NetBSD/sys/kern/kern_physio.c

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/* $NetBSD: kern_physio.c,v 1.20 1994/06/29 06:32:34 cgd Exp $ */
/*-
* Copyright (c) 1994 Christopher G. Demetriou
* Copyright (c) 1982, 1986, 1990, 1993
* The Regents of the University of California. All rights reserved.
* (c) UNIX System Laboratories, Inc.
* All or some portions of this file are derived from material licensed
* to the University of California by American Telephone and Telegraph
* Co. or Unix System Laboratories, Inc. and are reproduced herein with
* the permission of UNIX System Laboratories, Inc.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. All advertising materials mentioning features or use of this software
* must display the following acknowledgement:
* This product includes software developed by the University of
* California, Berkeley and its contributors.
* 4. Neither the name of the University nor the names of its contributors
* may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*
* @(#)kern_physio.c 8.1 (Berkeley) 6/10/93
*/
#include <sys/param.h>
#include <sys/systm.h>
#include <sys/buf.h>
#include <sys/conf.h>
#include <sys/proc.h>
/*
* The routines implemented in this file are described in:
* Leffler, et al.: The Design and Implementation of the 4.3BSD
* UNIX Operating System (Addison Welley, 1989)
* on pages 231-233.
*
* The routines "getphysbuf" and "putphysbuf" steal and return a swap
* buffer. Leffler, et al., says that swap buffers are used to do the
* I/O, so raw I/O requests don't have to be single-threaded.
*/
struct buf *getphysbuf __P((void));
void putphysbuf __P((struct buf *bp));
/*
* Do "physical I/O" on behalf of a user. "Physical I/O" is I/O directly
* from the raw device to user buffers, and bypasses the buffer cache.
*
* Comments in brackets are from Leffler, et al.'s pseudo-code implementation.
*/
int
physio(strategy, bp, dev, flags, minphys, uio)
int (*strategy)();
struct buf *bp;
dev_t dev;
int flags;
u_int (*minphys)();
struct uio *uio;
{
struct iovec *iovp;
struct proc *p = curproc;
int error, done, i, nobuf, s, todo;
error = 0;
flags &= B_READ | B_WRITE;
/*
* [check user read/write access to the data buffer]
*
* Check each iov one by one. Note that we know if we're reading or
* writing, so we ignore the uio's rw parameter. Also note that if
* we're doing a read, that's a *write* to user-space.
*/
for (i = 0; i < uio->uio_iovcnt; i++)
if (!useracc(uio->uio_iov[i].iov_base, uio->uio_iov[i].iov_len,
(flags == B_READ) ? B_WRITE : B_READ))
return (EFAULT);
/* Make sure we have a buffer, creating one if necessary. */
if (nobuf = (bp == NULL))
bp = getphysbuf();
/* [raise the processor priority level to splbio;] */
s = splbio();
/* [while the buffer is marked busy] */
while (bp->b_flags & B_BUSY) {
/* [mark the buffer wanted] */
bp->b_flags |= B_WANTED;
/* [wait until the buffer is available] */
tsleep((caddr_t)bp, PRIBIO+1, "physbuf", 0);
}
/* Mark it busy, so nobody else will use it. */
bp->b_flags |= B_BUSY;
/* [lower the priority level] */
splx(s);
/* [set up the fixed part of the buffer for a transfer] */
bp->b_dev = dev;
bp->b_error = 0;
bp->b_proc = p;
/*
* [while there are data to transfer and no I/O error]
* Note that I/O errors are handled with a 'goto' at the bottom
* of the 'while' loop.
*/
for (i = 0; i < uio->uio_iovcnt; i++) {
iovp = &uio->uio_iov[i];
while (iovp->iov_len > 0) {
/*
* [mark the buffer busy for physical I/O]
* (i.e. set B_PHYS (because it's an I/O to user
* memory, and B_RAW, because B_RAW is to be
* "Set by physio for raw transfers.", in addition
* to the "busy" and read/write flag.)
*/
s = splbio();
bp->b_flags = B_BUSY | B_PHYS | B_RAW | flags;
splx(s);
/* [set up the buffer for a maximum-sized transfer] */
bp->b_blkno = btodb(uio->uio_offset);
bp->b_bcount = iovp->iov_len;
bp->b_data = iovp->iov_base;
/*
* [call minphys to bound the tranfer size]
* and remember the amount of data to transfer,
* for later comparison.
