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VOP_GETPAGES(9) Kernel Developer's Manual VOP_GETPAGES(9)

NAME

VOP_GETPAGES, VOP_PUTPAGESread 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 count, int sync, int *rtvals);

DESCRIPTION

The () 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
if the write should be synchronous.
rtvals
An array of VM system result codes indicating the status of each page written by ().
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 () 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 () 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_xunbusy(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_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.

December 16, 2015 Debian