make grade 100/100

61810

.gitignore

@@ -15,3 +15,12 @@ mkfs
 kernel/kernel
 user/usys.S
 .gdbinit
+myapi.key
+*-handin.tar.gz
+xv6.out*
+.vagrant/
+submissions/
+ph
+barrier
+/lab-*.json
+.DS_Store

Makefile

@@ -1,14 +1,16 @@
+
+# To compile and run with a lab solution, set the lab name in conf/lab.mk
+# (e.g., LAB=util).  Run make grade to test solution with the lab's
+# grade script (e.g., grade-lab-util).
+
+-include conf/lab.mk
+
 K=kernel
 U=user
 
 OBJS = \
   $K/entry.o \
-  $K/start.o \
-  $K/console.o \
-  $K/printf.o \
-  $K/uart.o \
   $K/kalloc.o \
-  $K/spinlock.o \
   $K/string.o \
   $K/main.o \
   $K/vm.o \
@@ -30,6 +32,34 @@ OBJS = \
   $K/plic.o \
   $K/virtio_disk.o
 
+OBJS_KCSAN = \
+  $K/start.o \
+  $K/console.o \
+  $K/printf.o \
+  $K/uart.o \
+  $K/spinlock.o
+
+ifdef KCSAN
+OBJS_KCSAN += \
+	$K/kcsan.o
+endif
+
+ifeq ($(LAB),$(filter $(LAB), lock))
+OBJS += \
+	$K/stats.o\
+	$K/sprintf.o
+endif
+
+
+ifeq ($(LAB),net)
+OBJS += \
+	$K/e1000.o \
+	$K/net.o \
+	$K/sysnet.o \
+	$K/pci.o
+endif
+
+
 # riscv64-unknown-elf- or riscv64-linux-gnu-
 # perhaps in /opt/riscv/bin
 #TOOLPREFIX = 
@@ -57,12 +87,28 @@ OBJCOPY = $(TOOLPREFIX)objcopy
 OBJDUMP = $(TOOLPREFIX)objdump
 
 CFLAGS = -Wall -Werror -O -fno-omit-frame-pointer -ggdb -gdwarf-2
+
+ifdef LAB
+LABUPPER = $(shell echo $(LAB) | tr a-z A-Z)
+XCFLAGS += -DSOL_$(LABUPPER) -DLAB_$(LABUPPER)
+endif
+
+CFLAGS += $(XCFLAGS)
 CFLAGS += -MD
 CFLAGS += -mcmodel=medany
 CFLAGS += -ffreestanding -fno-common -nostdlib -mno-relax
 CFLAGS += -I.
 CFLAGS += $(shell $(CC) -fno-stack-protector -E -x c /dev/null >/dev/null 2>&1 && echo -fno-stack-protector)
 
+ifeq ($(LAB),net)
+CFLAGS += -DNET_TESTS_PORT=$(SERVERPORT)
+endif
+
+ifdef KCSAN
+CFLAGS += -DKCSAN
+KCSANFLAG = -fsanitize=thread -fno-inline
+endif
+
 # Disable PIE when possible (for Ubuntu 16.10 toolchain)
 ifneq ($(shell $(CC) -dumpspecs 2>/dev/null | grep -e '[^f]no-pie'),)
 CFLAGS += -fno-pie -no-pie
@@ -73,11 +119,17 @@ endif
 
 LDFLAGS = -z max-page-size=4096
 
-$K/kernel: $(OBJS) $K/kernel.ld $U/initcode
+$K/kernel: $(OBJS) $(OBJS_KCSAN) $K/kernel.ld $U/initcode
-	$(LD) $(LDFLAGS) -T $K/kernel.ld -o $K/kernel $(OBJS) 
+	$(LD) $(LDFLAGS) -T $K/kernel.ld -o $K/kernel $(OBJS) $(OBJS_KCSAN)
 	$(OBJDUMP) -S $K/kernel > $K/kernel.asm
 	$(OBJDUMP) -t $K/kernel | sed '1,/SYMBOL TABLE/d; s/ .* / /; /^$$/d' > $K/kernel.sym
 
+$(OBJS): EXTRAFLAG := $(KCSANFLAG)
+
+$K/%.o: $K/%.c
+	$(CC) $(CFLAGS) $(EXTRAFLAG) -c -o $@ $<
+
+
 $U/initcode: $U/initcode.S
 	$(CC) $(CFLAGS) -march=rv64g -nostdinc -I. -Ikernel -c $U/initcode.S -o $U/initcode.o
 	$(LD) $(LDFLAGS) -N -e start -Ttext 0 -o $U/initcode.out $U/initcode.o
@@ -89,6 +141,10 @@ tags: $(OBJS) _init
 
 ULIB = $U/ulib.o $U/usys.o $U/printf.o $U/umalloc.o
 
+ifeq ($(LAB),$(filter $(LAB), lock))
+ULIB += $U/statistics.o
+endif
+
 _%: %.o $(ULIB)
 	$(LD) $(LDFLAGS) -T $U/user.ld -o $@ $^
 	$(OBJDUMP) -S $@ > $*.asm
@@ -107,7 +163,7 @@ $U/_forktest: $U/forktest.o $(ULIB)
 	$(OBJDUMP) -S $U/_forktest > $U/forktest.asm
 
 mkfs/mkfs: mkfs/mkfs.c $K/fs.h $K/param.h
-	gcc -Werror -Wall -I. -o mkfs/mkfs mkfs/mkfs.c
+	gcc $(XCFLAGS) -Werror -Wall -I. -o mkfs/mkfs mkfs/mkfs.c
 
 # Prevent deletion of intermediate files, e.g. cat.o, after first build, so
 # that disk image changes after first build are persistent until clean.  More
@@ -132,9 +188,81 @@ UPROGS=\
 	$U/_grind\
 	$U/_wc\
 	$U/_zombie\
+	$U/_symlinktest\
 
-fs.img: mkfs/mkfs README $(UPROGS)
+
-	mkfs/mkfs fs.img README $(UPROGS)
+
+
+ifeq ($(LAB),$(filter $(LAB), lock))
+UPROGS += \
+	$U/_stats
+endif
+
+ifeq ($(LAB),traps)
+UPROGS += \
+	$U/_call\
+	$U/_bttest
+endif
+
+ifeq ($(LAB),lazy)
+UPROGS += \
+	$U/_lazytests
+endif
+
+ifeq ($(LAB),cow)
+UPROGS += \
+	$U/_cowtest
+endif
+
+ifeq ($(LAB),thread)
+UPROGS += \
+	$U/_uthread
+
+$U/uthread_switch.o : $U/uthread_switch.S
+	$(CC) $(CFLAGS) -c -o $U/uthread_switch.o $U/uthread_switch.S
+
+$U/_uthread: $U/uthread.o $U/uthread_switch.o $(ULIB)
+	$(LD) $(LDFLAGS) -N -e main -Ttext 0 -o $U/_uthread $U/uthread.o $U/uthread_switch.o $(ULIB)
+	$(OBJDUMP) -S $U/_uthread > $U/uthread.asm
+
+ph: notxv6/ph.c
+	gcc -o ph -g -O2 $(XCFLAGS) notxv6/ph.c -pthread
+
+barrier: notxv6/barrier.c
+	gcc -o barrier -g -O2 $(XCFLAGS) notxv6/barrier.c -pthread
+endif
+
+ifeq ($(LAB),pgtbl)
+UPROGS += \
+	$U/_pgtbltest
+endif
+
+ifeq ($(LAB),lock)
+UPROGS += \
+	$U/_kalloctest\
+	$U/_bcachetest
+endif
+
+ifeq ($(LAB),fs)
+UPROGS += \
+	$U/_bigfile
+endif
+
+
+
+ifeq ($(LAB),net)
+UPROGS += \
+	$U/_nettests
+endif
+
+UEXTRA=
+ifeq ($(LAB),util)
+	UEXTRA += user/xargstest.sh
+endif
+
+
+fs.img: mkfs/mkfs README $(UEXTRA) $(UPROGS)
+	mkfs/mkfs fs.img README $(UEXTRA) $(UPROGS)
 
