scripts: add portable mkswap.c extracted from BusyBox

Signed-off-by: Park Ju Hyung <[email protected]>

Author: arter97

Diff for: scripts/mkswap.c

@@ -0,0 +1,123 @@
+/*
+ * mkswap.c - format swap device (Linux v1 only)
+ *
+ * Copyright 2006 Rob Landley <[email protected]>
+ *
+ * Licensed under GPLv2
+ */
+
+#include <stdio.h>
+#include <stdint.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+
+/* from Linux 2.6.23 */
+/*
+ * Magic header for a swap area. ... Note that the first
+ * kilobyte is reserved for boot loader or disk label stuff.
+ */
+struct swap_header_v1 {
+/*	char     bootbits[1024];    Space for disklabel etc. */
+	uint32_t version;        /* second kbyte, word 0 */
+	uint32_t last_page;      /* 1 */
+	uint32_t nr_badpages;    /* 2 */
+	char     sws_uuid[16];   /* 3,4,5,6 */
+	char     sws_volume[16]; /* 7,8,9,10 */
+	uint32_t padding[117];   /* 11..127 */
+	uint32_t badpages[1];    /* 128 */
+	/* total 129 32-bit words in 2nd kilobyte */
+} __attribute__((__may_alias__));
+
+#define NWORDS 129
+#define COMMON_BUFSIZE 1024
+
+static struct swap_header_v1 *hdr;
+
+struct BUG_sizes {
+	char swap_header_v1_wrong[sizeof(*hdr)  != (NWORDS * 4) ? -1 : 1];
+	char bufsiz1_is_too_small[COMMON_BUFSIZE < (NWORDS * 4) ? -1 : 1];
+};
+
+/* Stored without terminating NUL */
+static const char SWAPSPACE2[sizeof("SWAPSPACE2")-1] __attribute__((aligned(1))) = "SWAPSPACE2";
+
+static loff_t get_volume_size_in_bytes(int fd)
+{
+	loff_t result;
+
+	/* more portable than BLKGETSIZE[64] */
+	result = lseek(fd, 0, SEEK_END);
+
+	lseek(fd, 0, SEEK_SET);
+
+	/* Prevent things like this:
+	 * $ dd if=/dev/zero of=foo count=1 bs=1024
+	 * $ mkswap foo
+	 * Setting up swapspace version 1, size = 18446744073709548544 bytes
+	 *
+	 * Picked 16k arbitrarily: */
+	if (result < 16*1024) {
+		fprintf(stderr, "image is too small\n");
+		exit(1);
+	}
+
+	return result;
+}
+
+int main(int argc, char **argv)
+{
+	int fd;
+	int pagesize;
+	off_t len;
+	const char *label = "";
+
+	if (argc < 2) {
+		fprintf(stderr, "Usage: %s /path/to/swapfile\n", argv[0]);
+		exit(1);
+	}
+
+	fd = open(argv[1], O_WRONLY);
+	if (fd == -1) {
+		perror("Failed to open file");
+		exit(1);
+	}
+
+	/* Figure out how big the device is */
+	len = get_volume_size_in_bytes(fd);
+	pagesize = getpagesize();
+	len -= pagesize;
+
+	hdr = (struct swap_header_v1*)calloc(1, 1024);
+
+	/* Announce our intentions */
+	printf("Setting up swapspace version 1, size = %jd bytes\n", (intmax_t)len);
+
+	/* hdr is zero-filled so far. Clear the first kbyte, or else
+	 * mkswap-ing former FAT partition does NOT erase its signature.
+	 *
+	 * util-linux-ng 2.17.2 claims to erase it only if it does not see
+	 * a partition table and is not run on whole disk. -f forces it.
+	 */
+	write(fd, hdr, 1024);
+
+	/* Fill the header. */
+	hdr->version = 1;
+	hdr->last_page = (uint32_t)(len / pagesize);
+
+	strncpy(hdr->sws_volume, label, 16);
+
+	/* Write the header.  Sync to disk because some kernel versions check
+	 * signature on disk (not in cache) during swapon. */
+	write(fd, hdr, NWORDS * 4);
+	lseek(fd, pagesize - 10, SEEK_SET);
+	write(fd, SWAPSPACE2, 10);
+	fsync(fd);
+
+	close(fd);
+
+	return 0;
+}