diff --git a/img/makefile b/img/makefile
index 38b506a..102e670 100644
--- a/img/makefile
+++ b/img/makefile
@@ -3,7 +3,7 @@ MKFILEPATTERN=../tools/mkfilepattern
 MOUNT_OPT=-t xfs
 TEMP_DIR:=$(shell mktemp -d)
 
-all: s05k s4k unicode v5
+all: s05k s4k unicode v5 kolibri.img
 	rmdir $(TEMP_DIR)
 
 s05k: xfs_v4_ftype0_s05k_b2k_n8k.img xfs_v4_ftype1_s05k_b2k_n8k.img xfs_v4_xattr.img xfs_v4_files_s05k_b4k_n8k.img xfs_v4_ftype0_s05k_b2k_n8k_xattr.img
@@ -14,6 +14,12 @@ unicode: xfs_v4_unicode.img
 
 v5: xfs_v5_ftype1_s05k_b2k_n8k.img xfs_v5_files_s05k_b4k_n8k.img
 
+kolibri.img: ../default.skn
+	touch $@
+	fallocate -z -o 0 -l 1440KiB $@
+	mkfs.vfat -n KOLIBRIOS -F 12 $@
+	mcopy -vmoi $@ $< ::DEFAULT.SKN
+
 xfs_v4_ftype0_s05k_b2k_n8k.img:
 	fallocate -l 63MiB $@
 	sudo mkfs.xfs -b size=2k -m crc=0,finobt=0,rmapbt=0,reflink=0 -d sectsize=512 -i maxpct=100 -n size=8k,ftype=0 $@
@@ -120,15 +126,15 @@ xfs_v4_files_s05k_b4k_n8k.img:
 	sudo mount $(MOUNT_OPT) $@ $(TEMP_DIR)
 	sudo chown $$USER $(TEMP_DIR) -R
 #
-	$(MKFILEPATTERN) $(TEMP_DIR)/no_hole 65536
+	$(MKFILEPATTERN) $(TEMP_DIR)/no_hole 0 65536
 #
-	$(MKFILEPATTERN) $(TEMP_DIR)/hole_begin 65536
+	$(MKFILEPATTERN) $(TEMP_DIR)/hole_begin 0 65536
 	fallocate -p -o 0 -l 16KiB $(TEMP_DIR)/hole_begin
 #
-	$(MKFILEPATTERN) $(TEMP_DIR)/hole_middle 65536
+	$(MKFILEPATTERN) $(TEMP_DIR)/hole_middle 0 65536
 	fallocate -p -o 32KiB -l 16KiB $(TEMP_DIR)/hole_middle
 #
-	$(MKFILEPATTERN) $(TEMP_DIR)/hole_end 65536
+	$(MKFILEPATTERN) $(TEMP_DIR)/hole_end 0 65536
 	fallocate -p -o 48KiB -l 16KiB $(TEMP_DIR)/hole_end
 #
 	fallocate -l 4KiB $(TEMP_DIR)/btree_l1_no_hole
@@ -136,7 +142,12 @@ xfs_v4_files_s05k_b4k_n8k.img:
 		fallocate -i -l 4KiB -o 0KiB $(TEMP_DIR)/btree_l1_no_hole ; \
 		fallocate -z -l 4KiB -o 0KiB $(TEMP_DIR)/btree_l1_no_hole ; \
 	done
-	$(MKFILEPATTERN) $(TEMP_DIR)/btree_l1_no_hole 8196096
+	$(MKFILEPATTERN) $(TEMP_DIR)/btree_l1_no_hole 0 8196096
+#
+#	fallocate -l 5GiB $(TEMP_DIR)/4GiB_plus
+	$(MKFILEPATTERN) $(TEMP_DIR)/4GiB_plus 0x120008000 0x1000
+	$(MKFILEPATTERN) $(TEMP_DIR)/4GiB_plus 0x120000000 0x4000
+	$(MKFILEPATTERN) $(TEMP_DIR)/4GiB_plus 0xffffe000 0x4000
 #
 	sudo umount $(TEMP_DIR)
 	fallocate -i -o 0 -l 1MiB $@ 
@@ -274,15 +285,15 @@ xfs_v5_files_s05k_b4k_n8k.img:
 	sudo mount $(MOUNT_OPT) $@ $(TEMP_DIR)
 	sudo chown $$USER $(TEMP_DIR) -R
 #
-	$(MKFILEPATTERN) $(TEMP_DIR)/no_hole 65536
+	$(MKFILEPATTERN) $(TEMP_DIR)/no_hole 0 65536
 #
-	$(MKFILEPATTERN) $(TEMP_DIR)/hole_begin 65536
+	$(MKFILEPATTERN) $(TEMP_DIR)/hole_begin 0 65536
 	fallocate -p -o 0 -l 16KiB $(TEMP_DIR)/hole_begin
 #
-	$(MKFILEPATTERN) $(TEMP_DIR)/hole_middle 65536
+	$(MKFILEPATTERN) $(TEMP_DIR)/hole_middle 0 65536
 	fallocate -p -o 32KiB -l 16KiB $(TEMP_DIR)/hole_middle
 #
-	$(MKFILEPATTERN) $(TEMP_DIR)/hole_end 65536
+	$(MKFILEPATTERN) $(TEMP_DIR)/hole_end 0 65536
 	fallocate -p -o 48KiB -l 16KiB $(TEMP_DIR)/hole_end
 #
 	fallocate -l 4KiB $(TEMP_DIR)/btree_l1_no_hole
@@ -290,7 +301,7 @@ xfs_v5_files_s05k_b4k_n8k.img:
 		fallocate -i -l 4KiB -o 0KiB $(TEMP_DIR)/btree_l1_no_hole ; \
 		fallocate -z -l 4KiB -o 0KiB $(TEMP_DIR)/btree_l1_no_hole ; \
 	done
-	$(MKFILEPATTERN) $(TEMP_DIR)/btree_l1_no_hole 8196096
+	$(MKFILEPATTERN) $(TEMP_DIR)/btree_l1_no_hole 0 8196096
 #
 	sudo umount $(TEMP_DIR)
 	fallocate -i -o 0 -l 1MiB $@ 
diff --git a/makefile b/makefile
index 59eee80..29ec28c 100644
--- a/makefile
+++ b/makefile
@@ -6,7 +6,7 @@ CFLAGS_32=$(CFLAGS) -m32
 LDFLAGS=
 LDFLAGS_32=$(LDFLAGS) -m32
 
