/*---------------------------------------------------------------------------*/
static coffee_page_t
find_contiguous_pages(coffee_page_t amount)
{
coffee_page_t page, start;
struct file_header hdr;
start = INVALID_PAGE;
for(page = *next_free; page < COFFEE_PAGE_COUNT;) {
read_header(&hdr, page);
if(HDR_FREE(hdr)) {
if(start == INVALID_PAGE) {
start = page;
if(start + amount >= COFFEE_PAGE_COUNT) {
/* We can stop immediately if the remaining pages are not enough. */
break;
}
}
/* All remaining pages in this sector are free --
jump to the next sector. */
page = next_file(page, &hdr);
if(start + amount <= page) {
if(start == *next_free) {
*next_free = start + amount;
}
return start;
}
} else {
start = INVALID_PAGE;
page = next_file(page, &hdr);
}
}
return INVALID_PAGE;
}
/*---------------------------------------------------------------------------*/
static coffee_page_t
next_file(coffee_page_t page, struct file_header *hdr)
{
if(HDR_FREE(*hdr)) {
return (page + COFFEE_PAGES_PER_SECTOR) & ~(COFFEE_PAGES_PER_SECTOR - 1);
} else if(HDR_ISOLATED(*hdr)) {
return page + 1;
}
return page + hdr->max_pages;
}
/*---------------------------------------------------------------------------*/
static coffee_page_t
next_file(coffee_page_t page, struct file_header *hdr)
{
/*
* The quick-skip algorithm for finding file extents is the most
* essential part of Coffee. The file allocation rules enables this
* algorithm to quickly jump over free areas and allocated extents
* after reading single headers and determining their status.
*
* The worst-case performance occurs when we encounter multiple long
* sequences of isolated pages, but such sequences are uncommon and
* always shorter than a sector.
*/
if(HDR_FREE(*hdr)) {
return (page + COFFEE_PAGES_PER_SECTOR) & ~(COFFEE_PAGES_PER_SECTOR - 1);
} else if(HDR_ISOLATED(*hdr)) {
return page + 1;
}
return page + hdr->max_pages;
}
