In this assignment you will add support for tracking when a file was created to the xv6 filesystem. We will also add support to the ls and mkfs utilities so that they display and create timestamps, respectively.
As usual, we'll be working off of a slightly modified version of xv6. The only difference is that the date.h header, which you will need in order to get the current time, has been modified so that it can be included multiple times without causing a compile error.
If you still have your xv6 directory from last time, remove or rename it first. Then get the base xv6 code for this assignment:
$ git clone https://github.com/moyix/xv6-public.git
Cloning into 'xv6-public'...
remote: Counting objects: 4517, done.
remote: Compressing objects: 100% (5/5), done.
remote: Total 4517 (delta 1), reused 0 (delta 0), pack-reused 4512
Receiving objects: 100% (4517/4517), 11.67 MiB | 6.31 MiB/s, done.
Resolving deltas: 100% (1825/1825), done.
Checking connectivity... done.
$ cd xv6-public/
$ git checkout hw7
Branch hw7 set up to track remote branch hw7 from origin.
Switched to a new branch 'hw7'In xv6, each file and directory is associate with an i-node, a structure that keeps track of details such as the file's type (file, directory, or device), reference count, and list of disk blocks. i-nodes are stored both on disk (in a struct dinode) and in memory (struct inode), and xv6 copies data between the two structures as needed.
Modify the filesystem code so that on-disk and in-memory i-nodes both contain a field that keeps track of the time the i-node was created. Make sure that you modify both the on-disk and in-memory i-node structures, and that when xv6 copies data between then you also copy the creation time.
You can verify that you did this part correctly by using gdb to examine a newly created i-node and making sure that it contains the correct timestamp (or just do part 2, which modifies the ls command to print out timestamps as well).
Hints
create() function in sysfile.c.cmostime() function to get the current date and time from inside of xv6.struct dinode must divide the block size evenly. So when you add in the timestamp field, you will have to pad out the structure somehow (perhaps by increasing the number of direct block pointers).Modify the ls command so that it prints out the creation time of each file or directory.
sb: size 1000 nblocks 916 ninodes 200 nlog 30 logstart 2 inodestart 32
bmap start 83
init: starting sh
$ ls
. 1 1 512 0/0/0 00:00:00
.. 1 1 512 0/0/0 00:00:00
README 2 2 1972 0/0/0 00:00:00
cat 2 3 13420 0/0/0 00:00:00
echo 2 4 12525 0/0/0 00:00:00
forktest 2 5 8257 0/0/0 00:00:00
grep 2 6 15088 0/0/0 00:00:00
init 2 7 13190 0/0/0 00:00:00
kill 2 8 12677 0/0/0 00:00:00
ln 2 9 12531 0/0/0 00:00:00
ls 2 10 15259 0/0/0 00:00:00
mkdir 2 11 12678 0/0/0 00:00:00
rm 2 12 12659 0/0/0 00:00:00
sh 2 13 23639 0/0/0 00:00:00
stressfs 2 14 13401 0/0/0 00:00:00
usertests 2 15 58688 0/0/0 00:00:00
wc 2 16 13938 0/0/0 00:00:00
zombie 2 17 12295 0/0/0 00:00:00
console 3 18 0 11/20/2015 23:08:00
$ echo hello > file.txt
$ ls file.txt
file.txt 2 19 3 11/21/2015 23:14:02Hints:
ls uses the fstat call to retrieve information about the file or directory; you will need to modify the implementation of fstat so that it returns information about the creation time as well.You may have noticed that many of the files on the filesystem have a creation time of 0/0/0 00:00:00. This is because the initial filesystem image (fs.img) is not created from within xv6, but rather by the mkfs program, which is run outside of xv6 by the Makefile.
To finish up the implementation, modify mkfs.c so that it writes the current timestamp into the on-disk i-node when the initial filesystem image is created. Verify that when you boot xv6, you now get a directory listing that looks like:
$ ls
. 1 1 512 11/22/2015 00:00:29
.. 1 1 512 11/22/2015 00:00:29
README 2 2 1972 11/22/2015 00:00:29
cat 2 3 13420 11/22/2015 00:00:29
echo 2 4 12525 11/22/2015 00:00:29
forktest 2 5 8257 11/22/2015 00:00:29
grep 2 6 15088 11/22/2015 00:00:29
init 2 7 13190 11/22/2015 00:00:29
kill 2 8 12677 11/22/2015 00:00:29
ln 2 9 12531 11/22/2015 00:00:29
ls 2 10 15631 11/22/2015 00:00:29
mkdir 2 11 12678 11/22/2015 00:00:29
rm 2 12 12659 11/22/2015 00:00:29
sh 2 13 23639 11/22/2015 00:00:29
stressfs 2 14 13401 11/22/2015 00:00:29
usertests 2 15 58688 11/22/2015 00:00:29
wc 2 16 13938 11/22/2015 00:00:29
zombie 2 17 12295 11/22/2015 00:00:29
console 3 18 0 11/22/2015 00:00:32Hints:
gmtime() function helpful.make clean in order to remove the old fs.img and re-run make before the timestamps show up correctly (or just run rm fs.img).As with previous assignments, you will use git to create a patch.
Commit your changes:
$ git commit --all --message="Add filesystem timestamps"
[hw7 b778e43] Add filesystem timestamps
7 files changed, 31 insertions(+), 3 deletions(-)(Note: if you added any new files, you will also have to use git add <filename> before you run git commit.)
Now create the patch file:
$ git format-patch hw7.unmodified
0001-Add-filesystem-timestamps.patchThe command creates a file, 0001-Add-filesystem-timestamps.patch, containing the changes you've made. Submit this file on NYU Classes, along with a partner.txt listing your partner (if any).
Submission Notes
Don't try to edit the patch file after creating it. Doing so will most likely corrupt the patch file and make it impossible to apply. Instead, change the original file, commit your changes, and run git format-patch again:
$ git commit --all --message="Description of your change here"
[hw7 7cc4977] Description of your change here
1 file changed, 1 insertion(+), 1 deletion(-)
$ git format-patch hw7.unmodified
0001-Add-filesystem-timestamps.patch
0002-Description-of-your-change-here.patchThen submit both patch files.