diff --git a/include/pt-mbr.h b/include/pt-mbr.h
index 93a6def6a..81b2aee80 100644
--- a/include/pt-mbr.h
+++ b/include/pt-mbr.h
@@ -19,7 +19,7 @@ struct dos_partition {
 #define MBR_PT_OFFSET		0x1be
 #define MBR_PT_BOOTBITS_SIZE	440
 
-static inline struct dos_partition *mbr_get_partition(unsigned char *mbr, int i)
+static inline struct dos_partition *mbr_get_partition(const unsigned char *mbr, int i)
 {
 	return (struct dos_partition *)
 		(mbr + MBR_PT_OFFSET + (i * sizeof(struct dos_partition)));
@@ -42,7 +42,7 @@ static inline void __dos_store_4le(unsigned char *p, unsigned int val)
 	p[3] = ((val >> 24) & 0xff);
 }
 
-static inline unsigned int dos_partition_get_start(struct dos_partition *p)
+static inline unsigned int dos_partition_get_start(const struct dos_partition *p)
 {
 	return __dos_assemble_4le(&(p->start_sect[0]));
 }
@@ -52,7 +52,7 @@ static inline void dos_partition_set_start(struct dos_partition *p, unsigned int
 	__dos_store_4le(p->start_sect, n);
 }
 
-static inline unsigned int dos_partition_get_size(struct dos_partition *p)
+static inline unsigned int dos_partition_get_size(const struct dos_partition *p)
 {
 	return __dos_assemble_4le(&(p->nr_sects[0]));
 }
diff --git a/libblkid/src/blkidP.h b/libblkid/src/blkidP.h
index 007cc357b..088a8a4c9 100644
--- a/libblkid/src/blkidP.h
+++ b/libblkid/src/blkidP.h
@@ -412,12 +412,12 @@ extern int blkdid_probe_is_opal_locked(blkid_probe pr)
 			__attribute__((nonnull))
 			__attribute__((warn_unused_result));
 
-extern unsigned char *blkid_probe_get_buffer(blkid_probe pr,
+extern const unsigned char *blkid_probe_get_buffer(blkid_probe pr,
                                 uint64_t off, uint64_t len)
 			__attribute__((nonnull))
 			__attribute__((warn_unused_result));
 
-extern unsigned char *blkid_probe_get_sector(blkid_probe pr, unsigned int sector)
+extern const unsigned char *blkid_probe_get_sector(blkid_probe pr, unsigned int sector)
 			__attribute__((nonnull))
 			__attribute__((warn_unused_result));
 
@@ -434,7 +434,7 @@ extern int blkid_probe_get_idmag(blkid_probe pr, const struct blkid_idinfo *id,
 			__attribute__((nonnull(1)));
 
 /* returns superblock according to 'struct blkid_idmag' */
-extern unsigned char *blkid_probe_get_sb_buffer(blkid_probe pr, const struct blkid_idmag *mag, size_t size);
+extern const unsigned char *blkid_probe_get_sb_buffer(blkid_probe pr, const struct blkid_idmag *mag, size_t size);
 #define blkid_probe_get_sb(_pr, _mag, type) \
 			((type *) blkid_probe_get_sb_buffer((_pr), _mag, sizeof(type)))
 
diff --git a/libblkid/src/partitions/bsd.c b/libblkid/src/partitions/bsd.c
index ba120195e..20dab6b3e 100644
--- a/libblkid/src/partitions/bsd.c
+++ b/libblkid/src/partitions/bsd.c
@@ -47,7 +47,7 @@ static int probe_bsd_pt(blkid_probe pr, const struct blkid_idmag *mag)
 	blkid_partition parent;
 	blkid_partlist ls;
 	int i, nparts = BSD_MAXPARTITIONS;
-	unsigned char *data;
+	const unsigned char *data;
 	int rc = BLKID_PROBE_NONE;
 	uint32_t abs_offset = 0;
 
diff --git a/libblkid/src/partitions/dos.c b/libblkid/src/partitions/dos.c
index 5c7718c3e..d5a8aa3ae 100644
--- a/libblkid/src/partitions/dos.c
+++ b/libblkid/src/partitions/dos.c
@@ -34,7 +34,7 @@ static const struct dos_subtypes {
 	{ MBR_MINIX_PARTITION, &minix_pt_idinfo }
 };
 
-static inline int is_extended(struct dos_partition *p)
+static inline int is_extended(const struct dos_partition *p)
 {
 	return (p->sys_ind == MBR_DOS_EXTENDED_PARTITION ||
 		p->sys_ind == MBR_W95_EXTENDED_PARTITION ||
@@ -46,7 +46,7 @@ static int parse_dos_extended(blkid_probe pr, blkid_parttable tab,
 {
 	blkid_partlist ls = blkid_probe_get_partlist(pr);
 	uint32_t cur_start = ex_start, cur_size = ex_size;
-	unsigned char *data;
+	const unsigned char *data;
 	int ct_nodata = 0;	/* count ext.partitions without data partitions */
 	int i;
 
