Cannot access EFS file programmatically with 32bits executable (on a 64bits OS) - c

Question

I've got a problem accessing files programmatically on an Amazon EFS filesystem : the same C program will work with a 64 bits executable, but not with a 32bits executable.
Mount point is /EFS, the program below will list both EFS directory (/EFS/data) and local directory (/home/centos) :
Here is the test program :
#include <stdio.h>
#include <dirent.h>
int main(void) {
struct dirent *d;
char efs_dir[] = "/EFS/data";
char local_dir[] = "/home/centos";
printf("EFS dir : %s\n",efs_dir);
DIR *dirEFS = opendir(efs_dir);
if (dirEFS == NULL) {
printf("Could not open current directory");
return 1;
}
while ((d = readdir(dirEFS)) != NULL)
printf("%s\n", d->d_name);
closedir(dirEFS);
printf("\nlocal filesystem dir : %s\n",local_dir);
DIR *dirLOCAL = opendir(local_dir);
if (dirLOCAL == NULL) {
printf("Could not open current directory");
return 1;
}
while ((d = readdir(dirLOCAL)) != NULL)
printf("%s\n", d->d_name);
closedir(dirLOCAL);
return 0;
}
Unix view :
[centos#ec2-instance ~]$ df -h
Filesystem Size Used Avail Use% Mounted on
/dev/nvme0n1p1 20G 3.4G 16G 19% /
tmpfs 3.7G 0 3.7G 0% /dev/shm
/dev/nvme1n1p1 94G 6.1G 83G 7% /opt/data
fs-XXXXXXXX.eu-west-3.amazonaws.com:/
8.0E 5.3G 8.0E 1% /EFS
[centos#ec2-instance ~]$]$ ls -l /EFS/data
-rw-r--r-- 1 centos centos 2796 Sep 15 12:18 efs_file1.txt
-rw-r--r-- 1 centos centos 2812 Sep 15 12:18 efs_file2.txt
-rw-r--r-- 1 centos centos 3625 Sep 15 12:18 efs_file3.txt
-rw-r--r-- 1 centos centos 2768 Sep 15 12:18 efs_file4.txt
[centos#ec2-instance ~]$]$ ls -l /home/centos
-rw-rw-r-- 1 centos centos 2796 Sep 15 14:15 local_file1.txt
-rw-rw-r-- 1 centos centos 2812 Sep 15 14:15 local_file2.txt
-rw-rw-r-- 1 centos centos 3625 Sep 15 14:15 local_file3.txt
-rw-rw-r-- 1 centos centos 2768 Sep 15 14:15 local_file4.txt
-rw-r--r-- 1 centos centos 792 Sep 15 14:21 test_dir.c
-rwxrwxr-x 1 centos centos 7392 Sep 15 14:22 test_dir
When I compile test_dir.c in 32 bits compatibility mode, no results for the EFS directory :
[centos#ec2-instance ~]$ gcc test_dir.c -o test_dir -m32
[centos#ec2-instance ~]$ ./test_dir
EFS dir : /EFS/data
local filesystem dir : /home/centos
test_dir
.
..
local_file1.txt
local_file2.txt
local_file3.txt
local_file4.txt
test_dir.c
But for 64 bits executable it is fine :
[centos#ec2-instance ~]$ gcc test_dir.c -o test_dir
[centos#ec2-instance ~]$ ./test_dir
EFS dir : /EFS/data
.
..
efs_file1.txt
efs_file2.txt
efs_file3.txt
efs_file4.txt
local filesystem dir : /home/centos
test_dir
.
..
local_file1.txt
local_file2.txt
local_file3.txt
local_file4.txt
test_dir.c
Anyone has an idea of what is happening here ?
Thanks.
edit (solution) : compress the 64 bits inodes number to 32 bits with the kernel option nfs.enable_ino64=0
[root#eai ~]# cat /etc/modprobe.d/nfs.conf
options nfs enable_ino64=0
[root#eai ~]# reboot
and it's done ! Thanks DNT.

Answer 1

Function readdir returns an inode. In your 32bit build it expects to find 32bit inodes. But with a file system with 64bit inodes it will fail if the particular inode number cannot be expressed in 32bits.
To see the inode numbers you may want to use ls -li /EFS/data/efs_file1.txt. The leftmost number is the inode number and if it exceeds 4294967295 then it is 64bit and 32bit readdir cannot handle it.