 -include kernel/*.d user/*.d
 
@@ -144,7 +272,8 @@ clean:
 	$U/initcode $U/initcode.out $K/kernel fs.img \
 	mkfs/mkfs .gdbinit \
         $U/usys.S \
-	$(UPROGS)
+	$(UPROGS) \
+	ph barrier
 
 # try to generate a unique GDB port
 GDBPORT = $(shell expr `id -u` % 5000 + 25000)
@@ -155,12 +284,22 @@ QEMUGDB = $(shell if $(QEMU) -help | grep -q '^-gdb'; \
 ifndef CPUS
 CPUS := 3
 endif
+ifeq ($(LAB),fs)
+CPUS := 1
+endif
+
+FWDPORT = $(shell expr `id -u` % 5000 + 25999)
 
 QEMUOPTS = -machine virt -bios none -kernel $K/kernel -m 128M -smp $(CPUS) -nographic
 QEMUOPTS += -global virtio-mmio.force-legacy=false
 QEMUOPTS += -drive file=fs.img,if=none,format=raw,id=x0
 QEMUOPTS += -device virtio-blk-device,drive=x0,bus=virtio-mmio-bus.0
 
+ifeq ($(LAB),net)
+QEMUOPTS += -netdev user,id=net0,hostfwd=udp::$(FWDPORT)-:2000 -object filter-dump,id=net0,netdev=net0,file=packets.pcap
+QEMUOPTS += -device e1000,netdev=net0,bus=pcie.0
+endif
+
 qemu: $K/kernel fs.img
 	$(QEMU) $(QEMUOPTS)
 
@@ -171,3 +310,102 @@ qemu-gdb: $K/kernel .gdbinit fs.img
 	@echo "*** Now run 'gdb' in another window." 1>&2
 	$(QEMU) $(QEMUOPTS) -S $(QEMUGDB)
 
+ifeq ($(LAB),net)
+# try to generate a unique port for the echo server
+SERVERPORT = $(shell expr `id -u` % 5000 + 25099)
+
+server:
+	python3 server.py $(SERVERPORT)
+
+ping:
+	python3 ping.py $(FWDPORT)
+endif
+
+##
+##  FOR testing lab grading script
+##
+
+ifneq ($(V),@)
+GRADEFLAGS += -v
+endif
+
+print-gdbport:
+	@echo $(GDBPORT)
+
+grade:
+	@echo $(MAKE) clean
+	@$(MAKE) clean || \
+          (echo "'make clean' failed.  HINT: Do you have another running instance of xv6?" && exit 1)
+	./grade-lab-$(LAB) $(GRADEFLAGS)
+
+##
+## FOR web handin
+##
+
+
+WEBSUB := https://6828.scripts.mit.edu/2022/handin.py
+
+handin: tarball-pref myapi.key
+	@SUF=$(LAB); \
+	curl -f -F file=@lab-$$SUF-handin.tar.gz -F key=\<myapi.key $(WEBSUB)/upload \
+	    > /dev/null || { \
+		echo ; \
+		echo Submit seems to have failed.; \
+		echo Please go to $(WEBSUB)/ and upload the tarball manually.; }
+
+handin-check:
+	@if ! test -d .git; then \
+		echo No .git directory, is this a git repository?; \
+		false; \
+	fi
+	@if test "$$(git symbolic-ref HEAD)" != refs/heads/$(LAB); then \
+		git branch; \
+		read -p "You are not on the $(LAB) branch.  Hand-in the current branch? [y/N] " r; \
+		test "$$r" = y; \
+	fi
+	@if ! git diff-files --quiet || ! git diff-index --quiet --cached HEAD; then \
+		git status -s; \
+		echo; \
+		echo "You have uncomitted changes.  Please commit or stash them."; \
+		false; \
+	fi
+	@if test -n "`git status -s`"; then \
+		git status -s; \
+		read -p "Untracked files will not be handed in.  Continue? [y/N] " r; \
+		test "$$r" = y; \
+	fi
+
+UPSTREAM := $(shell git remote -v | grep -m 1 "xv6-labs-2022" | awk '{split($$0,a," "); print a[1]}')
+
+tarball: handin-check
+	git archive --format=tar HEAD | gzip > lab-$(LAB)-handin.tar.gz
+
+tarball-pref: handin-check
+	@SUF=$(LAB); \
+	git archive --format=tar HEAD > lab-$$SUF-handin.tar; \
+	git diff $(UPSTREAM)/$(LAB) > /tmp/lab-$$SUF-diff.patch; \
+	tar -rf lab-$$SUF-handin.tar /tmp/lab-$$SUF-diff.patch; \
+	gzip -c lab-$$SUF-handin.tar > lab-$$SUF-handin.tar.gz; \
+	rm lab-$$SUF-handin.tar; \
+	rm /tmp/lab-$$SUF-diff.patch; \
+
+myapi.key:
+	@echo Get an API key for yourself by visiting $(WEBSUB)/
+	@read -p "Please enter your API key: " k; \
+	if test `echo "$$k" |tr -d '\n' |wc -c` = 32 ; then \
+		TF=`mktemp -t tmp.XXXXXX`; \
+		if test "x$$TF" != "x" ; then \
+			echo "$$k" |tr -d '\n' > $$TF; \
+			mv -f $$TF $@; \
+		else \
+			echo mktemp failed; \
+			false; \
+		fi; \
+	else \
+		echo Bad API key: $$k; \
+		echo An API key should be 32 characters long.; \
+		false; \
+	fi;
+
+
+.PHONY: handin tarball tarball-pref clean grade handin-check

README

@@ -6,7 +6,7 @@ ACKNOWLEDGMENTS
 
 xv6 is inspired by John Lions's Commentary on UNIX 6th Edition (Peer
 to Peer Communications; ISBN: 1-57398-013-7; 1st edition (June 14,
-2000)).  See also https://pdos.csail.mit.edu/6.828/, which provides
+2000)).  See also https://pdos.csail.mit.edu/6.1810/, which provides
 pointers to on-line resources for v6.
 
 The following people have made contributions: Russ Cox (context switching,
@@ -14,29 +14,31 @@ locking), Cliff Frey (MP), Xiao Yu (MP), Nickolai Zeldovich, and Austin
 Clements.
 
