libfdisk: add API to control signatures wiping

Now libfdisk warns if another filesystem/RAID/PT signature is detected
on the device. It seems better and user-friendly to make it possible to
wipe the signatures when we write a new disk label to the device.

This patch adds to the library API

	fdisk_enable_wipe()
	fdisk_has_wipe()
	fdisk_get_collision()

to control this new feature. The device modification is done by
libblkid (the same we use in some mkfs-like utils).

Signed-off-by: Karel Zak <kzak@redhat.com>

libfdisk/docs/libfdisk-sections.txt

@@ -293,7 +293,9 @@ fdisk_deassign_device
 fdisk_enable_bootbits_protection
 fdisk_enable_details
 fdisk_enable_listonly
+fdisk_enable_wipe
 fdisk_get_alignment_offset
+fdisk_get_collision
 fdisk_get_devfd
 fdisk_get_devname
 fdisk_get_first_lba
@@ -313,6 +315,7 @@ fdisk_get_unit
 fdisk_get_units_per_sector
 fdisk_has_label
 fdisk_has_protected_bootbits
+fdisk_has_wipe
 fdisk_is_details
 fdisk_is_labeltype
 fdisk_is_listonly

libfdisk/src/context.c

@@ -334,6 +334,50 @@ int fdisk_enable_bootbits_protection(struct fdisk_context *cxt, int enable)
 	return 0;
 }
 
+/**
+ * fdisk_enable_wipe
+ * @cxt: fdisk context
+ * @enable: 1 or 0
+ *
+ * The library removes all filesystem/RAID signatures before write PT. This is
+ * no-op if any collision has not been detected by fdisk_assign_device(). See
+ * fdisk_has_collision(). The default is not wipe a device.
+ *
+ * Returns: 0 on success, < 0 on error.
+ */
+int fdisk_enable_wipe(struct fdisk_context *cxt, int enable)
+{
+	if (!cxt)
+		return -EINVAL;
+	cxt->wipe_device = enable ? 1 : 0;
+	return 0;
+}
+
+/**
+ * fdisk_has_wipe
+ * @cxt: fdisk context
+ *
+ * Returns the current wipe setting. See fdisk_enable_wipe().
+ *
+ * Returns: 0 on success, < 0 on error.
+ */
+int fdisk_has_wipe(struct fdisk_context *cxt)
+{
+	return cxt && cxt->wipe_device;
+}
+
+
+/**
+ * fdisk_get_collision
+ * @cxt: fdisk context
+ *
+ * Returns: name of the filesystem or RAID detected on the device or NULL.
+ */
+const char *fdisk_get_collision(struct fdisk_context *cxt)
+{
+	return cxt->collision;
+}
+
 /**
  * fdisk_get_npartitions:
  * @cxt: context
@@ -427,6 +471,9 @@ static void reset_context(struct fdisk_context *cxt)
 	free(cxt->dev_path);
 	cxt->dev_path = NULL;
 
+	free(cxt->collision);
+	cxt->collision = NULL;
+
 	cxt->dev_fd = -1;
 	cxt->firstsector = NULL;
 	cxt->firstsector_bufsz = 0;
@@ -445,18 +492,15 @@ static void reset_context(struct fdisk_context *cxt)
  *
  * Returns: 0 if nothing found, < 0 on error, 1 if found a signature
  */
-static int warn_wipe(struct fdisk_context *cxt)
+static int check_collisions(struct fdisk_context *cxt)
 {
 #ifdef HAVE_LIBBLKID
-	blkid_probe pr;
-#endif
 	int rc = 0;
+	blkid_probe pr;
 
 	assert(cxt);
+	assert(cxt->dev_fd >= 0);
 
-	if (fdisk_has_label(cxt) || cxt->dev_fd < 0)
-		return -EINVAL;
-#ifdef HAVE_LIBBLKID
 	DBG(CXT, ul_debugobj(cxt, "wipe check: initialize libblkid prober"));
 
 	pr = blkid_new_probe();
@@ -478,18 +522,48 @@ static int warn_wipe(struct fdisk_context *cxt)
 
 		if (blkid_probe_lookup_value(pr, "TYPE", &name, 0) == 0 ||
 		    blkid_probe_lookup_value(pr, "PTTYPE", &name, 0) == 0) {
-			fdisk_warnx(cxt, _(
-				"%s: device contains a valid '%s' signature; it is "
-				"strongly recommended to wipe the device with "
-				"wipefs(8) if this is unexpected, in order to "
-				"avoid possible collisions"), cxt->dev_path, name);
-			rc = 1;
+			cxt->collision = strdup(name);
+			if (!cxt->collision)
+				rc = -ENOMEM;
 		}
 	}
 
