X-Git-Url: https://pintos-os.org/cgi-bin/gitweb.cgi?a=blobdiff_plain;ds=sidebyside;f=TODO;h=88a08331a6224dd9a0c56163c0bc79a8f6b71f1a;hb=0c02ec53400c7c8ec2c60d09b71c64625f61d073;hp=85bd51a0a73484bc5c9940c88fb705bfbbec40c6;hpb=3389cbb515f92b56550c41b1ca0bda9d4a6fbf9e;p=pintos-anon diff --git a/TODO b/TODO index 85bd51a..88a0833 100644 --- a/TODO +++ b/TODO @@ -1,36 +1,105 @@ -*- text -*- +Godmar says: + +- In Project 2, we're missing tests that pass arguments to system calls +that span multiple pages, where some are mapped and some are not. +An implementation that only checks the first page, rather than all pages +that can be touched during a call to read()/write() passes all tests. + +- In Project 2, we're missing a test that would fail if they assumed +that contiguous user-virtual addresses are laid out contiguously +in memory. The loading code should ensure that non-contiguous +physical pages are allocated for the data segment (at least.) + +- Need some tests that test that illegal accesses lead to process +termination. I have written some, will add them. In P2, obviously, +this would require that the students break this functionality since +the page directory is initialized for them, still it would be good +to have. + +- There does not appear to be a test that checks that they close all +fd's on exit. Idea: add statistics & self-diagnostics code to palloc.c +and malloc.c. Self-diagnostics code could be used for debugging. +The statistics code would report how much kernel memory is free. +Add a system call "get_kernel_memory_information". User programs +could engage in a variety of activities and notice leaks by checking +the kernel memory statistics. + +--- + From: "Godmar Back" -Subject: thread_yield in irq handler +Subject: priority donation tests To: "Ben Pfaff" -Date: Wed, 22 Feb 2006 22:18:50 -0500 +Date: Fri, 3 Mar 2006 11:02:08 -0500 Ben, -you write in your Tour of Pintos: +it seems the priority donation tests are somewhat incomplete and allow +incorrect implementations to pass with a perfect score. -"Second, an interrupt handler must not call any function that can -sleep, which rules out thread_yield(), lock_acquire(), and many -others. This is because external interrupts use space on the stack of -the kernel thread that was running at the time the interrupt occurred. -If the interrupt handler tried to sleep and that thread resumed, then -the two uses of the single stack would interfere, which cannot be -allowed." +We are seeing the following wrong implementations pass all tests: -Is the last sentence really true? +- Implementations that assume locks are released in the opposite order +in which they're acquired. The students implement this by +popping/pushing on the donation list. -I thought the reason that you couldn't sleep is that you would put -effectively a random thread/process to sleep, but I don't think it -would cause problems with the kernel stack. After all, it doesn't -cause this problem if you call thread_yield at the end of -intr_handler(), so why would it cause this problem earlier. +- Implementations that assume that the priority of a thread waiting on +a semaphore or condition variable cannot change between when the +thread was blocked and when it is unblocked. The students implement +this by doing an insert into an ordered list on block, rather than +picking the maximum thread on unblock. -As for thread_yield(), my understanding is that the reason it's called -at the end is to ensure it's done after the interrupt is acknowledged, -which you can't do until the end because Pintos doesn't handle nested -interrupts. +Neither of these two cases is detected; do you currently check for +these mistakes manually? - - Godmar +I wrote a test that checks for the first case; it is here: +http://people.cs.vt.edu/~gback/pintos/priority-donate-multiple-2.patch + +[...] + +I also wrote a test case for the second scenario: +http://people.cs.vt.edu/~gback/pintos/priority-donate-sema.c +http://people.cs.vt.edu/~gback/pintos/priority-donate-sema.ck + +I put the other tests up here: +http://people.cs.vt.edu/~gback/pintos/priority-donate-multiple2.c +http://people.cs.vt.edu/~gback/pintos/priority-donate-multiple2.ck + +From: "Godmar Back" +Subject: multiple threads waking up at same clock tick +To: "Ben Pfaff" +Date: Wed, 1 Mar 2006 08:14:47 -0500 + +Greg Benson points out another potential TODO item for P1. + +---- +One thing I recall: + +The alarm tests do not test to see if multiple