-all: umka_shell umka_fuse umka.sym umka.prp umka.lst tags tools/mkdirrange tools/mkfilepattern covpreproc
+all: umka_shell umka_fuse umka.sym umka.prp umka.lst tags tools/mkdirrange tools/mkfilepattern covpreproc default.skn skin.skn
 
 covpreproc: covpreproc.c
 	$(CC) $(CFLAGS) $(LDFLAGS) $^ -o $@
@@ -17,12 +17,15 @@ umka_shell: umka_shell.o umka.o trace.o trace_lbr.o vdisk.o lodepng.o
 umka_fuse: umka_fuse.o umka.o vdisk.o
 	$(CC) $(LDFLAGS_32) $^ -o $@ `pkg-config fuse3 --libs`
 
-umka.o umka.fas: umka.asm skin.skn
+umka.o umka.fas: umka.asm
 	INCLUDE="$(KOLIBRI)/kernel/trunk;$(KOLIBRI)/programs/develop/libraries/libcrash/trunk" $(FASM) $< umka.o -s umka.fas -m 1234567
 
 lodepng.o: lodepng.c lodepng.h
 	$(CC) $(CFLAGS_32) -c $<
 
+default.skn: $(KOLIBRI)/skins/Leency/Shkvorka/default.asm
+	$(FASM) $< $@
+
 skin.skn: $(KOLIBRI)/skins/Leency/Octo_flat/default.asm
 	$(FASM) $< $@
 
diff --git a/test/makefile b/test/makefile
index 963b491..5beff83 100644
--- a/test/makefile
+++ b/test/makefile
@@ -1,9 +1,9 @@
-ifneq ($(COVERAGE),)
-TASKSET=taskset 1
+ifndef COVERAGE
+UMKA_SHELL=../umka_shell
+else
+UMKA_SHELL=sudo taskset 1 ../umka_shell -c
 endif
 
