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Close an interrupt race between vm_page_lookup() and (typically) a
vm_page_sleep_busy() check by using the correct spl protection.
An interrupt can occur inbetween the two operations and unbusy/free
the page in question, causing the busy check to fail and for the code
to fall through and then operate on a page that may have been freed
and possibly even reused.   Also note that vm_page_grab() had the same
issue between the lookup, busy check, and vm_page_busy() call.

Close an interrupt race when scanning a VM object's memq.  Interrupts
can free pages, removing them from memq, which interferes with memq scans
and can cause a page unassociated with the object to be processed as if it
were associated with the object.

Calls to vm_page_hold() and vm_page_unhold() require spl protection.

Rename the passed socket descriptor argument in sendfile() to make the
code more readable.

Fix several serious bugs in procfs_rwmem().  In particular, force it to
block if a page is busy and then retry.

Get rid of vm_pager_map_pag() and vm_pager_unmap_page(), make the functions
that used to use these routines use SFBUF's instead.

Get rid of the (userland?) 4MB page mapping feature in pmap_object_init_pt()
for now.  The code appears to not track the page directory properly and
could result in a non-zero page being freed as PG_ZERO.

This commit also includes updated code comments and some additional
non-operational code cleanups.

/*
 * Copyright (c) 2004 Matthew Dillon <dillon@backplane.com>
 * All rights reserved.
 *
 * 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.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR 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 AUTHOR 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.
 *
 * $DragonFly: src/sys/sys/xio.h,v 1.3 2004/05/13 17:40:17 dillon Exp $
 */

/*
 * The XIO structure is intended to replace UIO for messaged I/O operations
 * within the kernel.  The originator of the transaction must supply an XIO
 * structure containing a list of appropriate held vm_page's representing
 * the buffer.  The target of the transaction will generally map the
 * pages using the SF_BUF facility, complete the operation, and reply the
 * message.
 */
#ifndef _SYS_XIO_H_
#define	_SYS_XIO_H_

#if defined(_KERNEL) || defined(_KERNEL_STRUCTURES)

#ifndef _SYS_MSGPORT_H_
#include <sys/msgport.h>
#endif

#define XIO_INTERNAL_PAGES	btoc(MAXPHYS)
#define XIO_INTERNAL_SIZE	(XIO_INTERNAL_PAGES * PAGE_SIZE)

struct vm_page;

struct xio {
	struct vm_page **xio_pages;
	int	xio_npages;	/* number of pages in xio_pages[] array */
	int	xio_offset;	/* byte offset (may exceed a page) */
	int	xio_bytes;	/* number of bytes to transfer */
	int	xio_flags;
	int	xio_error;
	struct vm_page *xio_internal_pages[XIO_INTERNAL_PAGES];
};

typedef struct xio *xio_t;

#define XIOF_READ	0x0001
#define XIOF_WRITE	0x0002
#define XIOF_LINMAP	0x0004

#endif

#if defined(_KERNEL)

int xio_init_ubuf(xio_t xio, void *ubase, size_t ubytes, int vmprot);
int xio_init_kbuf(xio_t xio, void *kbase, size_t kbytes);
void xio_release(xio_t xio);
int xio_uio_copy(xio_t xio, struct uio *uio, int *sizep);
int xio_copy_xtou(xio_t xio, void *uptr, int bytes);
int xio_copy_xtok(xio_t xio, void *kptr, int bytes);

#endif /* _KERNEL */

#endif /* !_SYS_XIO_H_ */