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

     VOP_GETPAGES, VOP_PUTPAGES	-- read	or write VM pages from a file

     #include <sys/param.h>
     #include <sys/vnode.h>
     #include <vm/vm.h>

     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);

     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 length of the	ma array.

	      The number of bytes that should be written from the pages	of the

     flags    A	bitfield of flags affecting the	function operation.  If
	      VM_PAGER_PUT_SYNC	is set,	the write should be synchronous; con-
	      trol must	not be returned	to the caller until after the write is
	      finished.	 If VM_PAGER_PUT_INVAL is set, the pages are to	be in-
	      validated	after being written.  If VM_PAGER_PUT_NOREUSE is 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_OK is set,
	      writes may be delayed, so	that related writes can	be coalesced
	      for efficiency, e.g., using the clustering mechanism of the buf-
	      fer cache.

     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 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 VOP_GETPAGES(), all 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 particu-
     lar filesystem.

     If	it successfully	reads all pages	in ma, VOP_GETPAGES() returns
     VM_PAGER_OK; otherwise, it	returns	VM_PAGER_ERROR.	 By convention,	the
     return value of VOP_PUTPAGES() is rtvals[0].

     vm_object_pip_wakeup(9), vm_page_free(9), vm_page_sunbusy(9),
     vm_page_undirty(9), vm_page_xunbusy(9), vnode(9)

     This manual page was written by Doug Rabson and then substantially
     rewritten by
     Garrett Wollman.

BSD				 June 29, 2019				   BSD


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