Checkpoint some warm-up exercises
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Frans Kaashoek
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labs/xv6.html
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<html>
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<head>
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<title>Homework: xv6</title>
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<link rel="stylesheet" href="homework.css" type="text/css" />
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</head>
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<body>
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<h1>Lab: xv6</h1>
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This lab makes you familiar with xv6 and its system calls.
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<h2>Boot xv6</h2>
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<p>Login to Athena (e.g., ssh -X athena.dialup.mit.edu) and attach the course
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locker: (You must run this command every time you log in; or add it to your
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~/.environment file.)
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<pre>
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$ add -f 6.828
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</pre>
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<p>Fetch the xv6 source:
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<pre>
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$ mkdir 6.828
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$ cd 6.828
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$ git clone git://github.com/mit-pdos/xv6-riscv.git
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Cloning into 'xv6-riscv'...
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...
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$
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</pre>
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<p>XXX pointer to an update tools page
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<p>Build xv6 on Athena:
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<pre>
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$ cd xv6-public
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$ makeriscv64-linux-gnu-gcc -c -o kernel/entry.o kernel/entry.S
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riscv64-linux-gnu-gcc -Wall -Werror -O -fno-omit-frame-pointer -ggdb -MD -mcmodel=medany -ffreestanding -fno-common -nostdlib -mno-relax -I. -fno-stack-protector -fno-pie -no-pie -c -o kernel/start.o kernel/start.c
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...
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$ make qemu
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...
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mkfs/mkfs fs.img README user/_cat user/_echo user/_forktest user/_grep user/_init user/_kill user/_ln user/_ls user/_mkdir user/_rm user/_sh user/_stressfs user/_usertests user/_wc user/_zombie user/_cow
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nmeta 46 (boot, super, log blocks 30 inode blocks 13, bitmap blocks 1) blocks 954 total 1000
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balloc: first 497 blocks have been allocated
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balloc: write bitmap block at sector 45
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qemu-system-riscv64 -machine virt -kernel kernel/kernel -m 3G -smp 3 -nographic -drive file=fs.img,if=none,format=raw,id=x0 -device virtio-blk-device,drive=x0,bus=virtio-mmio-bus.0
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hart 0 starting
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hart 2 starting
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hart 1 starting
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init: starting sh
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$
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</pre>
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<p>
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If you type <tt>ls</tt> at the prompt, you should output similar to the following:
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<pre>
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$ ls
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. 1 1 1024
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.. 1 1 1024
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README 2 2 2181
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cat 2 3 21024
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echo 2 4 19776
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forktest 2 5 11456
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grep 2 6 24512
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init 2 7 20656
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kill 2 8 19856
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ln 2 9 19832
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ls 2 10 23280
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mkdir 2 11 19952
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rm 2 12 19936
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sh 2 13 38632
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stressfs 2 14 20912
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usertests 2 15 106264
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wc 2 16 22160
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zombie 2 17 19376
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cow 2 18 27152
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console 3 19 0
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</pre>
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These are the programs/files that <tt>mkfs</tt> includes in the
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initial file system. You just ran one of them: <tt>ls</tt>.
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<h2>sleep</h2>
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<p>Write a program that sleeps for a user-specified number of seconds,
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compile it, and run it.
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<p>Some hints:
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<ul>
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<li>Look at some of the other programs in <tt>user/</tt> to see
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how you can obtain the arguments passed to a program. If the user
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forgets to pass an argument, sleep should print an error message.
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<li>The argument is passed as a string; you can convert it to an
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integer using <tt>atoi</tt> (see user/ulib.c).
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<li>Use the system call <tt>sleep</tt> (see user/usys.S).
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<li>Make sure <tt>main</tt> calls <tt>exit()</tt> in order to exit
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your program.
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<li>Add the program to <tt>UPROGS</tt> in Makefile and compile
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user programs by typing <tt>make fs.img</tt>.
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</ul>
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<p>Run the program from the xv6 shell:
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<pre>
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$ make qemu
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...
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init: starting sh
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$ sleep 5
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(waits for a little while)
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$
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</pre>
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<p>Optional: write an uptime program that prints the uptime in terms
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of ticks using the <tt>uptime</tt> system call.
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<h2>pingpong</h2>
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<p>In the previous exercise, if you made an error in sleep, the
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program may have exited prematurely, but it didn't affect other
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processes because xv6 isolates processes. Sometimes you want
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processes to interact with each other. Xv6 provides two ways to do:
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either through the file system (one process can create a file and
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another process can read that file) or through pipes. In this
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exercise you explore interprocess communication through pipes.
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<p> Write a program that uses UNIX system calls to ``ping-pong'' a
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byte between two processes over a pair of pipes, one for each
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direction. The parent sends by writing a byte to <tt>fd[1]</tt> and
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the child receives it by reading from <tt>fd[0]</tt>. After
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receiving a byte from parent, the child responds with its own byte
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by writing to <tt>fd[1]</tt>, which the parent then reads.
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<p>Some hints:
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<ul>
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<li>Use <tt>pipe</tt> to create a pipe.
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<li>Use <tt>fork</tt> to create a child.
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<li>Use <tt>read</tt> to read from the pipe, and <tt>write</tt> to write to the pipe.
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</ul>
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<h2>find</h2>
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<h2>Optional: modify shell</h2>
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<p>Modify the shell to support lists of commands, separated by ";"
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<p>Modify the shell to support sub-shells by implementing "(" and ")"
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</body>
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</html>
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