with procfs's cmdline - from the PR:
The cmdline implementation in procfs is bogus. It's possible that
part of the fix is a workaround of a UVM problem - that is, when
(internally) accessing the top of the process VM (the end of the
args) a request for I/0 of a PAGE_SIZE'd block starting at less
than a PAGE_SIZE from the end of the mem space returns EINVAL
rather than the data that is available. Whether this is a bug
in UVM or not depends upon how it is defined to work, and I was
unable to determine that. (Simon Burge found that problem, and
provided the basis of the workaround/fix).
Then, the cmdline function is unable to read more than one
page of args, and a good thing too, as the way it is written
attempting to get more than that would reference into lala land.
And, on an attempt to read a lot of data when the above is
fixed, most of the data won't be returned, only the final block
of any read.
Tested on alpha, pmax, i386 and sparc.
and PID allocation MP-safe. A new process state is added: SDEAD. This
state indicates that a process is dead, but not yet a zombie (has not
yet been processed by the process reaper).
SDEAD processes exist on both the zombproc list (via p_list) and deadproc
(via p_hash; the proc has been removed from the pidhash earlier in the exit
path). When the reaper deals with a process, it changes the state to
SZOMB, so that wait4 can process it.
Add a P_ZOMBIE() macro, which treats a proc in SZOMB or SDEAD as a zombie,
and update various parts of the kernel to reflect the new state.
array of ARG_MAX size. ARG_MAX is currently 256k, which causes a rather
serious stack overflow (kernel stacks are not very large, usually 8k).
Fixes memory corruption problems observed after accessig /proc/1/cmdline
during tests. Problem in my case manifested itself as massive lossage
in ffs_sync(), resulting in a crash, and sometimes, pooched file systems.
XXX This could, and probably should, be rewritten to use a much smaller
temporary buffer, and a loop around uiomove().
- Don't error out on P_SYSTEM or SZOMB processes; instead, do what ps(1)
would do, i.e. the p_comm in parenthesis.
- Use uvm_io() (or procfs_rwmem() if !UVM) to read the target process's
psstrings and argument vector. Using copyin() is problematic, because
it operates on the current processes! That is, the old code would
always get the `cmdline' of the process reading the file, not that of
the target process.
simonb