@@ -57,7 +57,7 @@ static int parse_dos_extended(blkid_probe pr, blkid_parttable tab,
 	}
 
 	while (1) {
-		struct dos_partition *p, *p0;
+		const struct dos_partition *p, *p0;
 		uint32_t start = 0, size;
 
 		if (++ct_nodata > 100)
@@ -156,9 +156,9 @@ static inline int is_lvm(blkid_probe pr)
 	return (v && v->data && strcmp((char *) v->data, "LVM2_member") == 0);
 }
 
-static inline int is_empty_mbr(unsigned char *mbr)
+static inline int is_empty_mbr(const unsigned char *mbr)
 {
-	struct dos_partition *p = mbr_get_partition(mbr, 0);
+	const struct dos_partition *p = mbr_get_partition(mbr, 0);
 	int i, nparts = 0;
 
 	for (i = 0; i < 4; i++) {
@@ -177,8 +177,8 @@ static int probe_dos_pt(blkid_probe pr,
 	int ssf;
 	blkid_parttable tab = NULL;
 	blkid_partlist ls;
-	struct dos_partition *p0, *p;
-	unsigned char *data;
+	const struct dos_partition *p0, *p;
+	const unsigned char *data;
 	uint32_t start, size, id;
 	char idstr[UUID_STR_LEN];
 
diff --git a/libblkid/src/partitions/gpt.c b/libblkid/src/partitions/gpt.c
index 89e7bb679..473bf5c0e 100644
--- a/libblkid/src/partitions/gpt.c
+++ b/libblkid/src/partitions/gpt.c
@@ -109,7 +109,7 @@ static inline uint32_t count_crc32(const unsigned char *buf, size_t len,
 	return (ul_crc32_exclude_offset(~0L, buf, len, exclude_off, exclude_len) ^ ~0L);
 }
 
-static inline unsigned char *get_lba_buffer(blkid_probe pr,
+static inline const unsigned char *get_lba_buffer(blkid_probe pr,
 					uint64_t lba, size_t bytes)
 {
 	return blkid_probe_get_buffer(pr,
@@ -161,8 +161,8 @@ static int last_lba(blkid_probe pr, uint64_t *lba)
 static int is_pmbr_valid(blkid_probe pr, int *has)
 {
 	int flags = blkid_partitions_get_flags(pr);
-	unsigned char *data;
-	struct dos_partition *p;
+	const unsigned char *data;
+	const struct dos_partition *p;
 	int i;
 
 	if (has)
diff --git a/libblkid/src/partitions/mac.c b/libblkid/src/partitions/mac.c
index 75a558b0a..36ce74ed3 100644
--- a/libblkid/src/partitions/mac.c
+++ b/libblkid/src/partitions/mac.c
@@ -56,7 +56,7 @@ struct mac_driver_desc {
 	/* there is more stuff after this that we don't need */
 } __attribute__((packed));
 
-static inline unsigned char *get_mac_block(
+static inline const unsigned char *get_mac_block(
 					blkid_probe pr,
 					uint16_t block_size,
 					uint32_t num)
diff --git a/libblkid/src/partitions/minix.c b/libblkid/src/partitions/minix.c
index 43c9d9af1..dee7df95b 100644
--- a/libblkid/src/partitions/minix.c
+++ b/libblkid/src/partitions/minix.c
@@ -17,11 +17,11 @@
 static int probe_minix_pt(blkid_probe pr,
 		const struct blkid_idmag *mag __attribute__((__unused__)))
 {
-	struct dos_partition *p;
+	const struct dos_partition *p;
 	blkid_parttable tab = NULL;
 	blkid_partition parent;
 	blkid_partlist ls;
-	unsigned char *data;
+	const unsigned char *data;
 	int i;
 
 	data = blkid_probe_get_sector(pr, 0);
diff --git a/libblkid/src/partitions/ultrix.c b/libblkid/src/partitions/ultrix.c
index 9c060be1d..a85712fad 100644
--- a/libblkid/src/partitions/ultrix.c
+++ b/libblkid/src/partitions/ultrix.c
@@ -37,8 +37,8 @@ struct ultrix_disklabel {
 static int probe_ultrix_pt(blkid_probe pr,
 		const struct blkid_idmag *mag __attribute__((__unused__)))
 {
-	unsigned char *data;
-	struct ultrix_disklabel *l;
+	const unsigned char *data;
+	const struct ultrix_disklabel *l;
 	blkid_parttable tab = NULL;
 	blkid_partlist ls;
 	int i;
@@ -50,7 +50,7 @@ static int probe_ultrix_pt(blkid_probe pr,
 		goto nothing;
 	}
 
