logwrapper: open child_ptty in child process and remove ignore_int_quit

Opening child_ptty before fork() means that the parent process will
use child_ptty as the controlling terminal if it doesn't already have
one.  This is a problem, because when the parent_ptty closes, SIGHUP
will be sent to the parent process, since its controlling terminal has
closed.

It's better to have the child process start its own session and then
open child_ptty as its controlling terminal.  In this case, the child
process will get SIGHUP if the parent process exits, but the parent
process avoids the original issue.

There is a concern that the child_ptty will never be opened and
POLLHUP will never be generated, but there is a work-around in place
with a timeout to handle that extremely rare situation.

Secondly, remove the ignore_int_quit logic.  It is described to
totally ignore these signals, similar to `nohup` which should be
preferred.  However, it regressed shortly after being introduced in
2013 and serves essentially no purpose currently.

Thirdly, add a forward_signals option that does what we should have
done the whole time with signals: it forwards SIGHUP, SIGQUIT, and
SIGINT to the child process and let that process handle them.  This
only needs to be enabled in the `logwrapper` case itself.  Other
processes should not need to change any signals.  This fixes case 3)
below.

Lastly, add O_CLOEXEC where appropriate.

Test: launch process as `adb shell logwrapper yes`
      1) The both processes exit when given SIGINT
      2) The process prints when abbreviated is not enabled
      3) The process does print when abbreviated is enabled;
         this was previously broken
Test: launch process as `adb shell` then `logwrapper yes`
      4) The both processes exit when given SIGINT
      5) The process prints if abbreviated is enabled or not.
      6) Ctrl-c then Ctrl-c again rapidly and observe that the
         logwrapper process is terminated by the second Ctrl-c.
Test: simulate a failure in child() before opening child_tty and
      observe logwrapper and the child exiting appropriately.

Change-Id: Ia76cd17e16535500170d8f5e2183b3bbbf843df7

0 files changed, 0 insertions, 0 deletions