VOP_GETPAGES (9)

Leading comments

Copyright (c) 1996 Doug Rabson
Copyright 2003, Garrett A. Wollman

All rights reserved.

This program is free software.

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modification, are permitted provided that the following conditions
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1. Redistributions of source code must retain the above copyright
   notice, this list of conditions and the following disclaimer.
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(The comments found at the beginning of the groff file "man9/VOP_GETPAGES.9freebsd".)

NAME

VOP_GETPAGES VOP_PUTPAGES - read or write VM pages from a file

SYNOPSIS

In sys/param.h In sys/vnode.h In vm/vm.h Ft int Fn VOP_GETPAGES struct vnode *vp vm_page_t *ma int count int reqpage vm_ooffset_t offset Ft int Fn VOP_PUTPAGES struct vnode *vp vm_page_t *ma int count int sync int *rtvals vm_ooffset_t offset

DESCRIPTION

The Fn VOP_GETPAGES method is called to read in pages of virtual memory which are backed by ordinary files. If other adjacent pages are backed by adjacent regions of the same file, Fn VOP_GETPAGES is requested to read those pages as well, although it is not required to do so. The Fn VOP_PUTPAGES method does the converse; that is to say, it writes out adjacent dirty pages of virtual memory.

On entry, the vnode lock is held but neither the page queue nor VM object locks are held. Both methods return in the same state on both success and error returns.

The arguments are:

Fa vp

The file to access.

Fa ma

Pointer to the first element of an array of pages representing a contiguous region of the file to be read or written.

Fa count

The number of bytes that should be read into the pages of the array.

Fa sync

VM_PAGER_PUT_SYNC if the write should be synchronous.

Fa rtvals

An array of VM system result codes indicating the status of each page written by Fn VOP_PUTPAGES .

Fa reqpage

The index in the page array of the requested page; i.e., the one page which the implementation of this method must handle.

Fa offset

Offset in the file at which the mapped pages begin.

The status of the Fn VOP_PUTPAGES method is returned on a page-by-page basis in the array Fa rtvals[] . The possible status values are as follows:

VM_PAGER_OK

The page was successfully written. The implementation must call vm_page_undirty9 to mark the page as clean.

VM_PAGER_PEND

The page was scheduled to be written asynchronously. When the write completes, the completion callback should call vm_object_pip_wakeup9 and vm_page_sunbusy9 to clear the busy flag and awaken any other threads waiting for this page, in addition to calling vm_page_undirty9.

VM_PAGER_BAD

The page was entirely beyond the end of the backing file. This condition should not be possible if the vnode's file system is correctly implemented.

VM_PAGER_ERROR

The page could not be written because of an error on the underlying storage medium or protocol.

VM_PAGER_FAIL

Treated identically to VM_PAGER_ERROR

VM_PAGER_AGAIN

The page was not handled by this request.

The Fn VOP_GETPAGES method is expected to release any pages in Fa ma that it does not successfully handle, by calling vm_page_free9. When it succeeds, Fn VOP_GETPAGES must set the valid bits appropriately. Fn VOP_GETPAGES must keep Fa reqpage busy. It must unbusy all other successfully handled pages and put them on appropriate page queue(s). For example, Fn VOP_GETPAGES may either activate a page (if its wanted bit is set) or deactivate it (otherwise), and finally call vm_page_xunbusy9 to arouse any threads currently waiting for the page to be faulted in.

RETURN VALUES

If it successfully reads Fa ma[reqpage] , Fn VOP_GETPAGES returns VM_PAGER_OK otherwise, VM_PAGER_ERROR By convention, the return value of Fn VOP_PUTPAGES is Fa rtvals[0] .

SEE ALSO

vm_object_pip_wakeup9, vm_page_free9, vm_pagge_sunbusy9, vm_page_undirty9, vm_page_xunbusy9, vnode(9)

AUTHORS

This manual page was written by An Doug Rabson and then substantially rewritten by An Garrett Wollman .