[sheepdog] [PATCH v2] lib: fix compiler error in logger.c

[Robin Dong]

From: Robin Dong <sanbai at taobao.com>

When build sheepdog in centos6, it will report:

    logger.c: In function ‘gdb_cmd’:
    logger.c:746: error: ‘ARG_MAX’ undeclared (first use in this function)
    logger.c:746: error: (Each undeclared identifier is reported only once
    logger.c:746: error: for each function it appears in.)
    logger.c:746: warning: unused variable ‘cmd_str’
    logger.c: In function ‘sd_backtrace’:
    logger.c:797: error: ‘ARG_MAX’ undeclared (first use in this function)
    logger.c:797: warning: unused variable ‘cmd’

the reason has been explained here: http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=518858
and the standard revolution is using 'sysconf()'.

Signed-off-by: Robin Dong <sanbai at taobao.com>
---
 lib/logger.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/lib/logger.c b/lib/logger.c
index 8be2bfd..267b87d 100644
--- a/lib/logger.c
+++ b/lib/logger.c
@@ -741,6 +741,8 @@ static bool check_gdb(void)
 	return system("which gdb > /dev/null") == 0;
 }
 
+#define ARG_MAX (sysconf(_SC_ARG_MAX))
+
 static int gdb_cmd(const char *cmd)
 {
 	char time_str[256], cmd_str[ARG_MAX];
-- 
1.7.12.4