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 count, int sync, 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 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().

       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:

       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 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.

Debian                                          December 16, 2015                                VOP_GETPAGES(9)