-	l = (struct ultrix_disklabel *) (data + ULTRIX_OFFSET);
+	l = (const struct ultrix_disklabel *) (data + ULTRIX_OFFSET);
 
 	if (l->pt_magic != ULTRIX_MAGIC || l->pt_valid != 1)
 		goto nothing;
diff --git a/libblkid/src/probe.c b/libblkid/src/probe.c
index b4299493f..fdad0c266 100644
--- a/libblkid/src/probe.c
+++ b/libblkid/src/probe.c
@@ -669,7 +669,7 @@ static int hide_buffer(blkid_probe pr, uint64_t off, uint64_t len)
  * Note that @off is offset within probing area, the probing area is defined by
  * pr->off and pr->size.
  */
-unsigned char *blkid_probe_get_buffer(blkid_probe pr, uint64_t off, uint64_t len)
+const unsigned char *blkid_probe_get_buffer(blkid_probe pr, uint64_t off, uint64_t len)
 {
 	struct blkid_bufinfo *bf = NULL;
 	uint64_t real_off = pr->off + off;
@@ -1136,7 +1136,7 @@ int blkid_probe_set_dimension(blkid_probe pr, uint64_t off, uint64_t size)
 	return 0;
 }
 
-unsigned char *blkid_probe_get_sb_buffer(blkid_probe pr, const struct blkid_idmag *mag, size_t size)
+const unsigned char *blkid_probe_get_sb_buffer(blkid_probe pr, const struct blkid_idmag *mag, size_t size)
 {
 	uint64_t hint_offset;
 
@@ -1164,7 +1164,7 @@ int blkid_probe_get_idmag(blkid_probe pr, const struct blkid_idinfo *id,
 
 	/* try to detect by magic string */
 	while(mag && mag->magic) {
-		unsigned char *buf;
+		const unsigned char *buf;
 		uint64_t kboff;
 		uint64_t hint_offset;
 
@@ -1690,7 +1690,7 @@ done:
 }
 
 /* same sa blkid_probe_get_buffer() but works with 512-sectors */
-unsigned char *blkid_probe_get_sector(blkid_probe pr, unsigned int sector)
+const unsigned char *blkid_probe_get_sector(blkid_probe pr, unsigned int sector)
 {
 	return blkid_probe_get_buffer(pr, ((uint64_t) sector) << 9, 0x200);
 }
diff --git a/libblkid/src/superblocks/bcache.c b/libblkid/src/superblocks/bcache.c
index 7e8d78db5..c8ac52425 100644
--- a/libblkid/src/superblocks/bcache.c
+++ b/libblkid/src/superblocks/bcache.c
@@ -118,7 +118,7 @@ struct bcachefs_super_block {
 static int bcache_verify_checksum(blkid_probe pr, const struct blkid_idmag *mag,
 		const struct bcache_super_block *bcs)
 {
-	unsigned char *csummed = blkid_probe_get_sb_buffer(pr, mag, BCACHE_SB_CSUMMED_END);
+	const unsigned char *csummed = blkid_probe_get_sb_buffer(pr, mag, BCACHE_SB_CSUMMED_END);
 	uint64_t csum = ul_crc64_we(csummed + BCACHE_SB_CSUMMED_START,
 			BCACHE_SB_CSUMMED_END - BCACHE_SB_CSUMMED_START);
 	return blkid_probe_verify_csum(pr, csum, le64_to_cpu(bcs->csum));
@@ -168,7 +168,7 @@ static void probe_bcachefs_sb_members(blkid_probe pr,
 	blkid_probe_set_fssize(pr, sectors * BCACHEFS_SECTOR_SIZE);
 }
 
-static int is_within_range(void *start, uint64_t size, void *end)
+static int is_within_range(const void *start, uint64_t size, const void *end)
 {
 	ptrdiff_t diff;
 
@@ -180,9 +180,9 @@ static int is_within_range(void *start, uint64_t size, void *end)
 }
 
 static void probe_bcachefs_sb_fields(blkid_probe pr, const struct bcachefs_super_block *bcs,
-				     unsigned char *sb_start, unsigned char *sb_end)
+				     const unsigned char *sb_start, const unsigned char *sb_end)
 {
-	unsigned char *field_addr = sb_start + BCACHEFS_SB_FIELDS_OFF;
+	const unsigned char *field_addr = sb_start + BCACHEFS_SB_FIELDS_OFF;
 
 	while (1) {
 		struct bcachefs_sb_field *field = (struct bcachefs_sb_field *) field_addr;
@@ -212,10 +212,10 @@ static void probe_bcachefs_sb_fields(blkid_probe pr, const struct bcachefs_super
 }
 
 static int bcachefs_validate_checksum(blkid_probe pr, const struct bcachefs_super_block *bcs,
-				      unsigned char *sb, unsigned char *sb_end)
+				      const unsigned char *sb, const unsigned char *sb_end)
 {
 	uint8_t checksum_type = be64_to_cpu(bcs->flags[0]) >> 58;
-	unsigned char *checksummed_data_start = sb + sizeof(bcs->csum);
+	const unsigned char *checksummed_data_start = sb + sizeof(bcs->csum);
 	size_t checksummed_data_size = sb_end - checksummed_data_start;
 
 	switch (checksum_type) {
@@ -242,7 +242,7 @@ static int bcachefs_validate_checksum(blkid_probe pr, const struct bcachefs_supe
 static int probe_bcachefs(blkid_probe pr, const struct blkid_idmag *mag)
 {
 	struct bcachefs_super_block *bcs;
-	unsigned char *sb, *sb_end;
+	const unsigned char *sb, *sb_end;
 	uint64_t sb_size, blocksize;
 
 	bcs = blkid_probe_get_sb(pr, mag, struct bcachefs_super_block);
diff --git a/libblkid/src/superblocks/befs.c b/libblkid/src/superblocks/befs.c
index 5112d44f4..d501eb105 100644
--- a/libblkid/src/superblocks/befs.c
+++ b/libblkid/src/superblocks/befs.c
@@ -122,7 +122,7 @@ struct bplustree_node {
 	char		name[0];
 } __attribute__((packed));
 
