boot/common/bcache.c

/*
 * mjs copyright
 */

/*
 * Simple LRU block cache
 */

#include <stand.h>
#include <string.h>
#include <bitstring.h>

#include "bootstrap.h"

/* #define BCACHE_DEBUG */

#ifdef BCACHE_DEBUG
#define BCACHE_TIMEOUT	10
# define DEBUG(fmt, args...)	printf("%s: " fmt "\n" , __FUNCTION__ , ## args)
#else
#define BCACHE_TIMEOUT	2
# define DEBUG(fmt, args...)
#endif


struct bcachectl
{
    daddr_t	bc_blkno;
    time_t	bc_stamp;
};

static struct bcachectl	*bcache_ctl;
static caddr_t		bcache_data;
static bitstr_t		*bcache_miss;
static int		bcache_nblks;
static int		bcache_blksize;
static int		bcache_hits, bcache_misses, bcache_ops, bcache_bypasses;

static void	bcache_insert(caddr_t buf, daddr_t blkno);
static int	bcache_lookup(caddr_t buf, daddr_t blkno);

/*
 * Initialise the cache for (nblks) of (bsize).
 */
int
bcache_init(int nblks, size_t bsize)
{
    int		i;

    /* discard any old contents */
    if (bcache_data != NULL) {
	free(bcache_data);
	bcache_data = NULL;
	free(bcache_ctl);
    }

    /* Allocate control structures */
    bcache_nblks = nblks;
    bcache_blksize = bsize;
    bcache_data = malloc(bcache_nblks * bcache_blksize);
    bcache_ctl = (struct bcachectl *)malloc(bcache_nblks * sizeof(struct bcachectl));
    bcache_miss = bit_alloc((bcache_nblks + 1) / 2);
    if ((bcache_data == NULL) || (bcache_ctl == NULL) || (bcache_miss == NULL)) {
	if (bcache_miss)
	    free(bcache_miss);
	if (bcache_ctl)
	    free(bcache_ctl);
	if (bcache_data)
	    free(bcache_data);
	bcache_data = NULL;
	return(ENOMEM);
    }

    /* Invalidate the cache */
    for (i = 0; i < bcache_nblks; i++)
	bcache_ctl[i].bc_stamp = 0;

    return(0);
}

/*
 * Handle a transfer request; fill in parts of the request that can
 * be satisfied by the cache, use the supplied strategy routine to do
 * device I/O and then use the I/O results to populate the cache.
 *
 * Requests larger than 1/2 the cache size will be bypassed and go
 * directly to the disk.  XXX tune this.
 */
int
bcache_strategy(void *devdata, int rw, daddr_t blk, size_t size, void *buf, size_t *rsize)
{
    struct bcache_devdata	*dd = (struct bcache_devdata *)devdata;
    int				nblk, p_size;
    daddr_t			p_blk;
    caddr_t			p_buf;
    int				i, j, result;

    bcache_ops++;

    /* bypass large requests, or when the cache is inactive */
    if ((bcache_data == NULL) || ((size * 2 / bcache_blksize) > bcache_nblks)) {
	DEBUG("bypass %d from %d", size / bcache_blksize, blk);
	bcache_bypasses++;
	return(dd->dv_strategy(dd->dv_devdata, rw, blk, size, buf, rsize));
    }

    nblk = size / bcache_blksize;
    result = 0;

    /* Satisfy any cache hits up front */
    for (i = 0; i < nblk; i++) {
	if (bcache_lookup(buf + (bcache_blksize * i), blk + i)) {
	    bit_set(bcache_miss, i);	/* cache miss */
	    bcache_misses++;
	} else {
	    bit_clear(bcache_miss, i);	/* cache hit */
	    bcache_hits++;
	}
    }

    /* Go back and fill in any misses  XXX optimise */
    p_blk = -1;
    p_buf = NULL;
    p_size = 0;
    for (i = 0; i < nblk; i++) {
	if (bit_test(bcache_miss, i)) {
	    /* miss, add to pending transfer */
	    if (p_blk == -1) {
		p_blk = blk + i;
		p_buf = buf + (bcache_blksize * i);
		p_size = 1;
	    } else {
		p_size++;
	    }
	} else if (p_blk != -1) {
	    /* hit, complete pending transfer */
	    result = dd->dv_strategy(dd->dv_devdata, rw, p_blk, p_size * bcache_blksize, p_buf, NULL);
	    if (result != 0)
		goto done;
	    for (j = 0; j < p_size; j++)
		bcache_insert(p_buf + (j * bcache_blksize), p_blk + j);
	    p_blk = -1;
	}
    }
    if (p_blk != -1) {
	/* pending transfer left */
	result = dd->dv_strategy(dd->dv_devdata, rw, p_blk, p_size * bcache_blksize, p_buf, NULL);
	if (result != 0)
	    goto done;
	for (j = 0; j < p_size; j++)
	    bcache_insert(p_buf + (j * bcache_blksize), p_blk + j);
    }

 done:
    if ((result == 0) && (rsize != NULL))
	*rsize = size;
    return(result);
}


/*
 * Insert a block into the cache.  Retire the oldest block to do so, if required.
 */
static void
bcache_insert(caddr_t buf, daddr_t blkno)
{
    time_t	now;
    int		i, cand;

    time(&now);

    /* find the oldest block */
    for (cand = 0, i = 1; i < bcache_nblks; i++) {
	if (bcache_ctl[i].bc_blkno == blkno) {
	    /* reuse old entry */
	    cand = i;
	    break;
	}
	if (bcache_ctl[i].bc_stamp < now)
	    cand = i;
    }

    DEBUG("insert blk %d -> %d @ %d", blkno, cand, now);
    bcopy(buf, bcache_data + (bcache_blksize * cand), bcache_blksize);
    bcache_ctl[cand].bc_blkno = blkno;
    bcache_ctl[cand].bc_stamp = now;
}

/*
 * Look for a block in the cache.  Blocks more than BCACHE_TIMEOUT seconds old
 *  may be stale (removable media) and thus are discarded.  Copy the block out
 * if successful and return zero, or return nonzero on failure.
 */
static int
bcache_lookup(caddr_t buf, daddr_t blkno)
{
    time_t	now;
    int		i;

    time(&now);

    for (i = 0; i < bcache_nblks; i++)
	/* cache hit? */
	if ((bcache_ctl[i].bc_blkno == blkno) && ((bcache_ctl[i].bc_stamp + BCACHE_TIMEOUT) >= now)) {
	    bcopy(bcache_data + (bcache_blksize * i), buf, bcache_blksize);
	    DEBUG("hit blk %d <- %d (now %d then %d)", blkno, i, now, bcache_ctl[i].bc_stamp);
	    return(0);
	}
    return(ENOENT);
}

COMMAND_SET(bcachestat, "bcachestat", "get disk block cache stats", command_bcache);

static int
command_bcache(int argc, char *argv[])
{
    int		i;

    for (i = 0; i < bcache_nblks; i++) {
	printf("  %02x: %08x %04x", i, bcache_ctl[i].bc_blkno, bcache_ctl[i].bc_stamp & 0xffff);
	if (((i + 1) % 4) == 0)
	    printf("\n");
    }
    printf("\n%d ops  %d bypasses  %d hits  %d misses\n", bcache_ops, bcache_bypasses, bcache_hits, bcache_misses);
    return(CMD_OK);
}