[syslinux] malloc() in the core

[H. Peter Anvin]

Hi guys,

I just looked over liu's code as of today, and it looks pretty good;
obviously you have gotten a huge amount of work done already!

However, in the short term, we will most likely not have memory
management -- malloc/free -- available in the core (making that possible
is part of KlausM's project, but I want to decouple those.)

The code currently uses malloc() in disklab.c, which is used from
cache.c.  The solution there is pretty simple: add a pointer to get
getoneblk() prototype for a target buffer, then use a chunk of .bss
memory for the cache.

As previously discussed, we really want the cache system to handle
multiple block sizes (first of all, because hard disks are going to be
changing from 512 to 4K sectors over the next several years, and second
because filesystems like ext2 have metadata which is more logically
cached on the filesystem block level):

static struct cache_struct cache_head, cache[MAX_CACHE_ENTRIES];
static uint8_t cache_data[65536];
static int cache_block_size;
static int cache_entries;

void cache_init(int block_size)
{
        struct cache_struct *prev, *cur;
	uint8_t *data = cache_data;
        int i;

	cache_block_size = block_size;
	cache_entries = sizeof cache_data / block_size;
	if (cache_entries > MAX_CACHE_ENTRIES)
		cache_entries = MAX_CACHE_ENTRIES;

        cache_head.prev = &cache[cache_entries-1];
	cache_head.prev->next = &cache_head;
	prev = &cache_head;

        for (i = 0; i < cache_entries; i++) {
		cur = cache[i];
                cur->block = 0;
                cur->prev  = prev;
                prev->next = cur;
                cur->data  = data;
		data += block_size;
                prev = cur++;
	}
}

There is also one use of malloc() in search_dos_dir, but it looks like
it can simply be replaced by an automatic (stack) variable, either a
simple array or using alloca().

(It also doesn't look like it gets freed in the current code, which is
another good hint that it should be replaced by an automatic allocation.)

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.