-static unsigned char *get_block_run(blkid_probe pr, const struct befs_super_block *bs,
+static const unsigned char *get_block_run(blkid_probe pr, const struct befs_super_block *bs,
 					const struct block_run *br, int fs_le)
 {
 	return blkid_probe_get_buffer(pr,
@@ -135,7 +135,7 @@ static unsigned char *get_block_run(blkid_probe pr, const struct befs_super_bloc
 					<< FS32_TO_CPU(bs->block_shift, fs_le));
 }
 
-static unsigned char *get_custom_block_run(blkid_probe pr,
+static const unsigned char *get_custom_block_run(blkid_probe pr,
 				const struct befs_super_block *bs,
 				const struct block_run *br,
 				int64_t offset, uint32_t length, int fs_le)
@@ -154,7 +154,7 @@ static unsigned char *get_custom_block_run(blkid_probe pr,
 			length);
 }
 
-static unsigned char *get_tree_node(blkid_probe pr, const struct befs_super_block *bs,
+static const unsigned char *get_tree_node(blkid_probe pr, const struct befs_super_block *bs,
 				const struct data_stream *ds,
 				int64_t start, uint32_t length, int fs_le)
 {
diff --git a/libblkid/src/superblocks/cramfs.c b/libblkid/src/superblocks/cramfs.c
index 2a87acdaa..81aa377c4 100644
--- a/libblkid/src/superblocks/cramfs.c
+++ b/libblkid/src/superblocks/cramfs.c
@@ -55,7 +55,7 @@ static int cramfs_verify_csum(blkid_probe pr, const struct blkid_idmag *mag,
 		struct cramfs_super *cs, int le)
 {
 	uint32_t crc, expected, csummed_size;
-	unsigned char *csummed;
+	const unsigned char *csummed;
 
 	expected = cfs32_to_cpu(le, cs->info.crc);
 	csummed_size = cfs32_to_cpu(le, cs->size);
@@ -67,9 +67,10 @@ static int cramfs_verify_csum(blkid_probe pr, const struct blkid_idmag *mag,
 	csummed = blkid_probe_get_sb_buffer(pr, mag, csummed_size);
 	if (!csummed)
 		return 0;
-	memset(csummed + offsetof(struct cramfs_super, info.crc), 0, sizeof(uint32_t));
 
-	crc = ~ul_crc32(~0LL, csummed, csummed_size);
+	crc = ~ul_crc32_exclude_offset(~0LL, csummed, csummed_size,
+			offsetof(struct cramfs_super, info.crc),
+			sizeof_member(struct cramfs_super, info.crc));
 
 	return blkid_probe_verify_csum(pr, crc, expected);
 }
diff --git a/libblkid/src/superblocks/ddf_raid.c b/libblkid/src/superblocks/ddf_raid.c
index 0b82e73eb..66b49396a 100644
--- a/libblkid/src/superblocks/ddf_raid.c
+++ b/libblkid/src/superblocks/ddf_raid.c
@@ -106,7 +106,7 @@ static int probe_ddf(blkid_probe pr,
 
 	if (lba > 0) {
 		/* check primary header */
-		unsigned char *buf;
+		const unsigned char *buf;
 
 		buf = blkid_probe_get_buffer(pr,
 					lba << 9, sizeof(ddf->signature));
diff --git a/libblkid/src/superblocks/erofs.c b/libblkid/src/superblocks/erofs.c
index 14d272efe..672cd7fdc 100644
--- a/libblkid/src/superblocks/erofs.c
+++ b/libblkid/src/superblocks/erofs.c
@@ -46,7 +46,7 @@ static int erofs_verify_checksum(blkid_probe pr, const struct blkid_idmag *mag,
 {
 	uint32_t expected, csum;
 	size_t csummed_size;
-	unsigned char *csummed;
+	const unsigned char *csummed;
 
 	if (!(le32_to_cpu(sb->feature_compat) & EROFS_FEATURE_SB_CSUM))
 		return 1;
diff --git a/libblkid/src/superblocks/exfat.c b/libblkid/src/superblocks/exfat.c
index 370340487..554868f4f 100644
--- a/libblkid/src/superblocks/exfat.c
+++ b/libblkid/src/superblocks/exfat.c
@@ -119,7 +119,7 @@ static struct exfat_entry_label *find_label(blkid_probe pr,
 }
 
