cache.c

/*
 * CACHE.C
 *
 *	Block cache for dump
 */

#include <sys/param.h>
#include <sys/stat.h>
#include <sys/mman.h>

#ifdef sunos
#include <sys/vnode.h>

#include <ufs/fs.h>
#include <ufs/fsdir.h>
#include <ufs/inode.h>
#else
#include <ufs/ufs/dir.h>
#include <ufs/ufs/dinode.h>
#include <ufs/ffs/fs.h>
#endif

#include <protocols/dumprestore.h>

#include <ctype.h>
#include <stdio.h>
#ifdef __STDC__
#include <errno.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#endif
#include "dump.h"

typedef struct Block {
	struct Block	*b_HNext;	/* must be first field */
	off_t		b_Offset;
	char		*b_Data;
} Block;

#define HFACTOR		4
#define BLKFACTOR	4

static char  *DataBase;
static Block **BlockHash;
static int   BlockSize;
static int   HSize;
static int   NBlocks;

static void
cinit(void)
{
	int i;
	int hi;
	Block *base;

	if ((BlockSize = sblock->fs_bsize * BLKFACTOR) > MAXBSIZE)
		BlockSize = MAXBSIZE;
	NBlocks = cachesize / BlockSize;
	HSize = NBlocks / HFACTOR;

	msg("Cache %d MB, blocksize = %d\n", 
	    NBlocks * BlockSize / (1024 * 1024), BlockSize);

	base = calloc(sizeof(Block), NBlocks);
	BlockHash = calloc(sizeof(Block *), HSize);
	DataBase = mmap(NULL, NBlocks * BlockSize, 
			PROT_READ|PROT_WRITE, MAP_ANON, -1, 0);
	for (i = 0; i < NBlocks; ++i) {
		base[i].b_Data = DataBase + i * BlockSize;
		base[i].b_Offset = (off_t)-1;
		hi = i / HFACTOR;
		base[i].b_HNext = BlockHash[hi];
		BlockHash[hi] = &base[i];
	}
}

ssize_t
cread(int fd, void *buf, size_t nbytes, off_t offset)
{
	Block *blk;
	Block **pblk;
	Block **ppblk;
	int hi;
	int n;
	off_t mask;

	/*
	 * If the cache is disabled, or we do not yet know the filesystem
	 * block size, then revert to pread.  Otherwise initialize the
	 * cache as necessary and continue.
	 */
	if (cachesize <= 0 || sblock->fs_bsize == 0)
		return(pread(fd, buf, nbytes, offset));
	if (DataBase == NULL)
		cinit();

	/*
	 * If the request crosses a cache block boundary, or the
	 * request is larger or equal to the cache block size,
	 * revert to pread().  Full-block-reads are typically
	 * one-time calls and caching would be detrimental.
	 */
	mask = ~(off_t)(BlockSize - 1);
	if (nbytes >= BlockSize ||
	    ((offset ^ (offset + nbytes - 1)) & mask) != 0) {
		return(pread(fd, buf, nbytes, offset));
	}

	/*
	 * Obtain and access the cache block.  Cache a successful
	 * result.  If an error occurs, revert to pread() (this might
	 * occur near the end of the media).
	 */
	hi = (offset / BlockSize) % HSize;
	pblk = &BlockHash[hi];
	ppblk = NULL;
	while ((blk = *pblk) != NULL) {
		if (((blk->b_Offset ^ offset) & mask) == 0)
			break;
		ppblk = pblk;
		pblk = &blk->b_HNext;
	}
	if (blk == NULL) {
		blk = *ppblk;
		pblk = ppblk;
		blk->b_Offset = offset & mask;
		n = pread(fd, blk->b_Data, BlockSize, blk->b_Offset);
		if (n != BlockSize) {
			blk->b_Offset = (off_t)-1;
			blk = NULL;
		}
	}
	if (blk) {
		bcopy(blk->b_Data + (offset - blk->b_Offset), buf, nbytes);
		*pblk = blk->b_HNext;
		blk->b_HNext = BlockHash[hi];
		BlockHash[hi] = blk;
		return(nbytes);
	} else {
		return(pread(fd, buf, nbytes, offset));
	}
}