[PATCH] proc: refactor reading directories of tasks

[PATCH] proc: refactor reading directories of tasks

There are a couple of problems this patch addresses.
- /proc/<tgid>/task currently does not work correctly if you stop reading
  in the middle of a directory.

- /proc/ currently requires a full pass through the task list with
  the tasklist lock held, to determine there are no more processes to read.

- The hand rolled integer to string conversion does not properly running
  out of buffer space.

- We seem to be batching reading of pids from the tasklist without reason,
  and complicating the logic of the code.

This patch addresses that by changing how tasks are processed.  A
first_<task_type> function is built that handles restarts, and a
next_<task_type> function is built that just advances to the next task.

first_<task_type> when it detects a restart usually uses find_task_by_pid.  If
that doesn't work because there has been a seek on the directory, or we have
already given a complete directory listing, it first checks the number tasks
of that type, and only if we are under that count does it walk through all of
the tasks to find the one we are interested in.

The code that fills in the directory is simpler because there is only a single
for loop.

The hand rolled integer to string conversion is replaced by snprintf which
should handle the the out of buffer case correctly.

Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>