 /* From https://docs.microsoft.com/en-us/windows/win32/fileio/exfat-specification#34-main-and-backup-boot-checksum-sub-regions */
-static uint32_t exfat_boot_checksum(unsigned char *sectors,
+static uint32_t exfat_boot_checksum(const unsigned char *sectors,
 				    size_t sector_size)
 {
 	uint32_t n_bytes = sector_size * 11;
@@ -141,7 +141,7 @@ static int exfat_validate_checksum(blkid_probe pr,
 {
 	size_t sector_size = BLOCK_SIZE(sb);
 	/* 11 sectors will be checksummed, the 12th contains the expected */
-	unsigned char *data = blkid_probe_get_buffer(pr, 0, sector_size * 12);
+	const unsigned char *data = blkid_probe_get_buffer(pr, 0, sector_size * 12);
 	if (!data)
 		return 0;
 
diff --git a/libblkid/src/superblocks/f2fs.c b/libblkid/src/superblocks/f2fs.c
index 980111ef3..5ee3442fc 100644
--- a/libblkid/src/superblocks/f2fs.c
+++ b/libblkid/src/superblocks/f2fs.c
@@ -67,14 +67,14 @@ static int f2fs_validate_checksum(blkid_probe pr, size_t sb_off,
 	if (csum_off + sizeof(uint32_t) > 4096)
 		return 0;
 
-	unsigned char *csum_data = blkid_probe_get_buffer(pr,
+	const unsigned char *csum_data = blkid_probe_get_buffer(pr,
 			sb_off + csum_off, sizeof(uint32_t));
 	if (!csum_data)
 		return 0;
 
 	uint32_t expected = le32_to_cpu(*(uint32_t *) csum_data);
 
-	unsigned char *csummed = blkid_probe_get_buffer(pr, sb_off, csum_off);
+	const unsigned char *csummed = blkid_probe_get_buffer(pr, sb_off, csum_off);
 	if (!csummed)
 		return 0;
 
diff --git a/libblkid/src/superblocks/hfs.c b/libblkid/src/superblocks/hfs.c
index 68cb30edb..184c98e0d 100644
--- a/libblkid/src/superblocks/hfs.c
+++ b/libblkid/src/superblocks/hfs.c
@@ -183,11 +183,11 @@ static int probe_hfs(blkid_probe pr, const struct blkid_idmag *mag)
 static int probe_hfsplus(blkid_probe pr, const struct blkid_idmag *mag)
 {
 	struct hfsplus_extent extents[HFSPLUS_EXTENT_COUNT];
-	struct hfsplus_bnode_descriptor *descr;
-	struct hfsplus_bheader_record *bnode;
-	struct hfsplus_catalog_key *key;
-	struct hfsplus_vol_header *hfsplus;
-	struct hfs_mdb *sbd;
+	const struct hfsplus_bnode_descriptor *descr;
+	const struct hfsplus_bheader_record *bnode;
+	const struct hfsplus_catalog_key *key;
+	const struct hfsplus_vol_header *hfsplus;
+	const struct hfs_mdb *sbd;
 	unsigned int alloc_block_size;
 	unsigned int alloc_first_block;
 	unsigned int embed_first_block;
@@ -203,7 +203,7 @@ static int probe_hfsplus(blkid_probe pr, const struct blkid_idmag *mag)
 	unsigned int leaf_block;
 	int ext;
 	uint64_t leaf_off;
-	unsigned char *buf;
+	const unsigned char *buf;
 
 	sbd = blkid_probe_get_sb(pr, mag, struct hfs_mdb);
 	if (!sbd)
@@ -225,7 +225,7 @@ static int probe_hfsplus(blkid_probe pr, const struct blkid_idmag *mag)
 		buf = blkid_probe_get_buffer(pr,
 				off + (mag->kboff * 1024),
 				sizeof(struct hfsplus_vol_header));
-		hfsplus = (struct hfsplus_vol_header *) buf;
+		hfsplus = (const struct hfsplus_vol_header *) buf;
 
 	} else
 		hfsplus = blkid_probe_get_sb(pr, mag,
diff --git a/libblkid/src/superblocks/iso9660.c b/libblkid/src/superblocks/iso9660.c
index 536704b4e..dbed1628c 100644
--- a/libblkid/src/superblocks/iso9660.c
+++ b/libblkid/src/superblocks/iso9660.c
@@ -232,7 +232,7 @@ static int probe_iso9660(blkid_probe pr, const struct blkid_idmag *mag)
 		return probe_iso9660_hsfs(pr, mag);
 
 	for (i = 0, off += ISO_SUPERBLOCK_OFFSET; i < ISO_VD_MAX && (!boot || !pvd || !joliet); i++, off += ISO_SECTOR_SIZE) {
-		unsigned char *desc =
+		const unsigned char *desc =
 			blkid_probe_get_buffer(pr,
 					off,
 					max(sizeof(struct boot_record),
diff --git a/libblkid/src/superblocks/linux_raid.c b/libblkid/src/superblocks/linux_raid.c
index 360cd4eb3..156b0bf48 100644
--- a/libblkid/src/superblocks/linux_raid.c
+++ b/libblkid/src/superblocks/linux_raid.c
@@ -187,15 +187,14 @@ static int raid1_verify_csum(blkid_probe pr, off_t off,
 {
 	size_t csummed_size = sizeof(struct mdp1_super_block)
 		+ le32_to_cpu(mdp1->max_dev) * sizeof(mdp1->dev_roles[0]);
-	unsigned char *csummed = blkid_probe_get_buffer(pr, off, csummed_size);
+	const unsigned char *csummed = blkid_probe_get_buffer(pr, off, csummed_size);
 	if (!csummed)
 		return 1;
 
