[PATCH] generic/486: print correct errno

[Xiao Yang <yangx.jy@cn.fujitsu.com>]

On glibc v2.12 or v2.17, running generic/486 with XFS got wrong
EINVAL instead of ENODATA:
----------------------------------------------------------------
QA output created by 486
No data available
error=22 at line 63
----------------------------------------------------------------

We want to save the correct errno and print it after calling perror().

It seems that only calling perror() didn't change the errno, but calling
perror() and redirecting the output of perror() to a file set errno to
EINVAL.

For example, running the special test.c to reproduce the issue:
------------------------------------------------------------
#include <errno.h>
#include <unistd.h>
#include <stdio.h>

int main(void)
{
        close(-1);
        printf("errno %d before\n", errno);
        perror("");
        printf("errno %d after\n", errno);
}
------------------------------------------------------------
# gcc -o test test.c
# ./test
# ./test 2>log

fdopen() called by perror() in glibc seems to set errno to EINVAL
in some cases(e.g. the access mode of stderr is O_WRONLY). I am not
sure whether this is a perror bug in glibc or not.

Signed-off-by: Xiao Yang <yangx.jy@cn.fujitsu.com>
---
 src/attr_replace_test.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/src/attr_replace_test.c b/src/attr_replace_test.c
index 23adc07..e9a08cc 100644
--- a/src/attr_replace_test.c
+++ b/src/attr_replace_test.c
@@ -10,8 +10,9 @@
 #include <sys/xattr.h>
 #include <sys/stat.h>
 
-#define die() do { perror(""); \
-fprintf(stderr, "error=%d at line %d\n", errno, __LINE__); \
+#define die() do { int real_errno = errno; \
+perror(""); \
+fprintf(stderr, "error=%d at line %d\n", real_errno, __LINE__); \
 exit(1); } while (0)
 
 #define fail(...) do { \
-- 
1.8.3.1