 We are also grateful for the bug reports and patches contributed by
-Takahiro Aoyagi, Silas Boyd-Wickizer, Anton Burtsev, Ian Chen, Dan
+Takahiro Aoyagi, Silas Boyd-Wickizer, Anton Burtsev, carlclone, Ian
-Cross, Cody Cutler, Mike CAT, Tej Chajed, Asami Doi, eyalz800, Nelson
+Chen, Dan Cross, Cody Cutler, Mike CAT, Tej Chajed, Asami Doi,
-Elhage, Saar Ettinger, Alice Ferrazzi, Nathaniel Filardo, flespark,
+eyalz800, Nelson Elhage, Saar Ettinger, Alice Ferrazzi, Nathaniel
-Peter Froehlich, Yakir Goaron, Shivam Handa, Matt Harvey, Bryan Henry,
+Filardo, flespark, Peter Froehlich, Yakir Goaron, Shivam Handa, Matt
-jaichenhengjie, Jim Huang, Matúš Jókay, Alexander Kapshuk, Anders
+Harvey, Bryan Henry, jaichenhengjie, Jim Huang, Matúš Jókay, John
-Kaseorg, kehao95, Wolfgang Keller, Jungwoo Kim, Jonathan Kimmitt,
+Jolly, Alexander Kapshuk, Anders Kaseorg, kehao95, Wolfgang Keller,
-Eddie Kohler, Vadim Kolontsov, Austin Liew, l0stman, Pavan
+Jungwoo Kim, Jonathan Kimmitt, Eddie Kohler, Vadim Kolontsov, Austin
-Maddamsetti, Imbar Marinescu, Yandong Mao, Matan Shabtay, Hitoshi
+Liew, l0stman, Pavan Maddamsetti, Imbar Marinescu, Yandong Mao, Matan
-Mitake, Carmi Merimovich, Mark Morrissey, mtasm, Joel Nider,
+Shabtay, Hitoshi Mitake, Carmi Merimovich, Mark Morrissey, mtasm, Joel
-OptimisticSide, Greg Price, Jude Rich, Ayan Shafqat, Eldar Sehayek,
+Nider, Hayato Ohhashi, OptimisticSide, Harry Porter, Greg Price, Jude
-Yongming Shen, Fumiya Shigemitsu, Cam Tenny, tyfkda, Warren Toomey,
+Rich, segfault, Ayan Shafqat, Eldar Sehayek, Yongming Shen, Fumiya
-Stephen Tu, Rafael Ubal, Amane Uehara, Pablo Ventura, Xi Wang, Keiichi
+Shigemitsu, Cam Tenny, tyfkda, Warren Toomey, Stephen Tu, Rafael Ubal,
-Watanabe, Nicolas Wolovick, wxdao, Grant Wu, Jindong Zhang, Icenowy
+Amane Uehara, Pablo Ventura, Xi Wang, WaheedHafez, Keiichi Watanabe,
-Zheng, ZhUyU1997, and Zou Chang Wei.
+Nicolas Wolovick, wxdao, Grant Wu, Jindong Zhang, Icenowy Zheng,
+ZhUyU1997, and Zou Chang Wei.
+
 
 The code in the files that constitute xv6 is
-Copyright 2006-2020 Frans Kaashoek, Robert Morris, and Russ Cox.
+Copyright 2006-2022 Frans Kaashoek, Robert Morris, and Russ Cox.
 
 ERROR REPORTS
 
 Please send errors and suggestions to Frans Kaashoek and Robert Morris
 (kaashoek,rtm@mit.edu).  The main purpose of xv6 is as a teaching
-operating system for MIT's 6.S081, so we are more interested in
+operating system for MIT's 6.1810, so we are more interested in
 simplifications and clarifications than new features.
 
 BUILDING AND RUNNING XV6

conf/lab.mk

@@ -0,0 +1 @@
+LAB=fs

grade-lab-fs

@@ -0,0 +1,41 @@
+#!/usr/bin/env python3
+
+import re
+from gradelib import *
+
+r = Runner(save("xv6.out"))
+
+@test(40, "running bigfile")
+def test_bigfile():
+    r.run_qemu(shell_script([
+        'bigfile'
+    ]), timeout=400)
+    r.match('^wrote 65803 blocks$')
+    r.match('^bigfile done; ok$')
+
+@test(0, "running symlinktest")
+def test_symlinktest():
+    r.run_qemu(shell_script([
+        'symlinktest'
+    ]), timeout=20)
+
+@test(20, "symlinktest: symlinks", parent=test_symlinktest)
+def test_symlinktest_symlinks():
+    r.match("^test symlinks: ok$")
+
+@test(20, "symlinktest: concurrent symlinks", parent=test_symlinktest)
+def test_symlinktest_symlinks():
+    r.match("^test concurrent symlinks: ok$")
+
+@test(19, "usertests")
+def test_usertests():
+    r.run_qemu(shell_script([
+        'usertests -q'
+    ]), timeout=600)
+    r.match('^ALL TESTS PASSED$')
+
+@test(1, "time")
+def test_time():
+    check_time()
+
+run_tests()

