swapon: Do not overwrite Linux swap header

Reviewed by: imp, jhb
Pull Request: https://github.com/freebsd/freebsd-src/pull/1084

sbin/swapon/Makefile

@@ -6,6 +6,8 @@ LINKS=	${BINDIR}/swapon ${BINDIR}/swapoff
 LINKS+=	${BINDIR}/swapon ${BINDIR}/swapctl
 MLINKS=	swapon.8 swapoff.8
 MLINKS+=swapon.8 swapctl.8
+SRCS=	swapon.c swaplinux.c
+HDRS+=	extern.h
 
 LIBADD=	util
 

sbin/swapon/extern.h

@@ -0,0 +1,5 @@
+/*-
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+int is_linux_swap(const char *);

sbin/swapon/swaplinux.c

@@ -0,0 +1,66 @@
+/*-
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+#include <fcntl.h>
+#include <err.h>
+#include <stdint.h>
+#include <string.h>
+#include <unistd.h>
+
+#include "extern.h"
+
+/*
+ * Definitions and structure taken from
+ * https://github.com/util-linux/util-linux/blob/master/include/swapheader.h
+ */
+
+#define SWAP_VERSION 1
+#define SWAP_UUID_LENGTH 16
+#define SWAP_LABEL_LENGTH 16
+#define SWAP_SIGNATURE "SWAPSPACE2"
+#define SWAP_SIGNATURE_SZ (sizeof(SWAP_SIGNATURE) - 1)
+
+struct swap_header_v1_2 {
+	char	      bootbits[1024];    /* Space for disklabel etc. */
+	uint32_t      version;
+	uint32_t      last_page;
+	uint32_t      nr_badpages;
+	unsigned char uuid[SWAP_UUID_LENGTH];
+	char	      volume_name[SWAP_LABEL_LENGTH];
+	uint32_t      padding[117];
+	uint32_t      badpages[1];
+};
+
+typedef union {
+	struct swap_header_v1_2 header;
+	struct {
+		uint8_t	reserved[4096 - SWAP_SIGNATURE_SZ];
+		char	signature[SWAP_SIGNATURE_SZ];
+	} tail;
+} swhdr_t;
+
+#define sw_version	header.version
+#define sw_volume_name	header.volume_name
+#define sw_signature	tail.signature
+
+int
+is_linux_swap(const char *name)
+{
+	uint8_t buf[4096];
+	swhdr_t *hdr = (swhdr_t *) buf;
+	int fd;
+
+	fd = open(name, O_RDONLY);
+	if (fd == -1)
+		return (-1);
+
+	if (read(fd, buf, 4096) != 4096) {
+		close(fd);
+		return (-1);
+	}
+	close(fd);
+
+	return (hdr->sw_version == SWAP_VERSION &&
+	    !memcmp(hdr->sw_signature, SWAP_SIGNATURE, SWAP_SIGNATURE_SZ));
+}

sbin/swapon/swapon.c

@@ -54,10 +54,15 @@
 #include <string.h>
 #include <unistd.h>
 
+#include "extern.h"
+
+#define _PATH_GNOP	"/sbin/gnop"
+
 static void usage(void) __dead2;
 static const char *swap_on_off(const char *, int, char *);
 static const char *swap_on_off_gbde(const char *, int);
 static const char *swap_on_off_geli(const char *, char *, int);
+static const char *swap_on_off_linux(const char *, int);
 static const char *swap_on_off_md(const char *, char *, int);
 static const char *swap_on_off_sfile(const char *, int);
 static void swaplist(int, int, int);
@@ -250,8 +255,13 @@ swap_on_off(const char *name, int doingall, char *mntops)
 		return (swap_on_off_geli(name, mntops, doingall));
 	}
 
-	/* Swap on special file. */
 	free(basebuf);
+
+	/* Linux swap */
+	if (is_linux_swap(name))
+		return (swap_on_off_linux(name, doingall));
+
+	/* Swap on special file. */
 	return (swap_on_off_sfile(name, doingall));
 }
 
@@ -466,6 +476,48 @@ swap_on_off_geli(const char *name, char *mntops, int doingall)
 	return (swap_on_off_sfile(name, doingall));
 }
 
+static const char *
+swap_on_off_linux(const char *name, int doingall)
+{
+	const char *ret;
+	char *nopname;
+	size_t nopnamelen;
+	int error;
+
+	if (which_prog == SWAPON) {
+		/* Skip the header for Linux swap partitions */
+		error = run_cmd(NULL, "%s create -o 4096 %s", _PATH_GNOP,
+		    name);
+		if (error) {
+			warnx("gnop (create) error: %s", name);
+			return (NULL);
+		}
+	}
+
+	/* Append ".nop" to name */
+	nopnamelen = strlen(name) + sizeof(".nop");
+	nopname = (char *) malloc(nopnamelen);
+	if (nopname == NULL)
+		err(1, "malloc()");
+	(void)strlcpy(nopname, name, nopnamelen);
+	(void)strlcat(nopname, ".nop", nopnamelen);
+
+	ret = swap_on_off_sfile(nopname, doingall);
+
+	if (which_prog == SWAPOFF) {
+		error = run_cmd(NULL, "%s destroy %s", _PATH_GNOP, nopname);
+		if (error) {
+			warnx("gnop (destroy) error: %s", name);
+			free(nopname);
+			return (NULL);
+		}
+	}
+
+	free(nopname);
+
+	return (ret);
+}
+
 static const char *
 swap_on_off_md(const char *name, char *mntops, int doingall)
 {