libblkid: ignore private LVM devices

The virtual private LVM devices do not contain any blkid relevant data
and it does not make any sense to scan for superblocks or partitions
on the devices, because we can interpret data from the devices in bad
way.

Unfortunately, for LVM has "private" very special meaning. The private
LVM devices are accessible and readable (according to LVM guys it's
feature, because debugging etc.).

The problem is pretty visible with LVM thin provisioning where a virtual
pool device contains segments from the top-level thin devices.

Mountable top-level LVM-thin device:

	# blkid -o udev -p /dev/mapper/vg-thin1
	ID_FS_UUID=57ed6490-903b-416c-91d2-6d06804ec60c
	ID_FS_TYPE=ext4

Virtual private LVM-pool device (contains data from all thin devices):

	# blkid -o udev -p /dev/mapper/vg-pool0
	ID_FS_UUID=57ed6490-903b-416c-91d2-6d06804ec60c
	ID_FS_TYPE=ext4

... this is incorrect, vg-pool0 is unmountable.

LVM uses special UUID suffixes for private devices. All devices with
uuid in format "LVM-<uuid>-<type>" are private.

This patch modifies libblkid to not scan such devices. The high-level
API ignores such devices at all now.

The low-level API allows to assign the device to blkid_prober, but all
scan functions always return nothing and library does not read
anything from the device. The another functionality (get parental
device, topology, sector sizes, etc.) still works as expected. The
change affects only probing code.

Addresses: https://bugzilla.redhat.com/show_bug.cgi?id=1101345
Signed-off-by: Karel Zak <kzak@redhat.com>

libblkid/src/blkidP.h

@@ -219,6 +219,7 @@ struct blkid_struct_probe
 #define BLKID_FL_PRIVATE_FD	(1 << 1)	/* see blkid_new_probe_from_filename() */
 #define BLKID_FL_TINY_DEV	(1 << 2)	/* <= 1.47MiB (floppy or so) */
 #define BLKID_FL_CDROM_DEV	(1 << 3)	/* is a CD/DVD drive */
+#define BLKID_FL_NOSCAN_DEV	(1 << 4)	/* do not scan this device */
 
 /* private per-probing flags */
 #define BLKID_PROBE_FL_IGNORE_PT (1 << 1)	/* ignore partition table */
@@ -347,6 +348,7 @@ extern void blkid__scan_dir(char *, dev_t, struct dir_list **, char **)
 			__attribute__((nonnull(1,4)));
 extern int blkid_driver_has_major(const char *drvname, int major)
 			__attribute__((warn_unused_result));
+extern int blkid_lvm_private(dev_t devno);
 
 /* lseek.c */
 extern blkid_loff_t blkid_llseek(int fd, blkid_loff_t offset, int whence);

libblkid/src/devno.c

@@ -326,6 +326,34 @@ int blkid_driver_has_major(const char *drvname, int major)
 	return match;
 }
 
+/*
+ * Returns 1 if the device is private LVM device.
+ */
+int blkid_lvm_private(dev_t devno)
+{
+	struct sysfs_cxt cxt = UL_SYSFSCXT_EMPTY;
+	char *uuid = NULL;
+	int rc = 0;
+
+	if (sysfs_init(&cxt, devno, NULL) != 0)
+		return 0;
+
+	uuid = sysfs_strdup(&cxt, "dm/uuid");
+
+	/* Private LVM devices use "LVM-<uuid>-<name>" uuid format (important
+	 * is the "LVM" prefix and "-<name>" postfix).
+	 */
+	if (uuid && strncmp(uuid, "LVM-", 4) == 0) {
+		char *p = strrchr(uuid + 4, '-');
+
+		if (p && *(p + 1))
+			rc = 1;
+	}
+
+	sysfs_deinit(&cxt);
+	free(uuid);
+	return rc;
+}
 
 #ifdef TEST_PROGRAM
 int main(int argc, char** argv)

libblkid/src/partitions/partitions.c

@@ -540,6 +540,8 @@ static int idinfo_probe(blkid_probe pr, const struct blkid_idinfo *id,
 
 	if (pr->size <= 0 || (id->minsz && id->minsz > pr->size))
 		goto nothing;	/* the device is too small */
+	if (pr->flags & BLKID_FL_NOSCAN_DEV)
+		goto nothing;
 
 	rc = blkid_probe_get_idmag(pr, id, &off, &mag);
 	if (rc != BLKID_PROBE_OK)
@@ -579,6 +581,9 @@ static int partitions_probe(blkid_probe pr, struct blkid_chain *chn)
 
 	if (!pr || chn->idx < -1)
 		return -EINVAL;
+	if (pr->flags & BLKID_FL_NOSCAN_DEV)
+		goto done;			/* nothing */
+
 	blkid_probe_chain_reset_vals(pr, chn);
 
 	if (chn->binary)
@@ -648,7 +653,7 @@ details_only:
 			rc = xrc;
 	}
 
-
+done:
 	DBG(LOWPROBE, ul_debug("partitions probe done [rc=%d]",	rc));
 	return rc;
 }
@@ -668,6 +673,8 @@ int blkid_partitions_do_subprobe(blkid_probe pr, blkid_partition parent,
 
 	if (!pr || !parent || !parent->size)
 		return -EINVAL;
+	if (pr->flags & BLKID_FL_NOSCAN_DEV)
+		return BLKID_PROBE_NONE;
 
