add page

src/page.c

@@ -0,0 +1,38 @@
+// page.c
+// 管理文件中的空闲块
+
+#define _GNU_SOURCE /* See feature_test_macros(7) */
+
+#include <stdint.h>
+#include <unistd.h>
+#include <fcntl.h>
+#include <sys/mman.h>
+
+#include "../include/binary.h"
+#include "../include/page.h"
+
+uint8_t nullpage[PAGESZ];
+
+void* alloc_page(int fd) {
+    uint64_t ptr, prev_ptr = 8;
+    void* page;
+    if(lseek(fd, 8, SEEK_SET) < 0) return EOF;
+    // 对于 page，只关心位于第一页 8~15 字节的 ptr of unused blk
+    readle64(fd, ptr);
+    while(ptr) {
+        if(!(ptr%PAGESZ)) { // 找到符合要求的页
+            page = mmap(NULL, PAGESZ, PROT_READ|PROT_WRITE, MAP_PRIVATE, fd, ptr);
+            if(page < 0) return page;
+            if(lseek(fd, prev_ptr, SEEK_SET) < 0) return EOF;
+            write(fd, page, 8); // 从空闲块链表移除本块
+            return page;
+        }
+        prev_ptr = ptr;
+        if(lseek(fd, ptr, SEEK_SET) < 0) return EOF;
+        readle64(fd, ptr);
+    }
+    ptr = lseek(fd, 0, SEEK_END);
+    if(ptr < 0 || !(ptr%PAGESZ)) return EOF;
+    if(write(fd, nullpage, PAGESZ) != PAGESZ) return EOF;
+    return mmap(NULL, PAGESZ, PROT_READ|PROT_WRITE, MAP_PRIVATE, fd, ptr);
+}