diff --git a/utils/src/ioctl.h b/utils/src/ioctl.h
index 447b4f8e..b8e8aa40 100644
--- a/utils/src/ioctl.h
+++ b/utils/src/ioctl.h
@@ -122,8 +122,30 @@ struct scoutfs_ioctl_ino_path {
 
 #define SCOUTFS_IOC_DATA_VERSION _IOW(SCOUTFS_IOCTL_MAGIC, 4, __u64)
 
+/*
+ * "Release" a contiguous range of logical blocks of file data.
+ * Released blocks are removed from the file system like truncation, but
+ * an offline record is left behind to trigger demand staging if the
+ * file is read.
+ *
+ * The starting block offset and number of blocks to release are in
+ * units 4KB blocks.
+ *
+ * The specified range can extend past i_size and can straddle sparse
+ * regions or blocks that are already offline.  The only change it makes
+ * is to free and mark offline any existing blocks that intersect with
+ * the region.
+ *
+ * Returns 0 if the operation succeeds.  If an error is returned then
+ * some partial region of the blocks in the region may have been marked
+ * offline.
+ *
+ * If the operation succeeds then inode metadata that reflects file data
+ * contents are not updated.  This is intended to be transparent to the
+ * presentation of the data in the file.
+ */
 struct scoutfs_ioctl_release {
-	__u64 offset;
+	__u64 block;
 	__u64 count;
 	__u64 data_version;
 } __packed;
diff --git a/utils/src/stage_release.c b/utils/src/stage_release.c
index 61750b1a..1efbaa7d 100644
--- a/utils/src/stage_release.c
+++ b/utils/src/stage_release.c
@@ -127,7 +127,7 @@ static int release_cmd(int argc, char **argv)
 {
 	struct scoutfs_ioctl_release args;
 	char *endptr = NULL;
-	u64 offset;
+	u64 block;
 	u64 count;
 	u64 vers;
 	int ret;
@@ -155,10 +155,10 @@ static int release_cmd(int argc, char **argv)
 		goto out;
 	}
 
-	offset = strtoull(argv[2], &endptr, 0);
+	block = strtoull(argv[2], &endptr, 0);
 	if (*endptr != '\0' ||
-	    ((offset == LLONG_MIN || offset == LLONG_MAX) && errno == ERANGE)) {
-		fprintf(stderr, "error parsing starting offset '%s'\n",
+	    ((block == LLONG_MIN || block == LLONG_MAX) && errno == ERANGE)) {
+		fprintf(stderr, "error parsing starting 4K block offset '%s'\n",
 			argv[2]);
 		ret = -EINVAL;
 		goto out;
@@ -173,7 +173,7 @@ static int release_cmd(int argc, char **argv)
 		goto out;
 	}
 
-	args.offset = offset;
+	args.block = block;
 	args.count = count;
 	args.data_version = vers;
 
@@ -190,6 +190,6 @@ out:
 
 static void __attribute__((constructor)) release_ctor(void)
 {
-	cmd_register("release", "<path> <vers> <offset> <count>",
+	cmd_register("release", "<path> <vers> <4K block offset> <block count>",
 		     "mark file region offline and free extents", release_cmd);
 }