gradelib.py

@@ -0,0 +1,611 @@
+from __future__ import print_function
+
+import sys, os, re, time, socket, select, subprocess, errno, shutil, random, string
+from subprocess import check_call, Popen
+from optparse import OptionParser
+
+__all__ = []
+
+##################################################################
+# Test structure
+#
+
+__all__ += ["test", "end_part", "run_tests", "get_current_test"]
+
+TESTS = []
+TOTAL = POSSIBLE = 0
+PART_TOTAL = PART_POSSIBLE = 0
+CURRENT_TEST = None
+
+def test(points, title=None, parent=None):
+    """Decorator for declaring test functions.  If title is None, the
+    title of the test will be derived from the function name by
+    stripping the leading "test_" and replacing underscores with
+    spaces."""
+
+    def register_test(fn, title=title):
+        if not title:
+            assert fn.__name__.startswith("test_")
+            title = fn.__name__[5:].replace("_", " ")
+        if parent:
+            title = "  " + title
+
+        def run_test():
+            global TOTAL, POSSIBLE, CURRENT_TEST
+
+            # Handle test dependencies
+            if run_test.complete:
+                return run_test.ok
+            run_test.complete = True
+            parent_failed = False
+            if parent:
+                parent_failed = not parent()
+
+            # Run the test
+            fail = None
+            start = time.time()
+            CURRENT_TEST = run_test
+            sys.stdout.write("== Test %s == " % title)
+            if parent:
+                sys.stdout.write("\n")
+            sys.stdout.flush()
+            try:
+                if parent_failed:
+                    raise AssertionError('Parent failed: %s' % parent.__name__)
+                fn()
+            except AssertionError as e:
+                fail = str(e)
+
+            # Display and handle test result
+            POSSIBLE += points
+            if points:
+                print("%s: %s" % (title, \
+                    (color("red", "FAIL") if fail else color("green", "OK"))), end=' ')
+            if time.time() - start > 0.1:
+                print("(%.1fs)" % (time.time() - start), end=' ')
+            print()
+            if fail:
+                print("    %s" % fail.replace("\n", "\n    "))
+            else:
+                TOTAL += points
+            for callback in run_test.on_finish:
+                callback(fail)
+            CURRENT_TEST = None
+
+            run_test.ok = not fail
+            return run_test.ok
+
+        # Record test metadata on the test wrapper function
+        run_test.__name__ = fn.__name__
+        run_test.title = title
+        run_test.complete = False
+        run_test.ok = False
+        run_test.on_finish = []
+        TESTS.append(run_test)
+        return run_test
+    return register_test
+
+def end_part(name):
+    def show_part():
+        global PART_TOTAL, PART_POSSIBLE
+        print("Part %s score: %d/%d" % \
+            (name, TOTAL - PART_TOTAL, POSSIBLE - PART_POSSIBLE))
+        print()
+        PART_TOTAL, PART_POSSIBLE = TOTAL, POSSIBLE
+    show_part.title = ""
+    TESTS.append(show_part)
+
+def run_tests():
+    """Set up for testing and run the registered test functions."""
+
+    # Handle command line
+    global options
+    parser = OptionParser(usage="usage: %prog [-v] [filters...]")
+    parser.add_option("-v", "--verbose", action="store_true",
+                      help="print commands")
+    parser.add_option("--color", choices=["never", "always", "auto"],
+                      default="auto", help="never, always, or auto")
+    (options, args) = parser.parse_args()
+
+    # Start with a full build to catch build errors
+    make()
+
+    # Clean the file system if there is one
+    reset_fs()
+
+    # Run tests
+    limit = list(map(str.lower, args))
+    try:
+        for test in TESTS:
+            if not limit or any(l in test.title.lower() for l in limit):
+                test()
+        if not limit:
+            print("Score: %d/%d" % (TOTAL, POSSIBLE))
+    except KeyboardInterrupt:
+        pass
+    if TOTAL < POSSIBLE:
+        sys.exit(1)
+
+def get_current_test():
+    if not CURRENT_TEST:
+        raise RuntimeError("No test is running")
+    return CURRENT_TEST
+
+##################################################################
+# Assertions
+#
+
+__all__ += ["assert_equal", "assert_lines_match"]
+
+def assert_equal(got, expect, msg=""):
+    if got == expect:
+        return
+    if msg:
+        msg += "\n"
+    raise AssertionError("%sgot:\n  %s\nexpected:\n  %s" %
+                         (msg, str(got).replace("\n", "\n  "),
+                          str(expect).replace("\n", "\n  ")))
+
+def assert_lines_match(text, *regexps, **kw):
+    """Assert that all of regexps match some line in text.  If a 'no'
+    keyword argument is given, it must be a list of regexps that must
+    *not* match any line in text."""
+
+    def assert_lines_match_kw(no=[]):
+        return no
+    no = assert_lines_match_kw(**kw)
+
+    # Check text against regexps
+    lines = text.splitlines()
+    good = set()
+    bad = set()
+    for i, line in enumerate(lines):
+        if any(re.match(r, line) for r in regexps):
+            good.add(i)
+            regexps = [r for r in regexps if not re.match(r, line)]
+        if any(re.match(r, line) for r in no):
+            bad.add(i)
+
+    if not regexps and not bad:
+        return
+
+    # We failed; construct an informative failure message
+    show = set()
+    for lineno in good.union(bad):
+        for offset in range(-2, 3):
+            show.add(lineno + offset)
+    if regexps:
+        show.update(n for n in range(len(lines) - 5, len(lines)))
+
+    msg = []
+    last = -1
+    for lineno in sorted(show):
+        if 0 <= lineno < len(lines):
+            if lineno != last + 1:
+                msg.append("...")
+            last = lineno
+            msg.append("%s %s" % (color("red", "BAD ") if lineno in bad else
+                                  color("green", "GOOD") if lineno in good
+                                  else "    ",
+                                  lines[lineno]))
+    if last != len(lines) - 1:
+        msg.append("...")
+    if bad:
+        msg.append("unexpected lines in output")
+    for r in regexps:
+        msg.append(color("red", "MISSING") + " '%s'" % r)
+    raise AssertionError("\n".join(msg))
+
+##################################################################
+# Utilities
+#
+
+__all__ += ["make", "maybe_unlink", "reset_fs", "color", "random_str", "check_time", "check_answers"]
+
+MAKE_TIMESTAMP = 0
+
+def pre_make():
+    """Delay prior to running make to ensure file mtimes change."""
+    while int(time.time()) == MAKE_TIMESTAMP:
+        time.sleep(0.1)
+
+def post_make():
+    """Record the time after make completes so that the next run of
+    make can be delayed if needed."""
+    global MAKE_TIMESTAMP
+    MAKE_TIMESTAMP = int(time.time())
+
+def make(*target):
+    pre_make()
+    if Popen(("make",) + target).wait():
+        sys.exit(1)
+    post_make()
+
+def show_command(cmd):
+    from pipes import quote
+    print("\n$", " ".join(map(quote, cmd)))
+
+def maybe_unlink(*paths):
+    for path in paths:
+        try:
+            os.unlink(path)
+        except EnvironmentError as e:
+            if e.errno != errno.ENOENT:
+                raise
+
+COLORS = {"default": "\033[0m", "red": "\033[31m", "green": "\033[32m"}
+
+def color(name, text):
+    if options.color == "always" or (options.color == "auto" and os.isatty(1)):
+        return COLORS[name] + text + COLORS["default"]
+    return text
+
+def reset_fs():
+    if os.path.exists("obj/fs/clean-fs.img"):
+        shutil.copyfile("obj/fs/clean-fs.img", "obj/fs/fs.img")
+
+def random_str(n=8):
+    letters = string.ascii_letters + string.digits
+    return ''.join(random.choice(letters) for _ in range(n))
+
+def check_time():
+    try:
+        print("")
+        with open('time.txt') as f:
+            d = f.read().strip()
+            if not re.match(r'^\d+$', d):
+                raise AssertionError('time.txt does not contain a single integer (number of hours spent on the lab)')
+    except IOError:
+        raise AssertionError('Cannot read time.txt')
+
+def check_answers(file, n=10):
+    try:
+        with open(file) as f:
+            d = f.read().strip()
+            if len(d) < n:
+                raise AssertionError('%s does not seem to contain enough text' % file)
+    except IOError:
+        raise AssertionError('Cannot read %s' % file)
+
+
+##################################################################
+# Controllers
+#
+
+__all__ += ["QEMU", "GDBClient"]
+
+class QEMU(object):
+    _GDBPORT = None
+
+    def __init__(self, *make_args):
+        # Check that QEMU is not currently running
+        try:
+            GDBClient(self.get_gdb_port(), timeout=0).close()
+        except socket.error:
+            pass
+        else:
+            print("""\
+GDB stub found on port %d.
+QEMU appears to already be running.  Please exit it if possible or use
+'killall qemu' or 'killall qemu.real'.""" % self.get_gdb_port(), file=sys.stderr)
+            sys.exit(1)
+
+        if options.verbose:
+            show_command(("make",) + make_args)
+        cmd = ("make", "-s", "--no-print-directory") + make_args
+        self.proc = Popen(cmd, stdout=subprocess.PIPE,
+                          stderr=subprocess.STDOUT,
+                          stdin=subprocess.PIPE)
+        # Accumulated output as a string
+        self.output = ""
+        # Accumulated output as a bytearray
+        self.outbytes = bytearray()
+        self.on_output = []
+
+    @staticmethod
+    def get_gdb_port():
+        if QEMU._GDBPORT is None:
+            p = Popen(["make", "-s", "--no-print-directory", "print-gdbport"],
+                      stdout=subprocess.PIPE)
