bigfile: Stub for virtmem

This will be the core of virtual memory subsystem. For now we just
define a structure to describe pages of memory and add utility to
allocate address space from OS.

bigfile/virtmem.c

+/* Wendelin.bigfile | Virtual memory
+ * Copyright (C) 2014-2015  Nexedi SA and Contributors.
+ *                          Kirill Smelkov <kirr@nexedi.com>
+ *
+ * This program is free software: you can Use, Study, Modify and Redistribute
+ * it under the terms of the GNU General Public License version 3, or (at your
+ * option) any later version, as published by the Free Software Foundation.
+ *
+ * You can also Link and Combine this program with other software covered by
+ * the terms of any of the Open Source Initiative approved licenses and Convey
+ * the resulting work. Corresponding source of such a combination shall include
+ * the source code for all other software used.
+ *
+ * This program is distributed WITHOUT ANY WARRANTY; without even the implied
+ * warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+ *
+ * See COPYING file for full licensing terms.
+ */
+
+#include <wendelin/bigfile/virtmem.h>
+#include <wendelin/bigfile/ram.h>
+
+#include <sys/mman.h>
+#include <errno.h>
+
+
+/*
+ * allocate virtual memory address space
+ * the pages are initially protected to prevent any access
+ *
+ * @addr    NULL - at anywhere,     !NULL - exactly there
+ * @return  !NULL - mapped there    NULL - error
+ */
+void *mem_valloc(void *addr, size_t len)
+{
+    void *a;
+    a = mmap(addr, len, PROT_NONE,
+            MAP_PRIVATE | MAP_ANONYMOUS
+            /* don't try to (pre-)allocate memory - just virtual address space */
+            | MAP_NORESERVE
+            | (addr ? MAP_FIXED : 0),
+            -1, 0);
+
+    if (a == MAP_FAILED)
+        a = NULL;
+
+    if (a && addr)
+        /* verify OS respected our MAP_FIXED request */
+        BUG_ON(a != addr);
+
+    return a;
+}
+
+
+/* like mem_valloc() but allocation must not fail */
+void *mem_xvalloc(void *addr, size_t len)
+{
+    void *a;
+    a = mem_valloc(addr, len);
+    BUG_ON(!a);
+    return a;
+}
+
+
+/********************
+ * Internal helpers *
+ ********************/
+
+static size_t page_size(const Page *page)
+{
+    return page->ramh->ram->pagesize;
+}
+
+void page_incref(Page *page)
+{
+    page->refcnt++;     // XXX atomically ?
+}
+
+void page_decref(Page *page)
+{
+    page->refcnt--;     // XXX atomically ?
+    BUG_ON(page->refcnt < 0);
+
+    // TODO if unused delete self && clear pagemap ?
+    // XXX  if dirty -> delete = not ok
+}
+
+void *page_mmap(Page *page, void *addr, int prot)
+{
+    RAMH *ramh = page->ramh;
+    // XXX better call ramh_mmap_page() without tinkering wih ramh_ops?
+    return ramh->ramh_ops->mmap_page(ramh, page->ramh_pgoffset, addr, prot);
+}

include/wendelin/bigfile/virtmem.h

+#ifndef _WENDELIN_BIGFILE_VIRTMEM_H_
+#define _WENDELIN_BIGFILE_VIRTMEM_H_
+
+/* Wendelin.bigfile | Virtual memory
+ * Copyright (C) 2014-2015  Nexedi SA and Contributors.
+ *                          Kirill Smelkov <kirr@nexedi.com>
+ *
+ * This program is free software: you can Use, Study, Modify and Redistribute
+ * it under the terms of the GNU General Public License version 3, or (at your
+ * option) any later version, as published by the Free Software Foundation.
+ *
+ * You can also Link and Combine this program with other software covered by
+ * the terms of any of the Open Source Initiative approved licenses and Convey
+ * the resulting work. Corresponding source of such a combination shall include
+ * the source code for all other software used.
+ *
+ * This program is distributed WITHOUT ANY WARRANTY; without even the implied
+ * warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+ *
+ * See COPYING file for full licensing terms.
+ */
+
+#include <stdint.h>
+#include <wendelin/list.h>
+
+typedef struct RAMH RAMH;
+
+
+/* Page - describes fixed-size item of physical RAM associated with content from file */
+enum PageState {
+    PAGE_EMPTY      = 0, /* file content has not been loaded yet */
+    PAGE_LOADED     = 1, /* file content has     been loaded and was not modified */
+    PAGE_DIRTY      = 2, /* file content has     been loaded and was     modified */
+};
+typedef enum PageState PageState;
+
+struct Page {
+    PageState   state;
+
+    /* wrt ram - associated with */
+    RAMH*       ramh;
+    pgoff_t     ramh_pgoffset;
+
+    /* in recently-used pages for ramh->ram (ram->lru_list -> _) */
+    struct list_head lru;
+
+    int     refcnt; /* each mapping in a vma counts here */
+};
+typedef struct Page Page;
+
+
+/************
+ * Internal *
+ ************/
+
+/* mmap page memory into address space
+ *
+ * @addr     NULL - mmap somewhere,    !NULL - mmap exactly there (MAP_FIXED)
+ * @return  !NULL - mmapped ok there,   NULL - error
+ *
+ * NOTE to unmap memory either
+ *
+ *      - use usual munmap(2), or
+ *      - mmap(2) something else in place of mmaped page memory.
+ */
+void *page_mmap(Page *page, void *addr, int prot);
+
+void page_incref(Page *page);
+void page_decref(Page *page);
+
+
+/* allocate virtual memory address space */
+void *mem_valloc(void *addr, size_t len);
+void *mem_xvalloc(void *addr, size_t len);
+
+#endif

setup.py

@@ -29,6 +29,7 @@ _bigfile = Extension('wendelin.bigfile._bigfile',
                 'bigfile/_bigfile.c',
                 'bigfile/pagefault.c',
                 'bigfile/pagemap.c',
+                'bigfile/virtmem.c',
                 'lib/bug.c',
                 'lib/utils.c',
             ],