-	memset(csummed + offsetof(struct mdp1_super_block, sb_csum), 0,
-			sizeof(mdp1->sb_csum));
-
 	uint64_t csum = 0;
 
+	csum -= le32_to_cpu(*(uint32_t *) (csummed + offsetof(struct mdp1_super_block, sb_csum)));
+
 	while (csummed_size >= 4) {
 		csum += le32_to_cpu(*(uint32_t *) csummed);
 		csummed_size -= 4;
diff --git a/libblkid/src/superblocks/lvm.c b/libblkid/src/superblocks/lvm.c
index eea74d657..71ca13202 100644
--- a/libblkid/src/superblocks/lvm.c
+++ b/libblkid/src/superblocks/lvm.c
@@ -76,7 +76,7 @@ static int probe_lvm2(blkid_probe pr, const struct blkid_idmag *mag)
 	int sector = mag->kboff << 1;
 	struct lvm2_pv_label_header *label;
 	char uuid[LVM2_ID_LEN + 7];
-	unsigned char *buf;
+	const unsigned char *buf;
 
 	buf = blkid_probe_get_buffer(pr,
 			mag->kboff << 10,
diff --git a/libblkid/src/superblocks/minix.c b/libblkid/src/superblocks/minix.c
index c68ade9c9..dba299d23 100644
--- a/libblkid/src/superblocks/minix.c
+++ b/libblkid/src/superblocks/minix.c
@@ -74,7 +74,7 @@ static int get_minix_version(const unsigned char *data, int *other_endian)
 static int probe_minix(blkid_probe pr,
 		const struct blkid_idmag *mag __attribute__((__unused__)))
 {
-	unsigned char *ext;
+	const unsigned char *ext;
 	const unsigned char *data;
 	int version = 0, swabme = 0;
 	unsigned long zones, ninodes, imaps, zmaps;
diff --git a/libblkid/src/superblocks/ntfs.c b/libblkid/src/superblocks/ntfs.c
index 8309ea8ca..d0dbb60fa 100644
--- a/libblkid/src/superblocks/ntfs.c
+++ b/libblkid/src/superblocks/ntfs.c
@@ -80,13 +80,13 @@ struct file_attribute {
 
 static int __probe_ntfs(blkid_probe pr, const struct blkid_idmag *mag, int save_info)
 {
-	struct ntfs_super_block *ns;
-	struct master_file_table_record *mft;
+	const struct ntfs_super_block *ns;
+	const struct master_file_table_record *mft;
 
 	uint32_t sectors_per_cluster, mft_record_size;
 	uint16_t sector_size;
 	uint64_t nr_clusters, off, attr_off;
-	unsigned char *buf_mft;
+	const unsigned char *buf_mft;
 
 	ns = blkid_probe_get_sb(pr, mag, struct ntfs_super_block);
 	if (!ns)
diff --git a/libblkid/src/superblocks/ocfs.c b/libblkid/src/superblocks/ocfs.c
index e213d66b4..14f74d391 100644
--- a/libblkid/src/superblocks/ocfs.c
+++ b/libblkid/src/superblocks/ocfs.c
@@ -100,7 +100,7 @@ struct oracle_asm_disk_label {
 
 static int probe_ocfs(blkid_probe pr, const struct blkid_idmag *mag)
 {
-	unsigned char *buf;
+	const unsigned char *buf;
 	struct ocfs_volume_header ovh;
 	struct ocfs_volume_label ovl;
 	uint32_t maj, min;
diff --git a/libblkid/src/superblocks/romfs.c b/libblkid/src/superblocks/romfs.c
index 456cbfb7d..805e8fc1e 100644
--- a/libblkid/src/superblocks/romfs.c
+++ b/libblkid/src/superblocks/romfs.c
@@ -29,7 +29,7 @@ static int romfs_verify_csum(blkid_probe pr, const struct blkid_idmag *mag,
 {
 	uint32_t csummed_size = min((uint32_t) 512,
 			be32_to_cpu(ros->ros_full_size));
-	unsigned char *csummed;
+	const unsigned char *csummed;
 	uint32_t csum;
 
 	if (csummed_size % sizeof(uint32_t) != 0)
diff --git a/libblkid/src/superblocks/stratis.c b/libblkid/src/superblocks/stratis.c
index fe4a45277..4cd94c087 100644
--- a/libblkid/src/superblocks/stratis.c
+++ b/libblkid/src/superblocks/stratis.c
@@ -49,7 +49,7 @@ const char STRATIS_MAGIC[] = "!Stra0tis\x86\xff\x02^\x41rh";
 #define MAGIC_OFFSET_COPY_1 (FIRST_COPY_OFFSET + _MAGIC_OFFSET)
 #define MAGIC_OFFSET_COPY_2 (SECOND_COPY_OFFSET + _MAGIC_OFFSET)
 