+            (out, _) = p.communicate()
+            if p.returncode:
+                raise RuntimeError(
+                    "Failed to get gdbport: make exited with %d" %
+                    p.returncode)
+            QEMU._GDBPORT = int(out)
+        return QEMU._GDBPORT
+
+    def fileno(self):
+        if self.proc:
+            return self.proc.stdout.fileno()
+
+    def handle_read(self):
+        buf = os.read(self.proc.stdout.fileno(), 4096)
+        self.outbytes.extend(buf)
+        self.output = self.outbytes.decode("utf-8", "replace")
+        for callback in self.on_output:
+            callback(buf)
+        if buf == b"":
+            self.wait()
+            return
+
+    def write(self, buf):
+        if isinstance(buf, str):
+            buf = buf.encode('utf-8')
+        self.proc.stdin.write(buf)
+        self.proc.stdin.flush()
+
+    def wait(self):
+        if self.proc:
+            self.proc.wait()
+            self.proc = None
+
+    def kill(self):
+        if self.proc:
+            self.proc.terminate()
+
+class GDBClient(object):
+    def __init__(self, port, timeout=15):
+        start = time.time()
+        while True:
+            self.sock = socket.socket()
+            try:
+                self.sock.settimeout(1)
+                self.sock.connect(("localhost", port))
+                break
+            except socket.error:
+                if time.time() >= start + timeout:
+                    raise
+        self.__buf = ""
+
+    def fileno(self):
+        if self.sock:
+            return self.sock.fileno()
+
+    def handle_read(self):
+        try:
+            data = self.sock.recv(4096).decode("ascii", "replace")
+        except socket.error:
+            data = ""
+        if data == "":
+            self.sock.close()
+            self.sock = None
+            return
+        self.__buf += data
+
+        while True:
+            m = re.search(r"\$([^#]*)#[0-9a-zA-Z]{2}", self.__buf)
+            if not m:
+                break
+            pkt = m.group(1)
+            self.__buf = self.__buf[m.end():]
+
+            if pkt.startswith("T05"):
+                # Breakpoint
+                raise TerminateTest
+
+    def __send(self, cmd):
+        packet = "$%s#%02x" % (cmd, sum(map(ord, cmd)) % 256)
+        self.sock.sendall(packet.encode("ascii"))
+
+    def __send_break(self):
+        self.sock.sendall(b"\x03")
+
+    def close(self):
+        if self.sock:
+            self.sock.close()
+            self.sock = None
+
+    def cont(self):
+        self.__send("c")
+
+    def breakpoint(self, addr):
+        self.__send("Z1,%x,1" % addr)
+
+
+##################################################################
+# QEMU test runner
+#
+
+__all__ += ["TerminateTest", "Runner"]
+
+class TerminateTest(Exception):
+    pass
+
+class Runner():
+    def __init__(self, *default_monitors):
+        self.__default_monitors = default_monitors
+
+    def run_qemu(self, *monitors, **kw):
+        """Run a QEMU-based test.  monitors should functions that will
+        be called with this Runner instance once QEMU and GDB are
+        started.  Typically, they should register callbacks that throw
+        TerminateTest when stop events occur.  The target_base
+        argument gives the make target to run.  The make_args argument
+        should be a list of additional arguments to pass to make.  The
+        timeout argument bounds how long to run before returning."""
+
+        def run_qemu_kw(target_base="qemu", make_args=[], timeout=30):
+            return target_base, make_args, timeout
+        target_base, make_args, timeout = run_qemu_kw(**kw)
+
+        # Start QEMU
+        pre_make()
+        self.qemu = QEMU(target_base + "-gdb", *make_args)
+        self.gdb = None
+
+        try:
+            # Wait for QEMU to start or make to fail.  This will set
+            # self.gdb if QEMU starts.
+            self.qemu.on_output = [self.__monitor_start]
+            self.__react([self.qemu], timeout=90)
+            self.qemu.on_output = []
+            if self.gdb is None:
+                print("Failed to connect to QEMU; output:")
+                print(self.qemu.output)
+                sys.exit(1)
+            post_make()
+
+            # QEMU and GDB are up
+            self.reactors = [self.qemu, self.gdb]
+
+            # Start monitoring
+            for m in self.__default_monitors + monitors:
+                m(self)
+
+            # Run and react
+            self.gdb.cont()
+            self.__react(self.reactors, timeout)
+        finally:
+            # Shutdown QEMU
+            try:
+                if self.gdb is None:
+                    sys.exit(1)
+                self.qemu.kill()
+                self.__react(self.reactors, 5)
+                self.gdb.close()
+                self.qemu.wait()
+            except:
+                print("""\
+Failed to shutdown QEMU.  You might need to 'killall qemu' or
+'killall qemu.real'.
+""")
+                raise
+
+    def __monitor_start(self, output):
+        if b"\n" in output:
+            try:
+                self.gdb = GDBClient(self.qemu.get_gdb_port(), timeout=2)
+                raise TerminateTest
+            except socket.error:
+                pass
+        if not len(output):
+            raise TerminateTest
+
+    def __react(self, reactors, timeout):
+        deadline = time.time() + timeout
+        try:
+            while True:
+                timeleft = deadline - time.time()
+                if timeleft < 0:
+                    sys.stdout.write("Timeout! ")
+                    sys.stdout.flush()
+                    return
+
+                rset = [r for r in reactors if r.fileno() is not None]
+                if not rset:
+                    return
+
+                rset, _, _ = select.select(rset, [], [], timeleft)
+                for reactor in rset:
+                    reactor.handle_read()
+        except TerminateTest:
+            pass
+
+    def user_test(self, binary, *monitors, **kw):
+        """Run a user test using the specified binary.  Monitors and
+        keyword arguments are as for run_qemu.  This runs on a disk
+        snapshot unless the keyword argument 'snapshot' is False."""
+
+        maybe_unlink("obj/kern/init.o", "obj/kern/kernel")
+        if kw.pop("snapshot", True):
+            kw.setdefault("make_args", []).append("QEMUEXTRA+=-snapshot")
+        self.run_qemu(target_base="run-%s" % binary, *monitors, **kw)
+
+    def match(self, *args, **kwargs):
+        """Shortcut to call assert_lines_match on the most recent QEMU
+        output."""
+
+        assert_lines_match(self.qemu.output, *args, **kwargs)
+
+##################################################################
+# Monitors
+#
+
+__all__ += ["save", "stop_breakpoint", "call_on_line", "stop_on_line", "shell_script"]
+
+def save(path):
+    """Return a monitor that writes QEMU's output to path.  If the
+    test fails, copy the output to path.test-name."""
+
+    def setup_save(runner):
+        f.seek(0)
+        f.truncate()
+        runner.qemu.on_output.append(f.write)
+        get_current_test().on_finish.append(save_on_finish)
+
+    def save_on_finish(fail):
+        f.flush()
+        save_path = path + "." + get_current_test().__name__[5:]
+        if fail:
+            shutil.copyfile(path, save_path)
+            print("    QEMU output saved to %s" % save_path)
+        elif os.path.exists(save_path):
+            os.unlink(save_path)
+            print("    (Old %s failure log removed)" % save_path)
+
+    f = open(path, "wb")
+    return setup_save
+
+def stop_breakpoint(addr):
+    """Returns a monitor that stops when addr is reached.  addr may be
+    a number or the name of a symbol."""
+
+    def setup_breakpoint(runner):
+        if isinstance(addr, str):
+            addrs = [int(sym[:16], 16) for sym in open("kernel/kernel.sym")
+                     if sym[17:].strip() == addr]
+            assert len(addrs), "Symbol %s not found" % addr
+            runner.gdb.breakpoint(addrs[0])
+        else:
+            runner.gdb.breakpoint(addr)
+    return setup_breakpoint
+
+def call_on_line(regexp, callback):
+    """Returns a monitor that calls 'callback' when QEMU prints a line
+    matching 'regexp'."""
+
+    def setup_call_on_line(runner):
+        buf = bytearray()
+        def handle_output(output):
+            buf.extend(output)
+            while b"\n" in buf:
+                line, buf[:] = buf.split(b"\n", 1)
+                line = line.decode("utf-8", "replace")
+                if re.match(regexp, line):
+                    callback(line)
+        runner.qemu.on_output.append(handle_output)
+    return setup_call_on_line
+
+def stop_on_line(regexp):
+    """Returns a monitor that stops when QEMU prints a line matching
+    'regexp'."""
+
+    def stop(line):
+        raise TerminateTest
+    return call_on_line(regexp, stop)
+
+def shell_script(script, terminate_match=None):
+    """Returns a monitor that plays the script, and stops when the script is
+    done executing."""
+
+    def setup_call_on_line(runner):
+        class context:
+            n = 0
+            buf = bytearray()
+        def handle_output(output):
+            context.buf.extend(output)
+            if terminate_match is not None:
+                if re.match(terminate_match, context.buf.decode('utf-8', 'replace')):
+                    raise TerminateTest
+            if b'$ ' in context.buf:
+                context.buf = bytearray()
+                if context.n < len(script):
+                    runner.qemu.write(script[context.n])
+                    runner.qemu.write('\n')
+                    context.n += 1
+                else:
+                    if terminate_match is None:
+                        raise TerminateTest
+        runner.qemu.on_output.append(handle_output)
+    return setup_call_on_line

