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

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 fea-
	      ture, 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	fea-
	      ture, 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 ba-
     sis 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	suc-
     ceeds, VOP_GETPAGES() must	set the	valid bits appropriately.
     VOP_GETPAGES() must keep reqpage busy.  It	must unbusy all	other success-
     fully handled pages and put them on appropriate page queue(s).  For exam-
     ple, 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.

BSD			       December	16, 2015			   BSD

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUES | SEE ALSO | AUTHORS

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