threads are woken up if +their timers have expired. That is, students can write a solution +that just wakes up the first thread on the sleep queue rather than +check for additional threads. Of course, the next thread will be +woken up on the next tick. Also, this might be hard to test. + +--- +Way to test this: (from Godmar Back) + +Thread A with high priority spins until 'ticks' changes, then calls to +timer_sleep(X), Thread B with lower priority is then resumed, calls +set_priority to make its priority equal to that of thread A, then +calls timer_sleep(X), all of that before the next clock interrupt +arrives. + +On wakeup, each thread records wake-up time and calls yield +immediately, forcing the scheduler to switch to the other +equal-priority thread. Both wake-up times must be the same (and match +the planned wake-up time.) + +PS: +I actually tested it and it's hard to pass with the current ips setting. +The bounds on how quickly a thread would need to be able to return after +sleep appear too tight. Need another idea. From: "Godmar Back" @@ -134,12 +203,8 @@ Godmar Back writes: * Finish writing tour. -* Introduce a "yield" system call to speed up the syn-* tests. - via Godmar Back: -* Project 3 solution needs FS lock. - * Get rid of mmap syscall, add sbrk. * Make backtrace program accept multiple object file arguments, @@ -150,11 +215,6 @@ via Godmar Back: * Add FS persistence test(s). -* lock_acquire(), lock_release() don't need additional intr_dis/enable - calls, because the semaphore protects lock->holder. - - - * process_death test needs improvement * Internal tests. @@ -201,3 +261,66 @@ via Godmar Back: . opendir/readdir/closedir . everything needed for getcwd() + +To add partition support: + +- Find four partition types that are more or less unused and choose to + use them for Pintos. (This is implemented.) + +- Bootloader reads partition tables of all BIOS devices to find the + first that has the "Pintos kernel" partition type. (This is + implemented.) Ideally the bootloader would make sure there is + exactly one such partition, but I didn't implement that yet. + +- Bootloader reads kernel into memory at 1 MB using BIOS calls. (This + is implemented.) + +- Kernel arguments have to go into a separate sector because the + bootloader is otherwise too big to fit now? (I don't recall if I + did anything about this.) + +- Kernel at boot also scans partition tables of all the disks it can + find to find the ones with the four Pintos partition types (perhaps + not all exist). After that, it makes them available to the rest of + the kernel (and doesn't allow access to other devices, for safety). + +- "pintos" and "pintos-mkdisk" need to write a partition table to the + disks that they create. "pintos-mkdisk" will need to take a new + parameter specifying the type. (I might have partially implemented + this, don't remember.) + +- "pintos" should insist on finding a partition header on disks handed + to it, for safety. + +- Need some way for "pintos" to assemble multiple disks or partitions + into a single image that can be copied directly to a USB block + device. (I don't know whether I came up with a good solution yet or + not, or whether I implemented any of it.) + +To add USB support: + +- Needs to be able to scan PCI bus for UHCI controller. (I + implemented this partially.) + +- May want to be able to initialize USB controllers over CardBus + bridges. I don't know whether this requires additional work or if + it's useful enough to warrant extra work. (It's of special interest + for me because I have a laptop that only has USB via CardBus.) + +- There are many protocol layers involved: SCSI over USB-Mass Storage + over USB over UHCI over PCI. (I may be forgetting one.) I don't + know yet whether it's best to separate the layers or to merge (some + of) them. I think that a simple and clean organization should be a + priority. + +- VMware can likely be used for testing because it can expose host USB + devices as guest USB devices. This is safer and more convenient + than using real hardware for testing. + +- Should test with a variety of USB keychain devices because there + seems to be wide variation among them, especially in the SCSI + protocols they support. Should try to use a "lowest-common + denominator" SCSI protocol if any such thing really exists. + +- Might want to add a feature whereby kernel arguments can be given + interactively, rather than passed on-disk. Needs some though.