kernel/fcntl.h

@@ -3,3 +3,4 @@
 #define O_RDWR    0x002
 #define O_CREATE  0x200
 #define O_TRUNC   0x400
+#define O_NOFOLLOW 0x800

kernel/file.h

@@ -26,7 +26,7 @@ struct inode {
   short minor;
   short nlink;
   uint size;
-  uint addrs[NDIRECT+1];
+  uint addrs[NDIRECT+2];
 };
 
 // map major device number to device functions.

kernel/fs.c

@@ -416,7 +416,43 @@ bmap(struct inode *ip, uint bn)
     brelse(bp);
     return addr;
   }
-
+  bn -= NINDIRECT;
+  if (bn < NINDIRECT2) {
+    // Load doubly indirect block L1
+    if ((addr = ip->addrs[NDIRECT+1]) == 0){
+      addr = balloc(ip->dev);
+      if(addr == 0)
+        return 0;
+      ip->addrs[NDIRECT+1] = addr;
+    }
+    // load doubly indirect block L2
+    // we have NINDIRECT blocks for per L1 entry
+    bp = bread(ip->dev, addr);
+    a = (uint*)bp->data;
+    if ((addr = a[bn / NINDIRECT]) == 0) {
+      addr = balloc(ip->dev);
+      if (addr == 0) {
+        brelse(bp);
+        return 0;
+      }
+      a[bn / NINDIRECT] = addr;
+      log_write(bp);
+    }
+    brelse(bp);
+    // Load finally the target block
+    bp = bread(ip->dev, addr);
+    a = (uint*)bp->data;
+    if ((addr = a[bn % NINDIRECT]) == 0) {
+      addr = balloc(ip->dev);
+      if (addr) {
+        a[bn % NINDIRECT] = addr;
+        log_write(bp);
+      }
+    }
+    brelse(bp);
+    return addr;
+  }
+  printf("bn=%d\n", bn);
   panic("bmap: out of range");
 }
 
@@ -425,9 +461,9 @@ bmap(struct inode *ip, uint bn)
 void
 itrunc(struct inode *ip)
 {
-  int i, j;
+  int i, j, k;
-  struct buf *bp;
+  struct buf *bp, *bp1;
-  uint *a;
+  uint *a, *a1;
 
   for(i = 0; i < NDIRECT; i++){
     if(ip->addrs[i]){
@@ -448,6 +484,26 @@ itrunc(struct inode *ip)
     ip->addrs[NDIRECT] = 0;
   }
 
+  if (ip->addrs[NDIRECT+1]) {
+    bp = bread(ip->dev, ip->addrs[NDIRECT+1]);
+    a = (uint*)bp->data;
+    for(j = 0; j < NINDIRECT; j++){
+      if(a[j]) {
+        bp1 = bread(ip->dev, a[j]);
+        a1 = (uint*)bp1->data;
+        for (k = 0; k < NINDIRECT; ++ k) {
+          if (a1[k]) {
+            bfree(ip->dev, a1[k]);
+          }
+        }
+        brelse(bp1);
+        bfree(ip->dev, a[j]);
+      }
+    }
+    brelse(bp);
+    bfree(ip->dev, ip->addrs[NDIRECT+1]);
+    ip->addrs[NDIRECT+1] = 0;
+  }
   ip->size = 0;
   iupdate(ip);
 }

kernel/fs.h

@@ -24,9 +24,10 @@ struct superblock {
 
 #define FSMAGIC 0x10203040
 
-#define NDIRECT 12
+#define NDIRECT 11
 #define NINDIRECT (BSIZE / sizeof(uint))
-#define MAXFILE (NDIRECT + NINDIRECT)
+#define NINDIRECT2 (NINDIRECT * NINDIRECT)
+#define MAXFILE (NDIRECT + NINDIRECT + NINDIRECT2)
 
 // On-disk inode structure
 struct dinode {
@@ -35,7 +36,7 @@ struct dinode {
   short minor;          // Minor device number (T_DEVICE only)
   short nlink;          // Number of links to inode in file system
   uint size;            // Size of file (bytes)
-  uint addrs[NDIRECT+1];   // Data block addresses
+  uint addrs[NDIRECT+2];   // Data block addresses
 };
 
 // Inodes per block.

kernel/param.h

@@ -1,4 +1,8 @@
-#define NPROC        64  // maximum number of processes
+#ifdef LAB_FS
+#define NPROC        10  // maximum number of processes
+#else
+#define NPROC        64  // maximum number of processes (speedsup bigfile)
+#endif
 #define NCPU          8  // maximum number of CPUs
 #define NOFILE       16  // open files per process
 #define NFILE       100  // open files per system
@@ -9,5 +13,15 @@
 #define MAXOPBLOCKS  10  // max # of blocks any FS op writes
 #define LOGSIZE      (MAXOPBLOCKS*3)  // max data blocks in on-disk log
 #define NBUF         (MAXOPBLOCKS*3)  // size of disk block cache
-#define FSSIZE       2000  // size of file system in blocks
+#ifdef LAB_FS
+#define FSSIZE       200000  // size of file system in blocks
+#else
+#ifdef LAB_LOCK
+#define FSSIZE       10000  // size of file system in blocks
+#else
+#define FSSIZE       2000   // size of file system in blocks
+#endif
+#endif
 #define MAXPATH      128   // maximum file path name
+
+

kernel/stat.h

@@ -1,7 +1,7 @@
 #define T_DIR     1   // Directory
 #define T_FILE    2   // File
 #define T_DEVICE  3   // Device
-
+#define T_SYMLINK 4
 struct stat {
   int dev;     // File system's disk device
   uint ino;    // Inode number

kernel/syscall.c

@@ -101,6 +101,7 @@ extern uint64 sys_unlink(void);
 extern uint64 sys_link(void);
 extern uint64 sys_mkdir(void);
 extern uint64 sys_close(void);
+extern uint64 sys_symlink(void);
 
