Fetch the xv6 source for the lab and check out the mmap branch:
$ git fetch $ git checkout mmap $ make clean
The manual page (run man 2 mmap) shows this declaration for mmap:
void *mmap(void *addr, size_t length, int prot, int flags, int fd, off_t offset);
mmap can be called in many ways, but this lab requires only a subset of its features relevant to memory-mapping a file. You can assume that addr will always be zero, meaning that the kernel should decide the virtual address at which to map the file. mmap returns that address, or 0xffffffffffffffff if it fails. length is the number of bytes to map; it might not be the same as the file's length. prot indicates whether the memory should be mapped readable, writeable, and/or executable; you can assume that prot is PROT_READ or PROT_WRITE or both. flags will be either MAP_SHARED, meaning that modifications to the mapped memory should be written back to the file, or MAP_PRIVATE, meaning that they should not. You don't have to implement any other bits in flags. fd is the open file descriptor of the file to map. You can assume offset is zero (it's the starting point in the file at which to map).
It's OK if processes that map the same MAP_SHARED file do not share physical pages.
munmap(addr, length) should remove mmap mappings in the indicated address range. If the process has modified the memory and has it mapped MAP_SHARED, the modifications should first be written to the file. An munmap call might cover only a portion of an mmap-ed region, but you can assume that it will either unmap at the start, or at the end, or the whole region (but not punch a hole in the middle of a region).
You should implement enough mmap and munmap functionality to make the mmaptest test program work. If mmaptest doesn't use a mmap feature, you don't need to implement that feature.
When you're done, you should see this output:
$ mmaptest mmap_test starting test mmap f test mmap f: OK test mmap private test mmap private: OK test mmap read-only test mmap read-only: OK test mmap read/write test mmap read/write: OK test mmap dirty test mmap dirty: OK test not-mapped unmap test not-mapped unmap: OK test mmap two files test mmap two files: OK mmap_test: ALL OK fork_test starting fork_test OK mmaptest: all tests succeeded $ usertests usertests starting ... ALL TESTS PASSED $
Here are some hints:
Run usertests to make sure everything still works.
This completes the lab. Make sure you pass all of the make
grade tests. If this lab had questions, don't forget to write up your
answers to the questions in answers-lab-name.txt. Commit your changes
(including adding answers-lab-name.txt) and type make handin in the lab
directory to hand in your lab.
Create a new file, time.txt, and put in it a single integer, the
number of hours you spent on the lab. Don't forget to git add and
git commit the file.
Submit the lab
You will turn in your assignments using
website. You need to request once an API key from the submission
website before you can turn in any assignments or labs.
This completes the lab. Make sure you pass all of the make grade tests. If this lab had questions, don't forget to write up your answers to the questions in answers-lab-name.txt. Commit your changes (including adding answers-lab-name.txt) and type make handin in the lab directory to hand in your lab.
Create a new file, time.txt, and put in it a single integer, the number of hours you spent on the lab. Don't forget to git add and git commit the file.
After committing your final changes to the lab, type make handin to submit your lab.
$ git commit -am "ready to submit my lab" [util c2e3c8b] ready to submit my lab 2 files changed, 18 insertions(+), 2 deletions(-) $ make handin tar: Removing leading `/' from member names Get an API key for yourself by visiting https://6828.scripts.mit.edu/2020/handin.py/ Please enter your API key: XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX % Total % Received % Xferd Average Speed Time Time Time Current Dload Upload Total Spent Left Speed 100 79258 100 239 100 79019 853 275k --:--:-- --:--:-- --:--:-- 276k $make handin will store your API key in myapi.key. If you need to change your API key, just remove this file and let make handin generate it again (myapi.key must not include newline characters).
If you run make handin and you have either uncomitted changes or untracked files, you will see output similar to the following:
M hello.c ?? bar.c ?? foo.pyc Untracked files will not be handed in. Continue? [y/N]Inspect the above lines and make sure all files that your lab solution needs are tracked i.e. not listed in a line that begins with ??. You can cause git to track a new file that you create using git add filename.
If make handin does not work properly, try fixing the problem with the curl or Git commands. Or you can run make tarball. This will make a tar file for you, which you can then upload via our web interface.