to understand the code- how the heap is written in process migration in solaris
- by akshay
hi guys i need help understanding what this piece of code actually does as it is a part of my project i am stuck here. the code is from libckpt on solaris.
/**********************************
* function: write_heap
* args: map_fd -- file descriptor for map file
* data_fd -- file descriptor for data file
* returns: no. of chunks written on success, -1 on failure
* side effects: writes all included segments of the heap to ckpt files
* misc.: If we are forking and copyonwrite is set, we will write the
heap from bottom to top, moving the brk pointer up each time
so that we don't get a page copied if the
* called from: take_ckpt()
***********************************/
static int write_heap(int map_fd, int data_fd)
{
Dlist curptr, endptr;
int no_chunks=0, pn;
long size;
caddr_t stop, addr;
if(ckptflags.incremental){ /-- incremental checkpointing on? --/
endptr = ckptglobals.inc_list-main-flink;
/*-- for each included chunk of the heap --*/
for(curptr = ckptglobals.inc_list->main->blink->blink;
curptr != endptr; curptr = curptr->blink){
/*-- write out the last page in the included chunk --*/
stop = curptr->addr;
pn = ((long)curptr->stop - (long)sys.DATASTART) / PAGESIZE;
if(isdirty(pn)){
addr = (caddr_t)max((long)curptr->addr,
(long)((pn * PAGESIZE) + sys.DATASTART));
size = (long)curptr->stop - (long)addr;
debug(stderr, "DEBUG: Writing heap from 0x%x to 0x%x, pn = %d\n",
addr, addr+size, pn);
if(write_chunk(addr, size, map_fd, data_fd) == -1){
return -1;
}
if((int)addr > (int)(&end) && ckptflags.enhanced_fork){
brk(addr);
}
no_chunks++;
}
/*-- write out all the whole pages in the middle of the chunk --*/
for(pn--; pn * PAGESIZE + sys.DATASTART >= stop; pn--){
if(isdirty(pn)){
addr = (caddr_t)((pn * PAGESIZE) + sys.DATASTART);
debug(stderr, "DEBUG: Writing heap from 0x%x to 0x%x, pn = %d\n",
addr, addr+PAGESIZE, pn);
if(write_chunk(addr, PAGESIZE, map_fd, data_fd) == -1){
return -1;
}
if((int)addr > (int)(&end) && ckptflags.enhanced_fork){
brk(addr);
}
no_chunks++;
}
}
/*-- write out the first page in the included chunk --*/
addr = curptr->addr;
size = ((pn+1) * PAGESIZE + sys.DATASTART) - addr;
if(size > 0 && (isdirty(pn))){
debug(stderr, "DEBUG: Writing heap from 0x%x to 0x%x\n", addr, addr+size);
if(write_chunk(addr, size, map_fd, data_fd) == -1){
return -1;
}
if((int)addr > (int)(&end) && ckptflags.enhanced_fork){
brk(addr);
}
no_chunks++;
}
}
}
else{ /-- incremental checkpointing off! --/
endptr = ckptglobals.inc_list-main-blink;
/*-- for each included chunk of the heap --*/
for(curptr = ckptglobals.inc_list->main->flink->flink;
curptr != endptr; curptr = curptr->flink){
debug(stderr, "DEBUG: saving memory from 0x%x to 0x%x\n",
curptr->addr, curptr->addr+curptr->size);
if(write_chunk(curptr->addr, curptr->size, map_fd, data_fd) == -1){
return -1;
}
if((int)addr > (int)(&end) && ckptflags.enhanced_fork){
brk(addr);
}
no_chunks++;
}
}
return no_chunks;
}
