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#include "sam.h"
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static	Block	*blist;
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static int
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tempdisk(void)
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{
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	char buf[128];
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	int i, fd;
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	snprint(buf, sizeof buf, "/tmp/X%d.%.4ssam", getpid(), getuser());
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	for(i='A'; i<='Z'; i++){
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		buf[5] = i;
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		if(access(buf, AEXIST) == 0)
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			continue;
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		fd = create(buf, ORDWR|ORCLOSE|OCEXEC, 0600);
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		if(fd >= 0)
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			return fd;
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	}
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	return -1;
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}
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Disk*
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diskinit()
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{
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	Disk *d;
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	d = emalloc(sizeof(Disk));
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	d->fd = tempdisk();
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	if(d->fd < 0){
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		fprint(2, "sam: can't create temp file: %r\n");
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		exits("diskinit");
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	}
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	return d;
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}
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static
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uint
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ntosize(uint n, uint *ip)
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{
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	uint size;
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	if(n > Maxblock)
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		panic("internal error: ntosize");
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	size = n;
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	if(size & (Blockincr-1))
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		size += Blockincr - (size & (Blockincr-1));
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	/* last bucket holds blocks of exactly Maxblock */
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	if(ip)
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		*ip = size/Blockincr;
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	return size * sizeof(Rune);
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}
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Block*
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disknewblock(Disk *d, uint n)
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{
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	uint i, j, size;
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	Block *b;
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	size = ntosize(n, &i);
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	b = d->free[i];
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	if(b)
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		d->free[i] = b->next;
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	else{
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		/* allocate in chunks to reduce malloc overhead */
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		if(blist == nil){
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			blist = emalloc(100*sizeof(Block));
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			for(j=0; j<100-1; j++)
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				blist[j].next = &blist[j+1];
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		}
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		b = blist;
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		blist = b->next;
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		b->addr = d->addr;
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		d->addr += size;
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	}
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	b->n = n;
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	return b;
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}
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void
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diskrelease(Disk *d, Block *b)
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{
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	uint i;
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	ntosize(b->n, &i);
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	b->next = d->free[i];
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	d->free[i] = b;
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}
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void
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diskwrite(Disk *d, Block **bp, Rune *r, uint n)
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{
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	int size, nsize;
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	Block *b;
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	b = *bp;
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	size = ntosize(b->n, nil);
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	nsize = ntosize(n, nil);
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	if(size != nsize){
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		diskrelease(d, b);
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		b = disknewblock(d, n);
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		*bp = b;
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	}
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	if(pwrite(d->fd, r, n*sizeof(Rune), b->addr) != n*sizeof(Rune))
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		panic("write error to temp file");
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	b->n = n;
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}
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void
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diskread(Disk *d, Block *b, Rune *r, uint n)
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{
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	if(n > b->n)
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		panic("internal error: diskread");
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	ntosize(b->n, nil);	/* called only for sanity check on Maxblock */
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	if(pread(d->fd, r, n*sizeof(Rune), b->addr) != n*sizeof(Rune))
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		panic("read error from temp file");
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}