Remove the Notes file.

789a5877 · Silas Boyd-Wickizer · 006f8758 · 006f8758
--- a/Notes
+++ b/Notes
-bochs 2.2.6:
-./configure --enable-smp --enable-disasm --enable-debugger --enable-all-optimizations --enable-4meg-pages --enable-global-pages --enable-pae --disable-reset-on-triple-fault
-bochs CVS after 2.2.6:
-./configure --enable-smp --enable-disasm --enable-debugger --enable-all-optimizations --enable-4meg-pages --enable-global-pages --enable-pae 
-
-bootmain.c doesn't work right if the ELF sections aren't
-sector-aligned. so you can't use ld -N. and the sections may also need
-to be non-zero length, only really matters for tiny "kernels".
-
-kernel loaded at 1 megabyte. stack same place that bootasm.S left it.
-
-kinit() should find real mem size
-  and rescue useable memory below 1 meg
-
-no paging, no use of page table hardware, just segments
-
-no user area: no magic kernel stack mapping
-  so no copying of kernel stack during fork
-  though there is a kernel stack page for each process
-
-no kernel malloc(), just kalloc() for user core
-
-user pointers aren't valid in the kernel
-
-are interrupts turned on in the kernel? yes.
-
-pass curproc explicitly, or implicit from cpu #?
-  e.g. argument to newproc()?
-  hmm, you need a global curproc[cpu] for trap() &c
-
-no stack expansion
-
-test running out of memory, process slots
-
-we can't really use a separate stack segment, since stack addresses
-need to work correctly as ordinary pointers. the same may be true of
-data vs text. how can we have a gap between data and stack, so that
-both can grow, without committing 4GB of physical memory? does this
-mean we need paging?
-
-perhaps have fixed-size stack, put it in the data segment?
-
-oops, if kernel stack is in contiguous user phys mem, then moving
-users' memory (e.g. to expand it) will wreck any pointers into the
-kernel stack.
-
-do we need to set fs and gs? so user processes can't abuse them?
-
-setupsegs() may modify current segment table, is that legal?
-
-trap() ought to lgdt on return, since currently only done in swtch()
-
-protect hardware interrupt vectors from user INT instructions?
-
-test out-of-fd cases for creating pipe.
-test pipe reader closes then write
-test two readers, two writers.
-test children being inherited by grandparent &c
-
-some sleep()s should be interruptible by kill()
-
-locks
-  init_lock
-    sequences CPU startup
-  proc_table_lock
-    also protects next_pid
-  per-fd lock *just* protects count read-modify-write
-    also maybe freeness?
-  memory allocator
-  printf
-
-in general, the table locks protect both free-ness and
-  public variables of table elements
-  in many cases you can use table elements w/o a lock
-  e.g. if you are the process, or you are using an fd
-
-lock order
-  per-pipe lock
-  proc_table_lock fd_table_lock kalloc_lock
-  console_lock
-
-do you have to be holding the mutex in order to call wakeup()? yes
-
-device interrupts don't clear FL_IF
-  so a recursive timer interrupt is possible
-
-what does inode->busy mean?
-  might be held across disk reads
-  no-one is allowed to do anything to the inode
-  protected by inode_table_lock
-inode->count counts in-memory pointers to the struct
-  prevents inode[] element from being re-used
-  protected by inode_table_lock
-
-blocks and inodes have ad-hoc sleep-locks
-  provide a single mechanism?
-
-kalloc() can return 0; do callers handle this right?
-
-test: one process unlinks a file while another links to it
-test: one process opens a file while another deletes it
-test: deadlock d/.. vs ../d, two processes.
-test: dup() shared fd->off
-test: does echo foo > x truncate x?
-
-sh: ioredirection incorrect now we have pipes
-sh: chain of pipes won't work, also ugly that parent closes fdarray entries too
-sh: dynamic memory allocation?
-sh: should sh support ; () &
-sh: stop stdin on ctrl-d (for cat > y)
-
-really should have bdwrite() for file content
-  and make some inode updates async
-  so soft updates make sense
-
-disk scheduling
-echo foo > bar should truncate bar
-  so O_CREATE should not truncate
-  but O_TRUNC should
-
-make it work on a real machine
-release before acquire at end of sleep?
-check 2nd disk (i.e. if not in .bochsrc)