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diff --git a/labs/xv6.html b/labs/xv6.html new file mode 100644 index 0000000..13d581e --- /dev/null +++ b/labs/xv6.html @@ -0,0 +1,238 @@ +<html> +<head> +<title>Lab: xv6</title> +<link rel="stylesheet" href="homework.css" type="text/css" /> +</head> +<body> + +<h1>Lab: xv6</h1> + +This lab makes you familiar with xv6 and its system calls. + +<h2>Boot xv6</h2> + +<p>Login to Athena (e.g., ssh -X athena.dialup.mit.edu) and attach the course +locker: (You must run this command every time you log in; or add it to your +~/.environment file.) + +<pre> +$ add -f 6.828 +</pre> + +<p>Fetch the xv6 source: + +<pre> +$ mkdir 6.828 +$ cd 6.828 +$ git clone git://github.com/mit-pdos/xv6-riscv.git +Cloning into 'xv6-riscv'... +... +$ +</pre> + +<p>XXX pointer to an update tools page + +<p>Build xv6 on Athena: +<pre> +$ cd xv6-public +$ makeriscv64-linux-gnu-gcc -c -o kernel/entry.o kernel/entry.S +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 +... +$ make qemu +... +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 +nmeta 46 (boot, super, log blocks 30 inode blocks 13, bitmap blocks 1) blocks 954 total 1000 +balloc: first 497 blocks have been allocated +balloc: write bitmap block at sector 45 +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 +hart 0 starting +hart 2 starting +hart 1 starting +init: starting sh +$ +</pre> + +<p> +If you type <tt>ls</tt> at the prompt, you should output similar to the following: +<pre> +$ ls +. 1 1 1024 +.. 1 1 1024 +README 2 2 2181 +cat 2 3 21024 +echo 2 4 19776 +forktest 2 5 11456 +grep 2 6 24512 +init 2 7 20656 +kill 2 8 19856 +ln 2 9 19832 +ls 2 10 23280 +mkdir 2 11 19952 +rm 2 12 19936 +sh 2 13 38632 +stressfs 2 14 20912 +usertests 2 15 106264 +wc 2 16 22160 +zombie 2 17 19376 +cow 2 18 27152 +console 3 19 0 +</pre> +These are the programs/files that <tt>mkfs</tt> includes in the +initial file system. You just ran one of them: <tt>ls</tt>. + +<h2>sleep</h2> + +<p>Implement the UNIX program sleep for xv6; your sleep should pause + for a user-specified number of ticks. + +<p>Some hints: + <ul> + <li>Look at some of the other programs in <tt>user/</tt> to see + how you can obtain the command-line arguments passed to a program. If the user + forgets to pass an argument, sleep should print an error message. + + <li>The command-line argument is passed as a string; you can convert it to an + integer using <tt>atoi</tt> (see user/ulib.c). + + <li>Use the system call <tt>sleep</tt> (see user/usys.S and kernel/sysproc.c). + + <li>Make sure <tt>main</tt> calls <tt>exit()</tt> in order to exit + your program. + + <li>Add the program to <tt>UPROGS</tt> in Makefile and compile + user programs by typing <tt>make fs.img</tt>. + + </ul> + + <p>Run the program from the xv6 shell: + <pre> + $ make qemu + ... + init: starting sh + $ sleep 10 + (waits for a little while) + $ + </pre> + + <p>Optional: write an uptime program that prints the uptime in terms + of ticks using the <tt>uptime</tt> system call. + +<h2>pingpong</h2> + +<p> Write a program that uses UNIX system calls to ``ping-pong'' a + byte between two processes over a pair of pipes, one for each + direction. The parent sends by writing a byte to <tt>fd[1]</tt> and + the child receives it by reading from <tt>fd[0]</tt>. After + receiving a byte from parent, the child responds with its own byte + by writing to <tt>fd[1]</tt>, which the parent then reads. + +<p>Some hints: + <ul> + <li>Use <tt>pipe</tt> to create a pipe. + <li>Use <tt>fork</tt> to create a child. + <li>Use <tt>read</tt> to read from the pipe, and <tt>write</tt> to write to the pipe. + </ul> + +<h2>primes</h2> + + <p>Write a concurrent version of prime sieve using pipes. This idea + is due to Doug McIlroy, inventor of Unix pipes. The picture + halfway down <a href="http://swtch.com/~rsc/thread/">the page</a> + and the text surrounding it explain how to do it. + + <p>Your goal is to use <tt>pipe</tt> and <tt>fork</tt> to set up + the pipeline. The first process feeds the numbers 2 through 35 + into the pipeline. For each prime number, you will arrange to + create one process that reads from its left neighbor over a pipe + and writes to its right neighbor over another pipe. Since xv6 has + limited number of file descriptors and processes, the first + process can stop at 35. + +<p>Some hints: + <ul> + <li>Be careful to close file descriptors that a process doesn't + need, because otherwise your program will run xv6 out of resources + before the first process reaches 35. + + <li>Once the first process reach 35, you should arrange that the + pipeline terminates cleanly (Hint: read will return an end-of-file + when the write-side of the pipe is closed). + </ul> + +<h2>find</h2> + +<p>Write a simple version of the UNIX find program: find all the files + in a directory tree whose name matches a string. For example if the + file system contains a file <tt>a/b</tt>, then running find as + follows should produce: + <pre> + $ find . b + ./a/b + $ + </pre> + +<p>Some hints: + <ul> + <li>Look at user/ls.c to see how to read directories. + <li>Use recursion to run find in sub-directories. + <li>Don't recurse into "." and "..". + </ul> + +<p>Optional: support regular expressions in name matching. Grep has some + primitive support for regular expressions. + +<h2>xargs</h2> + +<p>Write a simple version of the UNIX xargs program: read lines from + standard in and run a command for each line, supplying the line as + arguments to the command. The following example illustrates xarg's + behavior: + <pre> + $ xargs echo bye + hello too + bye hello too + <ctrl-d> + $ + </pre> + Note that the command here is "echo bye" and the additional + arguments are "hello too", making the command "echo bye hello too", + which outputs "bye hello too". + +<p>xargs and find combine well: + <pre> + find . b | xargs grep hello + </pre> + will run "grep hello" on each file named b in the directories below ".". + +<p>Some hints: + <ul> + <li>Use <tt>fork</tt> and <tt>exec</tt> system call to invoke the + command on each line of input. Use <tt>wait</tt> in the parent + to wait for the child to complete running the command. + <li>Read from stdin a character at the time until the newline + character ('\n'). + <li>kernel/param.h declares MAXARG, which may be useful if you need + to declare an argv. + </ul> + +<h2>Optional: modify the shell</h2> + +There are endless ways in which the shell could be extended. Here are +some suggestions: + +<ul> + +<li>Modify the shell to support wait. + +<li>Modify the shell to support lists of commands, separated by ";" + +<li>Modify the shell to support sub-shells by implementing "(" and ")" + +<li>Modify the shell to allow users to edit the command line + +</ul> + +</body> +</html> + + |