How to handle partial reads with read() function in C - c

Question

I have to implement standard unix command "tail" without fopen, fclose, fread, fseek, printf. I am ready with everything else except handle of partial reads and writes.
And here is my print with handle of partial read and write of last 10 lines. It's happening after lseek to the right position for fd!
I test it several times with different files and it works like real tail, but i cant handle partial reads and writes like i said.
'''code'''
do
{
memset(buff, 0, SIZE);
read_value = read(fd, buff, SIZE);
ssize_t bytes_read_total = read_value;
int count=2;
char buff_copy[SIZE];
while (bytes_read_total < SIZE)
{
read_value = read(fd, buff + bytes_read_total, SIZE - bytes_read_total);
if(count%2==0)
strcpy(buff_copy, buff);
if (read_value == -1)
{
char *err;
err = (char *)malloc(sizeof(char)*(50+strlen(file)));
strcpy(err, "tail: error reading '");
strcat(err, file);
strcat(err, "'");
perror(err);
free(err);
return 2;
}
if(read_value==0)
{
strcpy(buff, buff_copy);
read_value = strlen(buff_copy);
break;
}
bytes_read_total+= read_value;
}
ssize_t bytes_written;
ssize_t bytes_written_total = 0;
while (read_value != bytes_written_total)
{
bytes_written = write(STDOUT_FILENO, buff+bytes_written_total, read_value - bytes_written_total);
if (bytes_written == -1)
{
perror("tail: error writing 'standard output'");
return 3;
}
bytes_written_total += bytes_written;
}
}while(read_value);
'''code'''