-static int stratis_valid_sb(uint8_t *p)
+static int stratis_valid_sb(const uint8_t *p)
 {
 	const struct stratis_sb *stratis = (const struct stratis_sb *)p;
 	uint32_t crc = 0;
@@ -83,7 +83,7 @@ static int probe_stratis(blkid_probe pr,
 		const struct blkid_idmag *mag __attribute__((__unused__)))
 {
 	const struct stratis_sb *stratis = NULL;
-	uint8_t *buf = blkid_probe_get_buffer(pr, 0, SB_AREA_SIZE);
+	const uint8_t *buf = blkid_probe_get_buffer(pr, 0, SB_AREA_SIZE);
 	unsigned char uuid[STRATIS_UUID_STR_LEN];
 
 	if (!buf)
diff --git a/libblkid/src/superblocks/swap.c b/libblkid/src/superblocks/swap.c
index 67224bc63..c7fbec308 100644
--- a/libblkid/src/superblocks/swap.c
+++ b/libblkid/src/superblocks/swap.c
@@ -91,7 +91,7 @@ static int swap_set_info(blkid_probe pr, const struct blkid_idmag *mag,
 
 static int probe_swap(blkid_probe pr, const struct blkid_idmag *mag)
 {
-	unsigned char *buf;
+	const unsigned char *buf;
 
 	if (!mag)
 		return 1;
diff --git a/libblkid/src/superblocks/vfat.c b/libblkid/src/superblocks/vfat.c
index 6d3b09171..dacf5afd5 100644
--- a/libblkid/src/superblocks/vfat.c
+++ b/libblkid/src/superblocks/vfat.c
@@ -351,7 +351,7 @@ static int probe_vfat(blkid_probe pr, const struct blkid_idmag *mag)
 			version = "FAT16";
 
 	} else if (vs->vs_fat32_length) {
-		unsigned char *buf;
+		const unsigned char *buf;
 		uint16_t fsinfo_sect;
 		int maxloop = 100;
 
diff --git a/libblkid/src/superblocks/vmfs.c b/libblkid/src/superblocks/vmfs.c
index fac87abe5..ff96136c8 100644
--- a/libblkid/src/superblocks/vmfs.c
+++ b/libblkid/src/superblocks/vmfs.c
@@ -49,7 +49,7 @@ static int probe_vmfs_fs(blkid_probe pr, const struct blkid_idmag *mag)
 static int probe_vmfs_volume(blkid_probe pr, const struct blkid_idmag *mag)
 {
 	struct vmfs_volume_info *header;
-	unsigned char *lvm_uuid;
+	const unsigned char *lvm_uuid;
 
 	header = blkid_probe_get_sb(pr, mag, struct vmfs_volume_info);
 	if (header == NULL)
diff --git a/libblkid/src/superblocks/xfs.c b/libblkid/src/superblocks/xfs.c
index f0e099e57..a592469fd 100644
--- a/libblkid/src/superblocks/xfs.c
+++ b/libblkid/src/superblocks/xfs.c
@@ -206,7 +206,7 @@ static int xfs_verify_sb(struct xfs_super_block *ondisk, blkid_probe pr,
 
 	if ((sbp->sb_versionnum & 0x0f) == 5) {
 		uint32_t expected, crc;
-		unsigned char *csummed;
+		const unsigned char *csummed;
 
 		if (!(sbp->sb_versionnum & XFS_SB_VERSION_MOREBITSBIT))
 			return 0;
@@ -331,7 +331,7 @@ static int probe_xfs_log(blkid_probe pr,
 {
 	int i;
 	struct xlog_rec_header *rhead;
-	unsigned char *buf;
+	const unsigned char *buf;
 
 	buf = blkid_probe_get_buffer(pr, 0, 256*1024);
 	if (!buf)
diff --git a/libblkid/src/superblocks/zfs.c b/libblkid/src/superblocks/zfs.c
index 1fcc38409..008a20082 100644
--- a/libblkid/src/superblocks/zfs.c
+++ b/libblkid/src/superblocks/zfs.c
@@ -71,13 +71,13 @@ struct nvlist {
 	struct nvpair	nvl_nvpair;
 };
 
-static void zfs_process_value(blkid_probe pr, char *name, size_t namelen,
-			     void *value, size_t max_value_size, unsigned directory_level)
+static void zfs_process_value(blkid_probe pr, const char *name, size_t namelen,
+			     const void *value, size_t max_value_size, unsigned directory_level)
 {
 	if (strncmp(name, "name", namelen) == 0 &&
 	    sizeof(struct nvstring) <= max_value_size &&
 	    !directory_level) {
-		struct nvstring *nvs = value;
+		const struct nvstring *nvs = value;
 		uint32_t nvs_type = be32_to_cpu(nvs->nvs_type);
 		uint32_t nvs_strlen = be32_to_cpu(nvs->nvs_strlen);
 
