Release 0.13.0

native/atomic_file.h

@@ -0,0 +1,91 @@
+#ifndef HYPERDRM_ATOMIC_FILE_H
+#define HYPERDRM_ATOMIC_FILE_H
+#include <stdbool.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <string.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <sys/stat.h>
+#include <unistd.h>
+#ifndef ATOMIC_WRITE
+#define ATOMIC_WRITE write
+#endif
+#ifndef ATOMIC_SYNC
+#define ATOMIC_SYNC fsync
+#endif
+#ifndef ATOMIC_RENAME
+#define ATOMIC_RENAME renameat
+#endif
+typedef enum { SAVE_UNCHANGED, SAVE_DURABLE, SAVE_COMMITTED } SaveResult;
+/* Failure before rename preserves the previous file. After rename, a directory
+ * sync failure cannot truthfully be called a rollback: report committed with
+ * uncertain durability, so memory and disk never deliberately diverge. */
+static inline SaveResult atomic_replace(const char *path, const void *data, size_t length) {
+    char parent[512], temporary[544];
+    if (!path || !data || strlen(path) >= sizeof(parent))
+        return SAVE_UNCHANGED;
+    strcpy(parent, path);
+    char *slash = strrchr(parent, '/');
+    const char *name = slash ? strrchr(path, '/') + 1 : path;
+    if (!*name || !strcmp(name, ".") || !strcmp(name, ".."))
+        return SAVE_UNCHANGED;
+    if (slash) {
+        if (slash == parent)
+            slash[1] = 0;
+        else
+            *slash = 0;
+    } else
+        strcpy(parent, ".");
+    int dir = open(parent, O_RDONLY | O_DIRECTORY | O_NOFOLLOW | O_CLOEXEC);
+    if (dir < 0)
+        return SAVE_UNCHANGED;
+    struct stat existing;
+    int found = fstatat(dir, name, &existing, AT_SYMLINK_NOFOLLOW);
+    if ((found < 0 && errno != ENOENT) || (found == 0 && !S_ISREG(existing.st_mode)) ||
+        ATOMIC_SYNC(dir) != 0) {
+        close(dir);
+        return SAVE_UNCHANGED;
+    }
+    if (snprintf(temporary, sizeof(temporary), "%s/.%s.tmp.XXXXXX", parent, name) >=
+        (int)sizeof(temporary)) {
+        close(dir);
+        return SAVE_UNCHANGED;
+    }
+    int fd = mkstemp(temporary);
+    if (fd < 0) {
+        close(dir);
+        return SAVE_UNCHANGED;
+    }
+    fcntl(fd, F_SETFD, FD_CLOEXEC);
+    const unsigned char *bytes = data;
+    size_t written = 0;
+    bool ok = true;
+    while (written < length) {
+        ssize_t n = ATOMIC_WRITE(fd, bytes + written, length - written);
+        if (n < 0 && errno == EINTR)
+            continue;
+        if (n <= 0) {
+            ok = false;
+            break;
+        }
+        written += (size_t)n;
+    }
+    if (ok)
+        ok = ATOMIC_SYNC(fd) == 0;
+    if (close(fd) != 0)
+        ok = false;
+    const char *tempname = strrchr(temporary, '/') + 1;
+    if (ok)
+        ok = ATOMIC_RENAME(dir, tempname, dir, name) == 0;
+    SaveResult result = SAVE_UNCHANGED;
+    if (ok) {
+        result = ATOMIC_SYNC(dir) == 0 ? SAVE_DURABLE : SAVE_COMMITTED;
+        if (result == SAVE_COMMITTED)
+            fprintf(stderr, "Preference committed; directory sync failed\n");
+    } else
+        unlinkat(dir, tempname, 0);
+    close(dir);
+    return result;
+}
+#endif