open read file with file descriptor

Question

I use a driver that have many files, each file I have an ID to it, when I open theses files I store the files descriptors in strcut array that contain the ID with the file descriptor, each opened file can be blocking or not.

I want to read the file from another program or from an other function in the program, when I try to read a blocking file with its file descriptor, it don't still blocking until I write on it, it return no data in the buffer, but when I use it in the same function It still blocking.

Where is the problem ?

if (vg_bufObj[indice].protocolType == _NO_BLOC) 
vg_bufObj[indice].dev_fd = open(d_path, O_RDONLY | O_NONBLOCK);
else
vg_bufObj[indice].dev_fd = open(d_path, O_RDONLY);

vg_bufObj is struct and declared extern

in other function I read the file with

read_size = read(vg_bufObj[indice].dev_fd, data, 8);

When the protocolType is specified _BLOC the file is open blocking, but when I read it from the another function it return empty data and the read size return the max value of the variable.

Answer 1

if (vg_bufObj[indice].protocolType == _NO_BLOC) 
vg_bufObj[indice].dev_fd = open(d_path, O_RDONLY | O_NONBLOCK);
else
vg_bufObj[indice].dev_fd = open(d_path, O_RDONLY);

vg_bufObj is struct and declared extern

in other function I read the file with

read_size = read(vg_bufObj[indice].dev_fd, data, 8);

When the protocolType is specified _BLOC the file is open blocking, but when I read it from the another function it return empty data and the read size return the max value of the variable.