VOP_GETPAGES
,
VOP_PUTPAGES
—
read or write VM pages from a file
#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);
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; control 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 indicate to the filesystem
that pages should be marked for fast reuse 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 feature, 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 feature, 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:
- The page was successfully written. The implementation must call
vm_page_undirty(9)
to mark the page as clean.
- 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).
- 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.
- The page could not be written because of an error on the underlying
storage medium or protocol.
- Treated identically to
VM_PAGER_ERROR
.
- 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 particular filesystem.
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].
vm_object_pip_wakeup(9),
vm_page_free(9),
vm_page_sunbusy(9),
vm_page_undirty(9),
vm_page_xunbusy(9),
vnode(9)
This manual page was written by
Doug Rabson
and then substantially rewritten by
Garrett Wollman.