 // An array mapping syscall numbers from syscall.h
 // to the function that handles the system call.
@@ -126,6 +127,7 @@ static uint64 (*syscalls[])(void) = {
 [SYS_link]    sys_link,
 [SYS_mkdir]   sys_mkdir,
 [SYS_close]   sys_close,
+[SYS_symlink]   sys_symlink,
 };
 
 void

kernel/syscall.h

@@ -20,3 +20,4 @@
 #define SYS_link   19
 #define SYS_mkdir  20
 #define SYS_close  21
+#define SYS_symlink 22

kernel/sysfile.c

@@ -335,6 +335,36 @@ sys_open(void)
     }
   }
 
+  if (ip->type == T_SYMLINK && !(omode & O_NOFOLLOW)) {
+    int symlink_step = 0;
+    while (ip->type == T_SYMLINK) {
+      if (symlink_step++ > 10) {
+        // printf("\x1b[031mFailed\x1b[0m due to deep symlink\n");
+        iunlockput(ip); // on error, put inode 'cause only success open need to use the file after the syscall
+        end_op();
+        return -1;
+      }
+      int len_target = readi(ip, 0, (uint64)path, 0, MAXPATH);
+      iunlockput(ip); // no more need to use this inode
+      if (len_target == 0) {
+        printf("\x1b[031mFailed\x1b[0m to read symlink %s\n", path);
+        end_op();
+        return -1;
+      }
+      // get target's inode
+      if((ip = namei(path)) == 0){
+        // printf("\x1b[031mFailed\x1b[0m open symlink target %s\n", path);
+        end_op();
+        return -1;
+      }
+      ilock(ip);
+      if(ip->type == T_DIR && omode != O_RDONLY){
+        iunlockput(ip);
+        end_op();
+        return -1;
+      }
+    }
+  }
   if(ip->type == T_DEVICE && (ip->major < 0 || ip->major >= NDEV)){
     iunlockput(ip);
     end_op();
@@ -503,3 +533,32 @@ sys_pipe(void)
   }
   return 0;
 }
+
+uint64
+sys_symlink(void)
+{
+  char target[MAXPATH], path[MAXPATH];
+  int len_target, len_path;
+  struct inode* ip;
+  if ((len_target = argstr(0, target, MAXPATH)) < 0) 
+    return -1;
+  if ((len_path = argstr(1, path, MAXPATH)) < 0) 
+    return -1;
+  // printf("\x1b[033msys_symlink\x1b[0m %s -> %s\n", path, target);
+  begin_op();
+  ip = create(path, T_SYMLINK, 0, 0);
+  if (ip == 0) {
+    end_op();
+    // printf("\x1b[031mFailed\x1b[0m to create path %s\n", path);
+    return -1;
+  }
+  if (writei(ip, 0, (uint64)target, 0, len_target) != len_target) {
+    iunlockput(ip);
+    end_op();
+    printf("\x1b[031mFailed\x1b[0m to write symlink target %s to %s\n", target, path);
+    return -1;
+  }
+  iunlockput(ip); // no need to keep this inode ref, if not put, in-RAM inode pool will run out
+  end_op();
+  return 0;
+}

kernel/sysproc.c

@@ -55,6 +55,8 @@ sys_sleep(void)
   uint ticks0;
 
   argint(0, &n);
+  if(n < 0)
+    n = 0;
   acquire(&tickslock);
   ticks0 = ticks;
   while(ticks - ticks0 < n){

time.txt

@@ -0,0 +1 @@
+7

user/bigfile.c

@@ -0,0 +1,57 @@
+#include "kernel/types.h"
+#include "kernel/stat.h"
+#include "user/user.h"
+#include "kernel/fcntl.h"
+#include "kernel/fs.h"
+
+int
+main()
+{
+  char buf[BSIZE];
+  int fd, i, blocks;
+
+  fd = open("big.file", O_CREATE | O_WRONLY);
+  if(fd < 0){
+    printf("bigfile: cannot open big.file for writing\n");
+    exit(-1);
+  }
+
+  blocks = 0;
+  while(1){
+    *(int*)buf = blocks;
+    int cc = write(fd, buf, sizeof(buf));
+    if(cc <= 0)
+      break;
+    blocks++;
+    if (blocks % 100 == 0)
+      printf(".");
+  }
+
+  printf("\nwrote %d blocks\n", blocks);
+  if(blocks != 65803) {
+    printf("bigfile: file is too small\n");
+    exit(-1);
+  }
+  close(fd);
+  fd = open("big.file", O_RDONLY);
+  if(fd < 0){
+    printf("bigfile: cannot re-open big.file for reading\n");
+    exit(-1);
+  }
+  for(i = 0; i < blocks; i++){
+    int cc = read(fd, buf, sizeof(buf));
+    if(cc <= 0){
+      printf("bigfile: read error at block %d\n", i);
+      exit(-1);
+    }
+    if(*(int*)buf != i){
+      printf("bigfile: read the wrong data (%d) for block %d\n",
+             *(int*)buf, i);
+      exit(-1);
+    }
+  }
+
+  printf("bigfile done; ok\n"); 
+
+  exit(0);
+}

user/cat.c

@@ -1,5 +1,6 @@
 #include "kernel/types.h"
 #include "kernel/stat.h"
+#include "kernel/fcntl.h"
 #include "user/user.h"
 
 char buf[512];
@@ -32,7 +33,7 @@ main(int argc, char *argv[])
   }
 
   for(i = 1; i < argc; i++){
-    if((fd = open(argv[i], 0)) < 0){
+    if((fd = open(argv[i], O_RDONLY)) < 0){
       fprintf(2, "cat: cannot open %s\n", argv[i]);
       exit(1);
     }

user/grep.c

@@ -2,6 +2,7 @@
 
 #include "kernel/types.h"
 #include "kernel/stat.h"
+#include "kernel/fcntl.h"
 #include "user/user.h"
 
 char buf[1024];
@@ -51,7 +52,7 @@ main(int argc, char *argv[])
   }
 
   for(i = 2; i < argc; i++){
-    if((fd = open(argv[i], 0)) < 0){
+    if((fd = open(argv[i], O_RDONLY)) < 0){
       printf("grep: cannot open %s\n", argv[i]);
       exit(1);
     }

user/ls.c

@@ -2,6 +2,7 @@
 #include "kernel/stat.h"
 #include "user/user.h"
 #include "kernel/fs.h"
+#include "kernel/fcntl.h"
 
 char*
 fmtname(char *path)
@@ -30,7 +31,7 @@ ls(char *path)
   struct dirent de;
   struct stat st;
 
