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xread/xwrite: clip MAX_IO_SIZE to SSIZE_MAX

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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 <jojo@schmitz-digital.de>
Helped-by: Torsten Bögershausen <tboegi@web.de>
Helped-by: Eric Sunshine <sunshine@sunshineco.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Junio C Hamano 2015-02-11 13:13:10 -08:00
parent 0b6806b9e4
commit a983e6ac58
1 changed files with 15 additions and 1 deletions
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16
wrapper.c
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@ -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()