One more
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Frans Kaashoek
parent
e627608810
commit
26ce97fc76
123
Notes
123
Notes
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bochs 2.2.6:
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./configure --enable-smp --enable-disasm --enable-debugger --enable-all-optimizations --enable-4meg-pages --enable-global-pages --enable-pae --disable-reset-on-triple-fault
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bochs CVS after 2.2.6:
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./configure --enable-smp --enable-disasm --enable-debugger --enable-all-optimizations --enable-4meg-pages --enable-global-pages --enable-pae
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bootmain.c doesn't work right if the ELF sections aren't
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sector-aligned. so you can't use ld -N. and the sections may also need
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to be non-zero length, only really matters for tiny "kernels".
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kernel loaded at 1 megabyte. stack same place that bootasm.S left it.
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kinit() should find real mem size
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and rescue useable memory below 1 meg
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no paging, no use of page table hardware, just segments
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no user area: no magic kernel stack mapping
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so no copying of kernel stack during fork
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though there is a kernel stack page for each process
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no kernel malloc(), just kalloc() for user core
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user pointers aren't valid in the kernel
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are interrupts turned on in the kernel? yes.
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pass curproc explicitly, or implicit from cpu #?
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e.g. argument to newproc()?
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hmm, you need a global curproc[cpu] for trap() &c
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no stack expansion
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test running out of memory, process slots
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we can't really use a separate stack segment, since stack addresses
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need to work correctly as ordinary pointers. the same may be true of
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data vs text. how can we have a gap between data and stack, so that
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both can grow, without committing 4GB of physical memory? does this
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mean we need paging?
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perhaps have fixed-size stack, put it in the data segment?
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oops, if kernel stack is in contiguous user phys mem, then moving
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users' memory (e.g. to expand it) will wreck any pointers into the
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kernel stack.
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do we need to set fs and gs? so user processes can't abuse them?
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setupsegs() may modify current segment table, is that legal?
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trap() ought to lgdt on return, since currently only done in swtch()
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protect hardware interrupt vectors from user INT instructions?
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test out-of-fd cases for creating pipe.
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test pipe reader closes then write
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test two readers, two writers.
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test children being inherited by grandparent &c
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some sleep()s should be interruptible by kill()
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locks
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init_lock
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sequences CPU startup
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proc_table_lock
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also protects next_pid
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per-fd lock *just* protects count read-modify-write
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also maybe freeness?
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memory allocator
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printf
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in general, the table locks protect both free-ness and
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public variables of table elements
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in many cases you can use table elements w/o a lock
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e.g. if you are the process, or you are using an fd
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lock order
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per-pipe lock
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proc_table_lock fd_table_lock kalloc_lock
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console_lock
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do you have to be holding the mutex in order to call wakeup()? yes
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device interrupts don't clear FL_IF
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so a recursive timer interrupt is possible
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what does inode->busy mean?
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might be held across disk reads
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no-one is allowed to do anything to the inode
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protected by inode_table_lock
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inode->count counts in-memory pointers to the struct
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prevents inode[] element from being re-used
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protected by inode_table_lock
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blocks and inodes have ad-hoc sleep-locks
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provide a single mechanism?
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kalloc() can return 0; do callers handle this right?
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test: one process unlinks a file while another links to it
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test: one process opens a file while another deletes it
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test: deadlock d/.. vs ../d, two processes.
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test: dup() shared fd->off
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test: does echo foo > x truncate x?
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sh: ioredirection incorrect now we have pipes
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sh: chain of pipes won't work, also ugly that parent closes fdarray entries too
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sh: dynamic memory allocation?
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sh: should sh support ; () &
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sh: stop stdin on ctrl-d (for cat > y)
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really should have bdwrite() for file content
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and make some inode updates async
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so soft updates make sense
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disk scheduling
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echo foo > bar should truncate bar
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so O_CREATE should not truncate
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but O_TRUNC should
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make it work on a real machine
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release before acquire at end of sleep?
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check 2nd disk (i.e. if not in .bochsrc)
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