@@ -92,7 +92,7 @@ static void zfs_process_value(blkid_probe pr, char *name, size_t namelen,
 	} else if (strncmp(name, "guid", namelen) == 0 &&
 		   sizeof(struct nvuint64) <= max_value_size &&
 		   !directory_level) {
-		struct nvuint64 *nvu = value;
+		const struct nvuint64 *nvu = value;
 		uint32_t nvu_type = be32_to_cpu(nvu->nvu_type);
 		uint64_t nvu_value;
 
@@ -110,7 +110,7 @@ static void zfs_process_value(blkid_probe pr, char *name, size_t namelen,
 	} else if (strncmp(name, "pool_guid", namelen) == 0 &&
 		   sizeof(struct nvuint64) <= max_value_size &&
 		   !directory_level) {
-		struct nvuint64 *nvu = value;
+		const struct nvuint64 *nvu = value;
 		uint32_t nvu_type = be32_to_cpu(nvu->nvu_type);
 		uint64_t nvu_value;
 
@@ -128,7 +128,7 @@ static void zfs_process_value(blkid_probe pr, char *name, size_t namelen,
 					 "%"PRIu64, nvu_value);
 	} else if (strncmp(name, "ashift", namelen) == 0 &&
 		   sizeof(struct nvuint64) <= max_value_size) {
-		struct nvuint64 *nvu = value;
+		const struct nvuint64 *nvu = value;
 		uint32_t nvu_type = be32_to_cpu(nvu->nvu_type);
 		uint64_t nvu_value;
 
@@ -147,9 +147,9 @@ static void zfs_process_value(blkid_probe pr, char *name, size_t namelen,
 
 static void zfs_extract_guid_name(blkid_probe pr, loff_t offset)
 {
-	unsigned char *p;
-	struct nvlist *nvl;
-	struct nvpair *nvp;
+	const unsigned char *p;
+	const struct nvlist *nvl;
+	const struct nvpair *nvp;
 	size_t left = 4096;
 	unsigned directory_level = 0;
 
@@ -166,16 +166,16 @@ static void zfs_extract_guid_name(blkid_probe pr, loff_t offset)
 	DBG(LOWPROBE, ul_debug("zfs_extract: nvlist offset %jd",
 			       (intmax_t)offset));
 
-	nvl = (struct nvlist *) p;
+	nvl = (const struct nvlist *) p;
 	nvp = &nvl->nvl_nvpair;
-	left -= (unsigned char *)nvp - p; /* Already used up 12 bytes */
+	left -= (const unsigned char *)nvp - p; /* Already used up 12 bytes */
 
 	while (left > sizeof(*nvp)) {
 		uint32_t nvp_size = be32_to_cpu(nvp->nvp_size);
 		uint32_t nvp_namelen = be32_to_cpu(nvp->nvp_namelen);
 		uint64_t namesize = ((uint64_t)nvp_namelen + 3) & ~3;
 		size_t max_value_size;
-		void *value;
+		const void *value;
 
 		if (!nvp->nvp_size) {
 			if (!directory_level)
@@ -201,7 +201,7 @@ static void zfs_extract_guid_name(blkid_probe pr, loff_t offset)
 		value = nvp->nvp_name + namesize;
 
 		if (sizeof(struct nvdirectory) <= max_value_size) {
-			struct nvdirectory *nvu = value;
+			const struct nvdirectory *nvu = value;
 			if (be32_to_cpu(nvu->nvd_type) == DATA_TYPE_DIRECTORY) {
 				nvp_size = sizeof(*nvp) + namesize + sizeof(*nvu);
 				directory_level++;
@@ -259,7 +259,7 @@ static int probe_zfs(blkid_probe pr,
 	struct zfs_uberblock *ub = NULL;
 	loff_t offset = 0, ub_offset = 0;
 	int label_no, found = 0, found_in_label;
-	void *label;
+	const void *label;
 	loff_t blk_align = (pr->size % (256 * 1024ULL));
 
 	DBG(PROBE, ul_debug("probe_zfs"));
diff --git a/libfdisk/src/dos.c b/libfdisk/src/dos.c
index 7970ae139..1d17943b8 100644
--- a/libfdisk/src/dos.c
+++ b/libfdisk/src/dos.c
@@ -792,7 +792,7 @@ static void get_partition_table_geometry(struct fdisk_context *cxt,
 	unsigned char *bufp = cxt->firstsector;
 	struct { unsigned int c, h, o, v; } t[8];
 	unsigned int n1, n2, n3, n4, n5, n6;
-	struct dos_partition *p;
+	const struct dos_partition *p;
 	unsigned int c, h, s, l;
 	unsigned int hh, ss;
 	unsigned int sects;