Description of problem:
Reading over than the file size on dispersed volume

Version-Release number of selected component (if applicable):
3.12.1-2

How reproducible:

------------------------------------------------------
Volume Name: TEST_VOL
Type: Disperse
Volume ID: be52b68d-ae83-46e3-9527-0e536b867bcc
Status: Started
Snapshot Count: 0
Number of Bricks: 1 x (6 + 3) = 9
Transport-type: tcp
Bricks:
Brick1: server1:/data/brick1
Brick2: server2:/data/brick1
Brick3: server3:/data/brick1
Brick4: server1:/data/brick2
Brick5: server2:/data/brick2
Brick6: server3:/data/brick2
Brick7: server1:/data/brick3
Brick8: server2:/data/brick3
Brick9: server3:/data/brick3
Options Reconfigured:
network.ping-timeout: 10
performance.write-behind: on
features.quota-deem-statfs: on
features.inode-quota: on
features.quota: on
transport.address-family: inet
nfs.disable: on
------------------------------------------------------

Steps to Reproduce:
1. generating the temporary files like below command.
fallocate -l 130394  test1 
fallocate -l 667417658  test2
fallocate -l 2493251482 test3 

2. reading the files to EOF like below sources
--------------------------------------------------------------
 glfs_fd_t* fd = glfs_open (gluster_fs, "/test1", O_RDWR);

    size_t retr = 0;
    off_t offset = 0;
    unsigned char buf[128*1024] = {0,};

    while ((retr = glfs_pread(fd, buf, sizeof(buf), offset, 0)) > 0) {
        printf("retr : %ld, offset : %ld(%d) \n", retr, offset, errno);
        offset += retr;
    }

    printf("offset : %d\n", offset);
-----------------------------------------------------------------------------------------------------------------

Actual results:
print debug 

retr : 130394, offset : 42(0)
retr : 1024, offset : 130436(0)
retr : 636, offset : 131460(0)
offset : 132096(0)

Expected results:
The reading size (total offset) has to be the same with original file size
offset : 130394

Additional info:

Why the glfs_pread(or glfs_read) function reads until over than the file size ?

This is fine on dispersed (4+2) and (8+1) volume but it is occurred on (6+3) or (6+4) or (7+2) disperse volume.
I want to know exact cause.
Thank you.