-  if((fd = open(path, 0)) < 0){
+  if((fd = open(path, O_RDONLY)) < 0){
     fprintf(2, "ls: cannot open %s\n", path);
     return;
   }

user/symlinktest.c

@@ -0,0 +1,188 @@
+#include "kernel/param.h"
+#include "kernel/types.h"
+#include "kernel/stat.h"
+#include "kernel/riscv.h"
+#include "kernel/fcntl.h"
+#include "kernel/spinlock.h"
+#include "kernel/sleeplock.h"
+#include "kernel/fs.h"
+#include "kernel/file.h"
+#include "user/user.h"
+
+#define fail(msg) do {printf("FAILURE: " msg "\n"); failed = 1; goto done;} while (0);
+static int failed = 0;
+
+static void testsymlink(void);
+static void concur(void);
+static void cleanup(void);
+
+int
+main(int argc, char *argv[])
+{
+  cleanup();
+  testsymlink();
+  concur();
+  exit(failed);
+}
+
+static void
+cleanup(void)
+{
+  unlink("/testsymlink/a");
+  unlink("/testsymlink/b");
+  unlink("/testsymlink/c");
+  unlink("/testsymlink/1");
+  unlink("/testsymlink/2");
+  unlink("/testsymlink/3");
+  unlink("/testsymlink/4");
+  unlink("/testsymlink/z");
+  unlink("/testsymlink/y");
+  unlink("/testsymlink");
+}
+
+// stat a symbolic link using O_NOFOLLOW
+static int
+stat_slink(char *pn, struct stat *st)
+{
+  int fd = open(pn, O_RDONLY | O_NOFOLLOW);
+  if(fd < 0)
+    return -1;
+  if(fstat(fd, st) != 0)
+    return -1;
+  return 0;
+}
+
+static void
+testsymlink(void)
+{
+  int r, fd1 = -1, fd2 = -1;
+  char buf[4] = {'a', 'b', 'c', 'd'};
+  char c = 0, c2 = 0;
+  struct stat st;
+    
+  printf("Start: test symlinks\n");
+
+  mkdir("/testsymlink");
+
+  fd1 = open("/testsymlink/a", O_CREATE | O_RDWR);
+  if(fd1 < 0) fail("failed to open a");
+
+  r = symlink("/testsymlink/a", "/testsymlink/b");
+  if(r < 0)
+    fail("symlink b -> a failed");
+
+  if(write(fd1, buf, sizeof(buf)) != 4)
+    fail("failed to write to a");
+
+  if (stat_slink("/testsymlink/b", &st) != 0)
+    fail("failed to stat b");
+  if(st.type != T_SYMLINK)
+    fail("b isn't a symlink");
+
+  fd2 = open("/testsymlink/b", O_RDWR);
+  if(fd2 < 0)
+    fail("failed to open b");
+  read(fd2, &c, 1);
+  if (c != 'a')
+    fail("failed to read bytes from b");
+
+  unlink("/testsymlink/a");
+  if(open("/testsymlink/b", O_RDWR) >= 0)
+    fail("Should not be able to open b after deleting a");
+
+  r = symlink("/testsymlink/b", "/testsymlink/a");
+  if(r < 0)
+    fail("symlink a -> b failed");
+
+  r = open("/testsymlink/b", O_RDWR);
+  if(r >= 0)
+    fail("Should not be able to open b (cycle b->a->b->..)\n");
+  
+  r = symlink("/testsymlink/nonexistent", "/testsymlink/c");
+  if(r != 0)
+    fail("Symlinking to nonexistent file should succeed\n");
+
+  r = symlink("/testsymlink/2", "/testsymlink/1");
+  if(r) fail("Failed to link 1->2");
+  r = symlink("/testsymlink/3", "/testsymlink/2");
+  if(r) fail("Failed to link 2->3");
+  r = symlink("/testsymlink/4", "/testsymlink/3");
+  if(r) fail("Failed to link 3->4");
+
+  close(fd1);
+  close(fd2);
+
+  fd1 = open("/testsymlink/4", O_CREATE | O_RDWR);
+  if(fd1<0) fail("Failed to create 4\n");
+  fd2 = open("/testsymlink/1", O_RDWR);
+  if(fd2<0) fail("Failed to open 1\n");
+
+  c = '#';
+  r = write(fd2, &c, 1);
+  if(r!=1) fail("Failed to write to 1\n");
+  r = read(fd1, &c2, 1);
+  if(r!=1) fail("Failed to read from 4\n");
+  if(c!=c2)
+    fail("Value read from 4 differed from value written to 1\n");
+
+  printf("test symlinks: ok\n");
+done:
+  close(fd1);
+  close(fd2);
+}
+
+static void
+concur(void)
+{
+  int pid, i;
+  int fd;
+  struct stat st;
+  int nchild = 2;
+
+  printf("Start: test concurrent symlinks\n");
+    
+  fd = open("/testsymlink/z", O_CREATE | O_RDWR);
+  if(fd < 0) {
+    printf("FAILED: open failed");
+    exit(1);
+  }
+  close(fd);
+
+  for(int j = 0; j < nchild; j++) {
+    pid = fork();
+    if(pid < 0){
+      printf("FAILED: fork failed\n");
+      exit(1);
+    }
+    if(pid == 0) {
+      int m = 0;
+      unsigned int x = (pid ? 1 : 97);
+      for(i = 0; i < 100; i++){
+        x = x * 1103515245 + 12345;
+        if((x % 3) == 0) {
+          symlink("/testsymlink/z", "/testsymlink/y");
+          if (stat_slink("/testsymlink/y", &st) == 0) {
+            m++;
+            if(st.type != T_SYMLINK) {
+              printf("FAILED: not a symbolic link\n", st.type);
+              exit(1);
+            }
+          }
+        } else {
+          unlink("/testsymlink/y");
+        }
+      }
+      exit(0);
+    }
+  }
+
+  int r;
+  for(int j = 0; j < nchild; j++) {
+    wait(&r);
+    if(r != 0) {
+      printf("test concurrent symlinks: failed\n");
+      exit(1);
+    }
+  }
+  printf("test concurrent symlinks: ok\n");
+}

user/user.h

@@ -22,6 +22,7 @@ int getpid(void);
 char* sbrk(int);
 int sleep(int);
 int uptime(void);
+int symlink(char* target, char* path);
 
 // ulib.c
 int stat(const char*, struct stat*);

user/usys.pl

@@ -36,3 +36,4 @@ entry("getpid");
 entry("sbrk");
 entry("sleep");
 entry("uptime");
+entry("symlink");

user/wc.c

@@ -1,5 +1,6 @@
 #include "kernel/types.h"
 #include "kernel/stat.h"
+#include "kernel/fcntl.h"
 #include "user/user.h"
 
 char buf[512];
@@ -43,7 +44,7 @@ main(int argc, char *argv[])
   }
 
   for(i = 1; i < argc; i++){
-    if((fd = open(argv[i], 0)) < 0){
+    if((fd = open(argv[i], O_RDONLY)) < 0){
       printf("wc: cannot open %s\n", argv[i]);
       exit(1);
     }