page-pipe: Introduce object to collect pages within

The page-pipe is an object, that can accumulate pages inside it. It
consists of list of page-pipe-bufs, which in turn has a pipa, an
array of iovecs that describe the pages' locations and some stats.

Users of it are supposed to vmsplice pages into pipes to accumulate
then for later use, and vmsplice them from pipes when required.
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

Makefile.crtools

@@ -40,6 +40,7 @@ obj-y	+= protobuf.o
 obj-y	+= tty.o
 obj-y	+= cr-exec.o
 obj-y	+= file-lock.o
+obj-y	+= page-pipe.o
 
 ifneq ($(MAKECMDGOALS),clean)
 incdeps := y

include/page-pipe.h

+#ifndef __CR_PAGE_PIPE_H__
+#define __CR_PAGE_PIPE_H__
+#include <sys/uio.h>
+#include "list.h"
+
+struct page_pipe_buf {
+	int p[2];
+	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;
+	struct list_head l;
+};
+
+struct page_pipe {
+	unsigned int nr_pipes;
+	struct list_head bufs;
+	unsigned int nr_iovs;
+	unsigned int free_iov;
+	struct iovec *iovs;
+};
+
+struct page_pipe *create_page_pipe(unsigned int nr, struct iovec *);
+void destroy_page_pipe(struct page_pipe *p);
+int page_pipe_add_page(struct page_pipe *p, unsigned long addr);
+int page_pipe_iterate_pages(struct page_pipe *p,
+		int (*fn)(int rpipe, unsigned long addr, void *), void *);
+#endif

page-pipe.c

+#include <unistd.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)) {
+		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;
+
+		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(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 -- shink 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;
+}
+
+static int page_buf_iterate(struct page_pipe_buf *ppb,
+		int (*fn)(int rpipe, unsigned long addr, void *), void *a)
+{
+	unsigned int pg;
+	unsigned long addr, seg_end;
+	struct iovec *iov;
+
+	pr_debug("Iterate ppb of %u pages, %u segs\n", ppb->pages_in, ppb->nr_segs);
+
+	iov = &ppb->iov[0];
+	addr = (unsigned long)iov->iov_base;
+	seg_end = addr + iov->iov_len;
+
+	for (pg = 0; pg < ppb->pages_in; pg++) {
+		int ret;
+
+		if (addr >= seg_end) {
+			iov++;
+			BUG_ON(iov - ppb->iov >= ppb->nr_segs);
+			addr = (unsigned long)iov->iov_base;
+			seg_end = addr + iov->iov_len;
+		}
+
+		ret = fn(ppb->p[0], addr, a);
+		if (ret)
+			return ret;
+
+		addr += PAGE_SIZE;
+	}
+
+	return 0;
+}
+
+int page_pipe_iterate_pages(struct page_pipe *pp,
+		int (*fn)(int rpipe, unsigned long addr, void *), void *a)
+{
+	int ret = 0;
+	struct page_pipe_buf *ppb;
+
+	pr_debug("Iterate pp\n");
+
+	list_for_each_entry(ppb, &pp->bufs, l) {
+		ret = page_buf_iterate(ppb, fn, a);
+		if (ret)
+			break;
+	}
+
+	pr_debug("Done iteration\n");
+
+	return ret;
+}