, buf, nbyte);
+}
diff --git a/config.mak.uname b/config.mak.uname
index d78fd3d..174703b 100644
--- a/config.mak.uname
+++ b/config.mak.uname
@@ -95,6 +95,7 @@ ifeq ($(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
diff --git a/git-compat-util.h b/git-compat-util.h
index e955bb5..a96db23 100644
--- a/git-compat-util.h
+++ b/git-compat-util.h
@@ -185,6 +185,11 @@ int get_st_mode_bits(const char *path, int *mode);
 #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);
--
1.8.2.1.343.g13c32df