VOP_GETPAGES(9)

NAME
VOP_GETPAGES, VOP_PUTPAGES - read or write VM pages from a file

SYNOPSIS
#include <sys/param.h>
#include <sys/vnode.h>
#include <vm/vm.h>
int
VOP_GETPAGES(struct vnode *vp, vm_page_t *ma, int count, int reqpage, vm_ooffset_t offset);
int
VOP_PUTPAGES(struct vnode *vp, vm_page_t *ma, int count, int sync, int *rtvals, vm_ooffset_t offset);

DESCRIPTION
The 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, VOP_GETPAGES() is requested to read those pages as well, although it is not required to do so. The 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:

vp  The file to access.

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

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

sync
    VM_PAGER_PUT_SYNC if the write should be synchronous.

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

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

offset
    Offset in the file at which the mapped pages begin.

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

VM_PAGER_OK
    The page was successfully written. The implementation must call vm_page_undirty(9) 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_wakeup(9) and vm_page_io_finish(9) to clear the busy flag and awaken any other threads waiting for this page, in addition to calling vm_page_undirty(9).

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 VOP_GETPAGES() method is expected to release any pages in ma that it does not successfully handle, by calling vm_page_free(9). When it succeeds, VOP_GETPAGES() must set the valid bits appropriately. VOP_GETPAGES() must keep reqpage busy. It must unbusy all other successfully handled pages and put them on appropriate page queue(s). For example, VOP_GETPAGES() may either activate a page (if its wanted bit is set) or deactivate it (otherwise), and finally call vm_page_wakeup(9) to arouse any threads currently waiting for the page to be faulted in.

RETURN VALUES
If it successfully reads ma[reqpage], VOP_GETPAGES() returns VM_PAGER_OK; otherwise, VM_PAGER_ERROR. By convention, the return value of VOP_PUTPAGES() is rtvals[0].

SEE ALSO
vm_object_pip_wakeup(9), vm_page_free(9), vm_page_io_finish(9), vm_page_undirty(9), vm_page_wakeup(9), vnode(9)

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