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VOP_GETPAGES(9)
VOP_GETPAGES(9) BSD Kernel Developer's Manual 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 *rbehind,
int *rahead);
int
VOP_PUTPAGES(struct vnode *vp, vm_page_t *ma, int bytecount, int flags,
int *rtvals);
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 length of the ma array.
bytecount
The number of bytes that should be written from the pages of the
array.
flags A bitfield of flags affecting the function operation. If
VM_PAGER_PUT_SYNC is set, the write should be synchronous; con‐
trol must not be returned to the caller until after the write is
finished. If VM_PAGER_PUT_INVAL is set, the pages are to be
invalidated after being written. If VM_PAGER_PUT_NOREUSE is
set, the I/O performed should set the IO_NOREUSE flag, to indi‐
cate to the filesystem that pages should be marked for fast re‐
use if needed. This could occur via a call to
vm_page_deactivate_noreuse(9), which puts such pages onto the
head of the inactive queue. If VM_PAGER_CLUSTER_OK is set,
writes may be performed asynchronously, so that related writes
can be coalesced for efficiency, e.g., using the clustering
mechanism of the buffer cache.
rtvals An array of VM system result codes indicating the status of each
page written by VOP_PUTPAGES().
rbehind Optional pointer to integer specifying number of pages to be
read behind, if possible. If the filesystem supports that fea‐
ture, number of actually read pages is reported back, otherwise
zero is returned.
rahead Optional pointer to integer specifying number of pages to be
read ahead, if possible. If the filesystem supports that fea‐
ture, number of actually read pages is reported back, otherwise
zero is returned.
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_sunbusy(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 must populate and validate all requested pages
in order to return success. It 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. Upon
entry to VOP_GETPAGES(), all pages in ma are busied exclusively. Upon
successful return, the pages must all be busied exclusively as well, but
pages may be unbusied during processing. The filesystem is responsible
for activating paged-out pages, but this does not necessarily need to be
done within VOP_GETPAGES() depending on the architecture of the particu‐
lar filesystem.
RETURN VALUES
If it successfully reads all pages in ma, VOP_GETPAGES() returns
VM_PAGER_OK; otherwise, it returns 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_sunbusy(9),
vm_page_undirty(9), vm_page_xunbusy(9), vnode(9)
AUTHORS
This manual page was written by Doug Rabson and then substantially
rewritten by
Garrett Wollman.
BSD May 7, 2017 BSD