page-pipe.c

#include <unistd.h>
#include <fcntl.h>

#undef LOG_PREFIX
#define LOG_PREFIX "page-pipe: "

#include "util.h"
#include "page-pipe.h"

static int page_pipe_grow(struct page_pipe *pp)
{
	struct page_pipe_buf *ppb;

	pr_debug("Will grow page pipe (iov off is %u)\n", pp->free_iov);

	ppb = xmalloc(sizeof(*ppb));
	if (!ppb)
		return -1;

	if (pipe(ppb->p)) {
		xfree(ppb);
		pr_perror("Can't make pipe for page-pipe");
		return -1;
	}

	ppb->pipe_size = fcntl(ppb->p[0], F_GETPIPE_SZ, 0) / PAGE_SIZE;
	ppb->pages_in = 0;
	ppb->nr_segs = 0;
	ppb->iov = &pp->iovs[pp->free_iov];

	list_add_tail(&ppb->l, &pp->bufs);
	pp->nr_pipes++;

	return 0;
}

struct page_pipe *create_page_pipe(unsigned int nr_segs, struct iovec *iovs)
{
	struct page_pipe *pp;

	pr_debug("Create page pipe for %u segs\n", nr_segs);

	pp = xmalloc(sizeof(*pp));
	if (pp) {
		pp->nr_pipes = 0;
		INIT_LIST_HEAD(&pp->bufs);
		pp->nr_iovs = nr_segs;
		pp->iovs = iovs;
		pp->free_iov = 0;

		pp->nr_holes = 0;
		pp->free_hole = 0;
		pp->holes = NULL;

		if (page_pipe_grow(pp))
			return NULL;
	}

	return pp;
}

void destroy_page_pipe(struct page_pipe *pp)
{
	struct page_pipe_buf *ppb, *n;

	pr_debug("Killing page pipe\n");

	list_for_each_entry_safe(ppb, n, &pp->bufs, l) {
		close(ppb->p[0]);
		close(ppb->p[1]);
		xfree(ppb);
	}

	xfree(pp);
}

#define PPB_IOV_BATCH	8

static inline int try_add_page_to(struct page_pipe *pp, struct page_pipe_buf *ppb,
		unsigned long addr)
{
	struct iovec *iov;

	if (ppb->pages_in == ppb->pipe_size) {
		int ret;

		ret = fcntl(ppb->p[0], F_SETPIPE_SZ, (ppb->pipe_size * PAGE_SIZE) << 1);
		if (ret < 0)
			return 1; /* need to add another buf */

		ret /= PAGE_SIZE;
		BUG_ON(ret < ppb->pipe_size);

		pr_debug("Grow pipe %x -> %x\n", ppb->pipe_size, ret);
		ppb->pipe_size = ret;
	}

	if (ppb->nr_segs) {
		/* can existing iov accumulate the page? */
		iov = &ppb->iov[ppb->nr_segs - 1];
		if ((unsigned long)iov->iov_base + iov->iov_len == addr) {
			iov->iov_len += PAGE_SIZE;
			goto out;
		}

		if (ppb->nr_segs == UIO_MAXIOV)
			/* XXX -- shrink pipe back? */
			return 1;
	}

	pr_debug("Add iov to page pipe (%u iovs, %u/%u total)\n",
			ppb->nr_segs, pp->free_iov, pp->nr_iovs);
	ppb->iov[ppb->nr_segs].iov_base = (void *)addr;
	ppb->iov[ppb->nr_segs].iov_len = PAGE_SIZE;
	ppb->nr_segs++;
	pp->free_iov++;
	BUG_ON(pp->free_iov > pp->nr_iovs);
out:
	ppb->pages_in++;
	return 0;
}

static inline int try_add_page(struct page_pipe *pp, unsigned long addr)
{
	BUG_ON(list_empty(&pp->bufs));
	return try_add_page_to(pp, list_entry(pp->bufs.prev, struct page_pipe_buf, l), addr);
}

int page_pipe_add_page(struct page_pipe *pp, unsigned long addr)
{
	int ret;

	ret = try_add_page(pp, addr);
	if (ret <= 0)
		return ret;

	ret = page_pipe_grow(pp);
	if (ret < 0)
		return ret;

	ret = try_add_page(pp, addr);
	BUG_ON(ret > 0);
	return ret;
}

#define PP_HOLES_BATCH	32

int page_pipe_add_hole(struct page_pipe *pp, unsigned long addr)
{
	struct iovec *iov;

	if (pp->free_hole >= pp->nr_holes) {
		pp->holes = xrealloc(pp->holes,
				(pp->nr_holes + PP_HOLES_BATCH) * sizeof(struct iovec));
		if (!pp->holes)
			return -1;

		pp->nr_holes += PP_HOLES_BATCH;
	}

	if (pp->free_hole) {
		iov = &pp->holes[pp->free_hole - 1];
		if ((unsigned long)iov->iov_base + iov->iov_len == addr) {
			iov->iov_len += PAGE_SIZE;
			goto out;
		}
	}

	iov = &pp->holes[pp->free_hole];
	iov->iov_base = (void *)addr;
	iov->iov_len = PAGE_SIZE;
	pp->free_hole++;
out:
	return 0;
}

void debug_show_page_pipe(struct page_pipe *pp)
{
	struct page_pipe_buf *ppb;
	int i;
	struct iovec *iov;

	if (log_get_loglevel() < LOG_DEBUG)
		return;

	pr_debug("Page pipe:\n");
	pr_debug("* %u pipes %u/%u iovs:\n",
			pp->nr_pipes, pp->free_iov, pp->nr_iovs);
	list_for_each_entry(ppb, &pp->bufs, l) {
		pr_debug("\tbuf %u pages, %u iovs:\n",
				ppb->pages_in, ppb->nr_segs);
		for (i = 0; i < ppb->nr_segs; i++) {
			iov = &ppb->iov[i];
			pr_debug("\t\t%p %zu\n", iov->iov_base, iov->iov_len / PAGE_SIZE);
		}
	}

	pr_debug("* %u holes:\n", pp->free_hole);
	for (i = 0; i < pp->free_hole; i++) {
		iov = &pp->holes[i];
		pr_debug("\t%p %zu\n", iov->iov_base, iov->iov_len / PAGE_SIZE);
	}
}