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/*
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 * Buffered I/O on block devices.
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 * Write buffering ignores offset.
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 */
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#include <u.h>
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#include <libc.h>
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#include <disk.h>
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#include "dat.h"
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#include "fns.h"
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Buf*
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bopen(long (*fn)(Buf*, void*, long, ulong), int omode, int bs, int nblock)
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{
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	Buf *b;
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	assert(omode == OREAD || OWRITE);
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	assert(bs > 0 && nblock > 0);
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	assert(fn != nil);
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	b = emalloc(sizeof(*b));
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	b->data = emalloc(bs*nblock);
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	b->ndata = 0;
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	b->nblock = nblock;
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	b->bs = bs;
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	b->omode = omode;
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	b->fn = fn;		/* function to read or write bs-byte blocks */
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	return b;
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}
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long
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bread(Buf *b, void *v, long n, vlong off)
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{
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	long m;
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	vlong noff;
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	assert(b->omode == OREAD);
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	/* Refill buffer */
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	if(b->off > off || off >= b->off+b->ndata) {
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		noff = off - off % b->bs;
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		if(vflag > 1)
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			fprint(2, "try refill at %lld...", noff);
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		if((m = b->fn(b, b->data, b->nblock, noff/b->bs)) <= 0) {
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			if (vflag)
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				fprint(2, "read failed: %r\n");
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			return m;
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		}
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		b->ndata = b->bs * m;
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		b->off = noff;
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		if(vflag > 1)
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			fprint(2, "got %ld\n", b->ndata);
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	}
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//	fprint(2, "read %ld at %ld\n", n, off);
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	/* Satisfy request from buffer */
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	off -= b->off;
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	if(n > b->ndata - off)
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		n = b->ndata - off;
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	memmove(v, b->data+off, n);
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	return n;
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}
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long
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bwrite(Buf *b, void *v, long n)
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{
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	long on, m, mdata;
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	uchar *p;
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	p = v;
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	on = n;
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	/* Fill buffer */
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	mdata = b->bs*b->nblock;
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	m = mdata - b->ndata;
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	if(m > n)
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		m = n;
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	memmove(b->data+b->ndata, p, m);
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	p += m;
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	n -= m;
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	b->ndata += m;
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	/* Flush buffer */
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	if(b->ndata == mdata) {
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		if(b->fn(b, b->data, b->nblock, 0) < 0) {
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			if(vflag)
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				fprint(2, "write fails: %r\n");
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			return -1;
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		}
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		b->ndata = 0;
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	}
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	/* For now, don't worry about big writes; 9P only does 8k */
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	assert(n < mdata);
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	/* Add remainder to buffer */
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	if(n) {
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		memmove(b->data, p, n);
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		b->ndata = n;
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	}
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	return on;
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}
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void
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bterm(Buf *b)
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{
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	/* DVD & BD prefer full ecc blocks (tracks), but can cope with less */
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	if(b->omode == OWRITE && b->ndata)
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		b->fn(b, b->data, (b->ndata + b->bs - 1)/b->bs, 0);
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	free(b->data);
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	free(b);
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}