-UMKA_SHELL=$(TASKSET) ../umka_shell
-
 xfs_tests     := $(addsuffix .out.log, $(basename $(wildcard *\#xfs_*.t)))
 s05k_tests    := $(addsuffix .out.log, $(basename $(wildcard *\#s05k_*.t)))
 s4k_tests     := $(addsuffix .out.log, $(basename $(wildcard *\#s4k_*.t)))
diff --git a/tools/mkfilepattern.c b/tools/mkfilepattern.c
index 24df94e..1c80af6 100644
--- a/tools/mkfilepattern.c
+++ b/tools/mkfilepattern.c
@@ -16,13 +16,15 @@ int main(int argc, char *argv[])
 {
     uint8_t buf[BUF_LEN + 7];
     int64_t len;
+    off_t offset;
     char *path;
-    if (argc != 3) {
-        fprintf(stderr, "mkfilepattern filename size\n");
+    if (argc != 4) {
+        fprintf(stderr, "mkfilepattern filename offset length\n");
         exit(1);
     } else {
         path = argv[1];
-        sscanf(argv[2], "%" SCNi64, &len);
+        offset = strtoll(argv[2], NULL, 0);
+        len = strtoll(argv[3], NULL, 0);
     }
 
     int fd = open(path, O_CREAT | O_WRONLY, S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH);
@@ -31,9 +33,10 @@ int main(int argc, char *argv[])
         exit(1);
     }
 
-    for (int64_t pos = 0, count = BUF_LEN; pos < len; pos += count) {
-        if (count > len - pos) {
-            count = len - pos;
+    lseek(fd, offset, SEEK_SET);
+    for (int64_t pos = offset, count = BUF_LEN; pos < offset + len; pos += count) {
+        if (count > offset + len - pos) {
+            count = offset + len - pos;
         }
 
         off_t off = 0;
diff --git a/trace_lbr.c b/trace_lbr.c
index b9e35be..931331d 100644
--- a/trace_lbr.c
+++ b/trace_lbr.c
@@ -1,4 +1,3 @@
-#define _GNU_SOURCE
 #include <stdint.h>
 #include <unistd.h>
 #include <stdlib.h>
@@ -75,7 +74,6 @@ void set_eflags_tf(uint32_t tf) {
 }
 
 void trace_lbr_begin() {
-    printf("hello from lbr!\n");
     struct sigaction action;
     action.sa_sigaction = &handle_sigtrap;
     action.sa_flags = SA_SIGINFO;
diff --git a/umka_shell.c b/umka_shell.c
index e29fd36..2aa31e7 100644
--- a/umka_shell.c
+++ b/umka_shell.c
@@ -46,14 +46,6 @@
 #define DEFAULT_READDIR_ENCODING UTF8
 #define DEFAULT_PATH_ENCODING UTF8
 
-#define CHECK_OPTION_ARG    \
-    do {                        \
-        if (!argv[++optind]) {  \
-            puts(usage);        \
-            return;             \
-        }                       \
-    } while (0)
-
 diskfunc_t vdisk_functions = {
                                  .strucsize = sizeof(diskfunc_t),
                                  .close = vdisk_close,
@@ -977,10 +969,6 @@ func_table_t funcs[] = {
                         { NULL,                 NULL },
                        };
 
-void usage() {
-    printf("usage: umka_shell [test_file.t]\n");
-}
-
 void *run_test(const char *infile_name) {
     FILE *infile, *outfile;
 
@@ -993,7 +981,6 @@ void *run_test(const char *infile_name) {
         char *last_dot = strrchr(outfile_name, '.');
         if (!last_dot) {
             printf("test file must have '.t' suffix\n");
-            usage();
             return NULL;
         }
         strcpy(last_dot, ".out.log");
@@ -1037,21 +1024,32 @@ void *run_test(const char *infile_name) {
 }
 
 int main(int argc, char **argv) {
+    const char *usage = \
+        "usage: umka_shell [test_file.t] [-c]\n"
+        "  -c               trace branches to collect coverage";
+    const char *test_file = NULL;
+
+    int opt;
+    optind = 1;
+    if (argc > 1 && *argv[optind] != '-') {
+        test_file = argv[optind++];
+    }
+    while ((opt = getopt(argc, argv, "c")) != -1) {
+        switch (opt) {
+        case 'c':
+            trace = 1;
+            break;
+        default:
+            puts(usage);
+            return 1;
+        }
+    }
+
     if (trace)
         trace_begin();
     kos_init();
 
-    switch (argc) {
-    case 1:
-        run_test(NULL);
-        break;
-    case 2: {
-        run_test(argv[1]);
-        break;
-    }
-    default:
-        usage();
-    }
+    run_test(test_file);
 
     if (trace)
         trace_end();