lib/utils: Small C utilities we'll use

Like taking an exact integer log2, upcasting pointers for C-style
inheritance done in a Plan9 way, and wrappers to functions which should
never fail.

include/wendelin/utils.h

+#ifndef _WENDELIN_UTILS_H_
+#define _WENDELIN_UTILS_H_
+
+/* Wendelin. Miscellaneous utilities
+ * 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 <ccan/build_assert/build_assert.h>
+#include <stdlib.h>
+
+
+/* compile-time exact ilog2(x); x must be 2^k */
+#define BUILD_ILOG2_EXACT(x) (  \
+    /* check that only 1 bit set - then it will be exact */     \
+    BUILD_ASSERT_OR_ZERO(__builtin_popcount(x) == 1) +          \
+    __builtin_ctz(x)                                            \
+)
+
+/* runtime analog of BUILD_ILOG2_EXACT */
+unsigned ilog2_exact(unsigned x);
+
+
+/* upcast from ptr-to-embedded type to ptr-to-container
+ *
+ * ex:
+ *
+ *      struct base { ... };
+ *      struct child { ... struct base; ... };
+ *
+ *      struct base *pbase;
+ *      struct child *pchild = upcast(struct child *, pbase);
+ *
+ * TODO give error on invalid usage (so far only warning)
+ */
+#define upcast(ptype, ptr) ({                   \
+    ptype __child = NULL;                       \
+    /* implicit offsetof(child, base); gives only warning on incorrect usage */    \
+    typeof(ptr) __base = __child;               \
+    (ptype)                                     \
+        ( (char *)ptr - (uintptr_t)__base );    \
+})
+
+
+
+/* allocate zeroed memory */
+static inline
+void *zalloc(size_t size)
+{
+    return calloc(1, size);
+}
+
+
+/* should-not-fail helpers */
+void *xzalloc(size_t size);
+char *xstrdup(const char *s);
+void xclose(int fd);
+void xmunmap(void *addr, size_t len);
+void xmprotect(void *addr, size_t len, int prot);
+void xfallocate(int fd, int mode, off_t offset, off_t len);
+void xftruncate(int fd, off_t len);
+
+void xsigemptyset(sigset_t *set);
+void xsigaddset(sigset_t *set, int sig);
+void xpthread_sigmask(int how, const sigset_t *set, sigset_t *oldset);
+
+#endif

lib/utils.c

+/* Wendelin. Miscellaneous utilities
+ * 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/utils.h>
+#include <wendelin/bug.h>
+
+#include <sys/types.h>
+#include <sys/mman.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <string.h>
+#include <signal.h>
+
+
+/* ilog2 that must be exact */
+unsigned ilog2_exact(unsigned x)
+{
+    BUG_ON(__builtin_popcount(x) != 1);
+    return __builtin_ctz(x);
+}
+
+
+/* if allocating memory on DSO init or ram types registration fails, we have
+ * bigger problems */
+void *xzalloc(size_t size)
+{
+    void *addr;
+    addr = zalloc(size);
+    if (!addr)
+        BUGe();
+    return addr;
+}
+
+
+/* likewise */
+char *xstrdup(const char *s)
+{
+    char *d;
+    d = strdup(s);
+    if (!d)
+        BUGe();
+    return d;
+}
+
+
+/* closing correct fd on shmfs-like filesystem should be ok */
+void xclose(int fd)
+{
+    int err;
+    err = close(fd);
+    if (err)
+        BUGe();
+}
+
+/* unmapping memory should not fail, if it was previously mmaped ok */
+void xmunmap(void *addr, size_t len)
+{
+    int err;
+    BUG_ON(!addr);  /* munmap(2) does not catch this XXX why ? */
+    err = munmap(addr, len);
+    if (err)
+        BUGe();
+}
+
+/* changing protection to previously RW-mmaped memory should not fail */
+void xmprotect(void *addr, size_t len, int prot)
+{
+    int err;
+    err = mprotect(addr, len, prot);
+    if (err)
+        BUGe();
+}
+
+/* releasing memory with correct offset and len should not fail */
+void xfallocate(int fd, int mode, off_t offset, off_t len)
+{
+    int err;
+    err = fallocate(fd, mode, offset, len);
+    if (err)
+        BUGe();
+}
+
+/* truncating file to 0 size should be ok */
+void xftruncate(int fd, off_t len)
+{
+    int err;
+    err = ftruncate(fd, len);
+    if (err)
+        BUGe();
+}
+
+
+/* sig*set should not fail on any correct usage */
+void xsigemptyset(sigset_t *set)
+{
+    int err;
+    err = sigemptyset(set);
+    if (err)
+        BUGe();
+}
+
+void xsigaddset(sigset_t *set, int sig)
+{
+    int err;
+    err = sigaddset(set, sig);
+    if (err)
+        BUGe();
+}
+
+/* pthread_sigmask() should not fail on any correct usage */
+void xpthread_sigmask(int how, const sigset_t *set, sigset_t *oldset)
+{
+    int err;
+    err = pthread_sigmask(how, set, oldset);
+    if (err)
+        BUGe();
+}

setup.py

@@ -28,6 +28,7 @@ _bigfile = Extension('wendelin.bigfile._bigfile',
             sources = [
                 'bigfile/_bigfile.c',
                 'lib/bug.c',
+                'lib/utils.c',
             ],
             include_dirs = [
                 './include',