*/
(*minphys)(bp);
todo = bp->b_bcount;
/*
* [lock the part of the user address space involved
* in the transfer]
* Beware vmapbuf(); it clobbers b_data and
* saves it in b_saveaddr. However, vunmapbuf()
* restores it.
*/
p->p_holdcnt++;
vslock(bp->b_data, todo);
vmapbuf(bp, todo);
/* [call strategy to start the transfer] */
(*strategy)(bp);
/*
* Note that the raise/wait/lower/get error
* steps below would be done by biowait(), but
* we want to unlock the address space before
* we lower the priority.
*
* [raise the priority level to splbio]
*/
s = splbio();
/* [wait for the transfer to complete] */
while ((bp->b_flags & B_DONE) == 0)
tsleep((caddr_t) bp, PRIBIO + 1, "physio", 0);
/*
* [unlock the part of the address space previously
* locked]
*/
vunmapbuf(bp, todo);
vsunlock(bp->b_data, todo);
p->p_holdcnt--;
/* remember error value (save a splbio/splx pair) */
if (bp->b_flags & B_ERROR)
error = (bp->b_error ? bp->b_error : EIO);
/* [lower the priority level] */
splx(s);
/*
* [deduct the transfer size from the total number
* of data to transfer]
*/
done = bp->b_bcount - bp->b_resid;
iovp->iov_len -= done;
iovp->iov_base += done;
uio->uio_offset += done;
uio->uio_resid -= done;
/*
* Now, check for an error.
* Also, handle weird end-of-disk semantics.
*/
if (error || done < todo)
goto done;
}
}
done:
/*
* [clean up the state of the buffer]
* Remember if somebody wants it, so we can wake them up below.
* Also, if we had to steal it, give it back.
*/
s = splbio();
bp->b_flags &= ~(B_BUSY | B_PHYS | B_RAW);
if (nobuf)
putphysbuf(bp);
else {
/*
* [if another process is waiting for the raw I/O buffer,
* wake up processes waiting to do physical I/O;
*/
if (bp->b_flags & B_WANTED) {
bp->b_flags &= ~B_WANTED;
wakeup(bp);
}
}
splx(s);
return (error);
}
/*
* Get a swap buffer structure, for use in physical I/O.
* Mostly taken from /sys/vm/swap_pager.c, except that it no longer
* records buffer list-empty conditions, and sleeps at PRIBIO + 1,
* rather than PSWP + 1 (and on a different wchan).
*/
struct buf *
getphysbuf()
{
struct buf *bp;
int s;
s = splbio();
while (bswlist.b_actf == NULL) {
bswlist.b_flags |= B_WANTED;
tsleep((caddr_t)&bswlist, PRIBIO + 1, "getphys", 0);
}
bp = bswlist.b_actf;
bswlist.b_actf = bp->b_actf;
splx(s);
return (bp);
}
/*
* Get rid of a swap buffer structure which has been used in physical I/O.
* Mostly taken from /sys/vm/swap_pager.c, except that it now uses
* wakeup() rather than the VM-internal thread_wakeup(), and that the caller
* must mask disk interrupts, rather than putphysbuf() itself.
*/
void
putphysbuf(bp)
struct buf *bp;
{
bp->b_actf = bswlist.b_actf;
bswlist.b_actf = bp;
if (bp->b_vp)
brelvp(bp);
if (bswlist.b_flags & B_WANTED) {
bswlist.b_flags &= ~B_WANTED;
wakeup(&bswlist);
}
}
/*
* Leffler, et al., says on p. 231:
* "The minphys() routine is called by physio() to adjust the
* size of each I/O transfer before the latter is passed to
* the strategy routine..."
*
* so, just adjust the buffer's count accounting to MAXPHYS here,
* and return the new count;
*/
u_int
minphys(bp)
struct buf *bp;
{
bp->b_bcount = min(MAXPHYS, bp->b_bcount);
return bp->b_bcount;
}
/*
* Do a read on a device for a user process.
*/
rawread(dev, uio)
dev_t dev;
struct uio *uio;
{
return (physio(cdevsw[major(dev)].d_strategy, (struct buf *)NULL,
dev, B_READ, minphys, uio));
}
/*
* Do a write on a device for a user process.
*/
rawwrite(dev, uio)
dev_t dev;
struct uio *uio;
{
return (physio(cdevsw[major(dev)].d_strategy, (struct buf *)NULL,
dev, B_WRITE, minphys, uio));
}