c - Pinned memory with offset in OpenCL -

so i'm reading data in file using mmap() follows :

unsigned char* mapped; mapped = mmap(0,size,prot_read,map_private,input,0); 

then created host buffer , device buffer pinned memory :

cl_mem pinned_buffer_input = clcreatebuffer(context, cl_mem_read_only | cl_mem_alloc_host_ptr, size, mapped, null); cl_mem buffer_input = clcreatebuffer(context, cl_mem_read_only, input_size, null, null); 

within for loop :

• mapping buffer :

  void *pinnedmemory = clenqueuemapbuffer(cmd_queue, pinned_buffer_input, cl_true, cl_map_write, header[3]+b*input_size, input_size_cur, 0, null, &ev, null); 

• enqueuing buffer :

  clenqueuewritebuffer(cmd_queue, buffer_input, cl_false, 0, input_size_cur, pinnedmemory, 0, null, &ev); 

• unmapping object :

  clenqueueunmapmemobject(cmd_queue, pinned_buffer_input, pinnedmemory, 0, null, &ev); 

here mapped contains whole file , of size size. want have buffers of size input_size (or input_size_cur, same thing simplify) send data blocks. offset header[3]+b*input_size b incremented in loop copies wrong data.

edit : if don't initialize pinned_buffer_input mapped can pointer host buffer clenqueuemapbuffer() , copy data of mapped place :

memcpy(pinnedmemory, mapped+header[3]+b*input_size, input_size_cur); 

by doing works want avoid memcpy in for loop , creates huge delays in program. solve problem wanted use offset parameter of clenqueuemapbuffer() screws up.

edit 2 : cl_mem_copy_host_ptr instead of cl_mem_alloc_host_ptr result correct takes ages create pinned_buffer_input.

i haven't got clear picture tell why not working guesses are:

• are waiting unmap/write complete?
• how checking data writen properly? if reading back, how reading back? maybe problem there well.