From a983e6ac58094a3b2466ad3be13049ce213f9fc3 Mon Sep 17 00:00:00 2001 From: Junio C Hamano Date: Wed, 11 Feb 2015 13:13:10 -0800 Subject: [PATCH] xread/xwrite: clip MAX_IO_SIZE to SSIZE_MAX MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit Since 0b6806b9 (xread, xwrite: limit size of IO to 8MB, 2013-08-20), we chomp our calls to read(2) and write(2) into chunks of MAX_IO_SIZE bytes (8 MiB), because a large IO results in a bad latency when the program needs to be killed. This also brought our IO below SSIZE_MAX, which is a limit POSIX allows read(2) and write(2) to fail when the IO size exceeds it, for OS X, where a problem was originally reported. However, there are other systems that define SSIZE_MAX smaller than our default, and feeding 8 MiB to underlying read(2)/write(2) would fail. Make sure we clip our calls to the lower limit as well. Reported-by: Joachim Schmitz Helped-by: Torsten Bögershausen Helped-by: Eric Sunshine Signed-off-by: Junio C Hamano --- wrapper.c | 16 +++++++++++++++- 1 file changed, 15 insertions(+), 1 deletion(-) diff --git a/wrapper.c b/wrapper.c index f92b147598..cfaf23d387 100644 --- a/wrapper.c +++ b/wrapper.c @@ -135,8 +135,22 @@ void *xcalloc(size_t nmemb, size_t size) * 64-bit is buggy, returning EINVAL if len >= INT_MAX; and even in * the absense of bugs, large chunks can result in bad latencies when * you decide to kill the process. + * + * We pick 8 MiB as our default, but if the platform defines SSIZE_MAX + * that is smaller than that, clip it to SSIZE_MAX, as a call to + * read(2) or write(2) larger than that is allowed to fail. As the last + * resort, we allow a port to pass via CFLAGS e.g. "-DMAX_IO_SIZE=value" + * to override this, if the definition of SSIZE_MAX given by the platform + * is broken. */ -#define MAX_IO_SIZE (8*1024*1024) +#ifndef MAX_IO_SIZE +# define MAX_IO_SIZE_DEFAULT (8*1024*1024) +# if defined(SSIZE_MAX) && (SSIZE_MAX < MAX_IO_SIZE_DEFAULT) +# define MAX_IO_SIZE SSIZE_MAX +# else +# define MAX_IO_SIZE MAX_IO_SIZE_DEFAULT +# endif +#endif /* * xread() is the same a read(), but it automatically restarts read() -- 2.11.4.GIT