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.

Debian                                         September 27, 2003                                VOP_GETPAGES(9)