 	/* range defined by parent */
 	sz = ((blkid_loff_t) parent->size) << 9;
@@ -724,6 +731,9 @@ static int blkid_partitions_probe_partition(blkid_probe pr)
 
 	DBG(LOWPROBE, ul_debug("parts: start probing for partition entry"));
 
+	if (pr->flags & BLKID_FL_NOSCAN_DEV)
+		goto nothing;
+
 	devno = blkid_probe_get_devno(pr);
 	if (!devno)
 		goto nothing;
@@ -797,7 +807,7 @@ nothing:
 int blkid_probe_is_covered_by_pt(blkid_probe pr,
 				 blkid_loff_t offset, blkid_loff_t size)
 {
-	blkid_probe prc;
+	blkid_probe prc = NULL;
 	blkid_partlist ls = NULL;
 	blkid_loff_t start, end;
 	int nparts, i, rc = 0;
@@ -806,6 +816,9 @@ int blkid_probe_is_covered_by_pt(blkid_probe pr,
 		"=> checking if off=%jd size=%jd covered by PT",
 		offset, size));
 
+	if (pr->flags & BLKID_FL_NOSCAN_DEV)
+		goto done;
+
 	prc = blkid_clone_probe(pr);
 	if (!prc)
 		goto done;

libblkid/src/probe.c

@@ -696,6 +696,7 @@ int blkid_probe_set_device(blkid_probe pr, int fd,
 	if (!S_ISBLK(sb.st_mode) && !S_ISCHR(sb.st_mode) && !S_ISREG(sb.st_mode))
 		goto err;
 
+
 	pr->mode = sb.st_mode;
 	if (S_ISBLK(sb.st_mode) || S_ISCHR(sb.st_mode))
 		pr->devno = sb.st_rdev;
@@ -724,8 +725,13 @@ int blkid_probe_set_device(blkid_probe pr, int fd,
 	if (pr->size <= 1440 * 1024 && !S_ISCHR(sb.st_mode))
 		pr->flags |= BLKID_FL_TINY_DEV;
 
+	if (S_ISBLK(sb.st_mode) && blkid_lvm_private(sb.st_rdev)) {
+		DBG(LOWPROBE, ul_debug("ignore private LVM device"));
+		pr->flags |= BLKID_FL_NOSCAN_DEV;
+	}
+
 #ifdef CDROM_GET_CAPABILITY
-	if (S_ISBLK(sb.st_mode) &&
+	else if (S_ISBLK(sb.st_mode) &&
 	    !blkid_probe_is_tiny(pr) &&
 	    blkid_probe_is_wholedisk(pr) &&
 	    ioctl(fd, CDROM_GET_CAPABILITY, NULL) >= 0)
@@ -896,6 +902,9 @@ int blkid_do_probe(blkid_probe pr)
 	if (!pr)
 		return -1;
 
+	if (pr->flags & BLKID_FL_NOSCAN_DEV)
+		return 1;
+
 	do {
 		struct blkid_chain *chn = pr->cur_chain;
 
@@ -1147,6 +1156,8 @@ int blkid_do_safeprobe(blkid_probe pr)
 
 	if (!pr)
 		return -1;
+	if (pr->flags & BLKID_FL_NOSCAN_DEV)
+		return 1;
 
 	blkid_probe_start(pr);
 
@@ -1201,6 +1212,8 @@ int blkid_do_fullprobe(blkid_probe pr)
 
 	if (!pr)
 		return -1;
+	if (pr->flags & BLKID_FL_NOSCAN_DEV)
+		return 1;
 
 	blkid_probe_start(pr);
 

libblkid/src/superblocks/superblocks.c

@@ -340,6 +340,9 @@ static int superblocks_probe(blkid_probe pr, struct blkid_chain *chn)
 
 	if (!pr || chn->idx < -1)
 		return -EINVAL;
+	if (pr->flags & BLKID_FL_NOSCAN_DEV)
+		goto nothing;
+
 	blkid_probe_chain_reset_vals(pr, chn);
 
 	DBG(LOWPROBE, ul_debug("--> starting probing loop [SUBLKS idx=%d]",
@@ -455,6 +458,9 @@ static int superblocks_safeprobe(blkid_probe pr, struct blkid_chain *chn)
 	int intol = 0;
 	int rc;
 
+	if (pr->flags & BLKID_FL_NOSCAN_DEV)
+		return 1;				/* nothing */
+
 	while ((rc = superblocks_probe(pr, chn)) == 0) {
 
 		if (blkid_probe_is_tiny(pr) && !count)

libblkid/src/verify.c

@@ -112,6 +112,10 @@ blkid_dev blkid_verify(blkid_cache cache, blkid_dev dev)
 		   (unsigned long)diff));
 #endif
 
+	if (blkid_lvm_private(st.st_rdev)) {
+		blkid_free_dev(dev);
+		return NULL;
+	}
 	if (!cache->probe) {
 		cache->probe = blkid_new_probe();
 		if (!cache->probe) {