diff --git a/common/device-utils.c b/common/device-utils.c
index b67fd45c..c5d1b7e0 100644
--- a/common/device-utils.c
+++ b/common/device-utils.c
@@ -89,7 +89,10 @@ int device_zero_blocks(int fd, off_t start, size_t len)
 
 #define ZERO_DEV_BYTES SZ_2M
 
-/* don't write outside the device by clamping the region to the device size */
+/*
+ * Zero blocks in the range from start but not after the given device size.
+ * (On SPARC the disk labels are preserved too.)
+ */
 static int zero_dev_clamped(int fd, struct btrfs_zoned_device_info *zinfo,
 			    off_t start, ssize_t len, u64 dev_size)
 {
@@ -110,6 +113,9 @@ static int zero_dev_clamped(int fd, struct btrfs_zoned_device_info *zinfo,
 	return device_zero_blocks(fd, start, end - start);
 }
 
+/*
+ * Find all magic signatures known to blkid and remove them
+ */
 static int btrfs_wipe_existing_sb(int fd, struct btrfs_zoned_device_info *zinfo)
 {
 	const char *off = NULL;
@@ -173,6 +179,13 @@ out:
 	return ret;
 }
 
+/*
+ * Prepare a device before it's added to the filesystem. Optionally:
+ * - remove old superblocks
+ * - discard
+ * - reset zones
+ * - delete end of the device
+ */
 int btrfs_prepare_device(int fd, const char *file, u64 *block_count_ret,
 		u64 max_block_count, unsigned opflags)
 {
diff --git a/common/device-utils.h b/common/device-utils.h
index ebd2fb1c..c6b98e5a 100644
--- a/common/device-utils.h
+++ b/common/device-utils.h
@@ -20,18 +20,28 @@
 #include "kerncompat.h"
 #include "sys/stat.h"
 
+/*
+ * Options for btrfs_prepare_device
+ */
 #define	PREP_DEVICE_ZERO_END	(1U << 0)
 #define	PREP_DEVICE_DISCARD	(1U << 1)
 #define	PREP_DEVICE_VERBOSE	(1U << 2)
 #define	PREP_DEVICE_ZONED	(1U << 3)
 
+/*
+ * Generic block device helpers
+ */
 int device_discard_blocks(int fd, u64 start, u64 len);
 int device_zero_blocks(int fd, off_t start, size_t len);
 u64 device_get_partition_size(const char *dev);
 u64 disk_size(const char *path);
+int device_get_queue_param(const char *file, const char *param, char *buf, size_t len);
+
+/*
+ * Updates to devices with btrfs-specific changs
+ */
 u64 btrfs_device_size(int fd, struct stat *st);
 int btrfs_prepare_device(int fd, const char *file, u64 *block_count_ret,
 		u64 max_block_count, unsigned opflags);
-int device_get_queue_param(const char *file, const char *param, char *buf, size_t len);
 
 #endif