page-pipe.h

#ifndef __CR_PAGE_PIPE_H__
#define __CR_PAGE_PIPE_H__

#include <sys/uio.h>
#include "common/list.h"

#define PAGE_ALLOC_COSTLY_ORDER 3 /* from the kernel source code */
struct kernel_pipe_buffer {
        struct page *page;
        unsigned int offset, len;
        const struct pipe_buf_operations *ops;
        unsigned int flags;
        unsigned long private;
};

/*
 * The kernel allocates the linear chunk of memory for pipe buffers.
 * Allocation of chunks with size more than PAGE_ALLOC_COSTLY_ORDER
 * fails very often, so we need to restrict the pipe capacity to not
 * allocate big chunks.
 */
#define PIPE_MAX_SIZE ((1 << PAGE_ALLOC_COSTLY_ORDER) * PAGE_SIZE /	\
			sizeof(struct kernel_pipe_buffer))

/* The number of pipes for one chunk */
#define NR_PIPES_PER_CHUNK 8

/*
 * page_pipe is a descriptor of task's virtual memory
 * with pipes, containing pages.
 *
 * A page-pipe may contain holes -- these are pagemap
 * entries without pages. Holes are stored in separate
 * array to optimize paged iovs feed into vmsplice --
 * they will be sent there in one go.
 *
 * A hole is a pagemap entry that doesn't have pages
 * in it, since they are present in previous (parent)
 * snapshot.
 *
 *
 * This page-pipe vs holes vs task vmem vs image layout
 * is described below.
 *
 * Task memory: (+ present, - not present pages)
 *    0  0  0    0     1      1   1
 *    0  3  6    B     1      8   C
 *    ---+++-----++++++-------++++----
 *
 * Page-pipe iovs:
 *
 *    bufs = 03:3,0B:6,18:4
 *    holes = <empty>
 *
 * The pagemap.img would purely contain page-pipe bufs.
 *
 * Pages image will contain pages at
 *
 *    03,04,05,0B,0C,0D,0E,0F,10,18,19,1A,1B
 *
 * stored one by one.
 *
 * Not let's imagine task touches some pages and its mem
 * looks like: (+ present, = old present, - non present)
 *
 *    0  0  0    0     11    11   1
 *    0  3  6    B     12    78   C
 *    ---==+-----====+++-----++===----
 *
 * (not new pages at 11 and 17 vaddrs)
 *
 * The new --snapshot'ed page-pipe would look like
 *
 *    bufs = 05:1,0F:3,17:2
 *    holes = 03:2,0B:4,19:3
 *
 * So the pagemap.img would look like
 *
 *    03:2:P,05:1,0B:4:P,0F:3,17:2,19:3:P
 *
 * (the page_xfer_dump_pages generates one)
 *
 * where P means "in parent", i.e. respective pages should
 * be looked up in the parent pagemap (not pages.img, but
 * the pagemap, and then the offset in previous pages.img
 * should be calculated, see the read_pagemap_page routine).
 *
 * New pages.img file would contain only pages for
 *
 *    05,0F,10,11,17,18
 */

struct page_pipe_buf {
	int p[2];		/* pipe with pages */
	unsigned int pipe_size;	/* how many pages can be fit into pipe */
	unsigned int pages_in;	/* how many pages are there */
	unsigned int nr_segs;	/* how many iov-s are busy */
	struct iovec *iov;	/* vaddr:len map */
	struct list_head l;	/* links into page_pipe->bufs */
};

struct page_pipe {
	unsigned int nr_pipes;	/* how many page_pipe_bufs in there */
	struct list_head bufs;	/* list of bufs */
	struct list_head free_bufs;	/* list of bufs */
	unsigned int nr_iovs;	/* number of iovs */
	unsigned int free_iov;	/* first free iov */
	struct iovec *iovs;	/* iovs. They are provided into create_page_pipe
				   and all bufs have their iov-s in there */

	unsigned int nr_holes;	/* number of holes allocated */
	unsigned int free_hole;	/* number of holes in use */
	struct iovec *holes;	/* holes */
	unsigned flags;		/* PP_FOO flags below */
};

#define PP_CHUNK_MODE	0x1	/* Restrict the maximum buffer size of pipes
				   and dump memory for a few iterations */
#define PP_COMPAT	0x2	/* Use compatible iovs (struct compat_iovec) */
#define PP_OWN_IOVS	0x4	/* create_page_pipe allocated IOVs memory */

struct page_pipe *create_page_pipe(unsigned int nr_segs, struct iovec *iovs, unsigned flags);
extern void destroy_page_pipe(struct page_pipe *p);
extern int page_pipe_add_page(struct page_pipe *p, unsigned long addr);
extern int page_pipe_add_hole(struct page_pipe *p, unsigned long addr);

extern void debug_show_page_pipe(struct page_pipe *pp);
void page_pipe_reinit(struct page_pipe *pp);

#endif /* __CR_PAGE_PIPE_H__ */