|VOP_GETPAGES(9)||Kernel Developer's Manual||VOP_GETPAGES(9)|
VOP_PUTPAGES — read or write
VM pages from a file
VOP_GETPAGES(struct vnode *vp,
vm_page_t *ma, int count,
int *rbehind, int *rahead);
VOP_PUTPAGES(struct vnode *vp,
vm_page_t *ma, int bytecount,
int flags, int *rtvals);
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:
- The file to access.
- Pointer to the first element of an array of pages representing a contiguous region of the file to be read or written.
- The length of the ma array.
- The number of bytes that should be written from the pages of the array.
- A bitfield of flags affecting the function operation. If
VM_PAGER_PUT_SYNCis set, the write should be synchronous; control must not be returned to the caller until after the write is finished. If
VM_PAGER_PUT_INVALis set, the pages are to be invalidated after being written. If
VM_PAGER_PUT_NOREUSEis 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_OKis set, writes may be delayed, so that related writes can be coalesced for efficiency, e.g., using the clustering mechanism of the buffer cache.
- An array of VM system result codes indicating the status of each page
- 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.
- 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
method is returned on a page-by-page basis in the array
rtvals. The possible status values are as
- 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
- The page was not handled by this request.
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
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
If it successfully reads all pages in ma,
VM_PAGER_OK; otherwise, it returns
VM_PAGER_ERROR. By convention, the return value of
This manual page was written by Doug
Rabson and then substantially rewritten by
|June 29, 2019||Debian|