 	blkid_free_probe(pr);
-#endif
 	return rc;
+#elif
+	return 0;
+#endif
+}
+
+int fdisk_wipe_collisions(struct fdisk_context *cxt)
+{
+#ifdef HAVE_LIBBLKID
+	blkid_probe pr;
+	int rc;
+
+	assert(cxt);
+	assert(cxt->dev_fd >= 0);
+
+	DBG(CXT, ul_debugobj(cxt, "wipe: initialize libblkid prober"));
+
+	pr = blkid_new_probe();
+	if (!pr)
+		return -ENOMEM;
+	rc = blkid_probe_set_device(pr, cxt->dev_fd, 0, 0);
+	if (rc)
+		return rc;
+
+	blkid_probe_enable_superblocks(pr, 1);
+	blkid_probe_set_superblocks_flags(pr, BLKID_SUBLKS_MAGIC);
+	blkid_probe_enable_partitions(pr, 1);
+	blkid_probe_set_partitions_flags(pr, BLKID_PARTS_MAGIC);
+
+	while (blkid_do_probe(pr) == 0)
+		blkid_do_wipe(pr, FALSE);
+
+	blkid_free_probe(pr);
+#endif
+	return 0;
 }
 
 /**
@@ -564,8 +638,8 @@ int fdisk_assign_device(struct fdisk_context *cxt,
 
 	/* warn about obsolete stuff on the device if we aren't in
 	 * list-only mode and there is not PT yet */
-	if (!fdisk_is_listonly(cxt) && !fdisk_has_label(cxt))
-		warn_wipe(cxt);
+	if (!fdisk_is_listonly(cxt) && !fdisk_has_label(cxt) && check_collisions(cxt) < 0)
+		goto fail;
 
 	DBG(CXT, ul_debugobj(cxt, "initialized for %s [%s]",
 			      fname, readonly ? "READ-ONLY" : "READ-WRITE"));

libfdisk/src/fdiskP.h

@@ -355,8 +355,11 @@ struct fdisk_context {
 		     display_in_cyl_units : 1,	/* for obscure labels */
 		     display_details : 1,	/* expert display mode */
 		     protect_bootbits : 1,	/* don't zeroize fll irst sector */
+		     wipe_device : 1,		/* wipe device before write */
 		     listonly : 1;		/* list partition, nothing else */
 
+	char *collision;			/* name of already existing FS/PT */
+
 	int sizeunit;				/* SIZE fields, FDISK_SIZEUNIT_* */
 
 	/* alignment */
@@ -386,6 +389,8 @@ struct fdisk_context {
 	struct fdisk_script	*script;	/* what we want to follow */
 };
 
+int fdisk_wipe_collisions(struct fdisk_context *cxt);
+
 /* partition.c */
 int fdisk_partition_next_partno(struct fdisk_partition *pa,
 				       struct fdisk_context *cxt,

libfdisk/src/label.c

@@ -303,6 +303,12 @@ int fdisk_write_disklabel(struct fdisk_context *cxt)
 		return -EINVAL;
 	if (!cxt->label->op->write)
 		return -ENOSYS;
+
+	if (cxt->collision && cxt->wipe_device) {
+		int rc = fdisk_wipe_collisions(cxt);
+		if (rc)
+			return rc;
+	}
 	return cxt->label->op->write(cxt);
 }
 

libfdisk/src/libfdisk.h.in

@@ -190,6 +190,10 @@ int fdisk_is_details(struct fdisk_context *cxt);
 int fdisk_enable_listonly(struct fdisk_context *cxt, int enable);
 int fdisk_is_listonly(struct fdisk_context *cxt);
 
+int fdisk_enable_wipe(struct fdisk_context *cxt, int enable);
+int fdisk_has_wipe(struct fdisk_context *cxt);
+const char *fdisk_get_collision(struct fdisk_context *cxt);
+
 int fdisk_set_unit(struct fdisk_context *cxt, const char *str);
 const char *fdisk_get_unit(struct fdisk_context *cxt, int n);
 int fdisk_use_cylinders(struct fdisk_context *cxt);

libfdisk/src/libfdisk.sym

@@ -253,3 +253,9 @@ FDISK_2.27 {
 	fdisk_get_disklabel_item;
 	fdisk_script_enable_json;
 } FDISK_2.26;
+
+FDISK_2.28 {
+	fdisk_enable_wipe;
+	fdisk_get_collision;
+	fdisk_has_wipe;
+} FDISK_2.27;