Re: [RFC][PATCH 1/4][cr]: Add uid, euid params to f_modown()

[Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>]

Jamie Lokier [jamie@shareable.org] wrote:
| Sukadev Bhattiprolu wrote:
| > Checkpoint/restart of file-owner.
| > 
| > Add uid, euid parameters to f_modown(). These parameters will be needed
| > when restarting an application (and hence restoring the file information),
| > from a checkpoint image.
| 
| This is used to make sure I/O signals on sockets, ttys, devices and so
| on are delivered to a particular process.

Good point.
| 
| If any of those signals are lost when an event happens around the same

Well, signals are not lost across C/R - if they were pending at
checkpoint, they will be pending on restart.

| time as c/r (for example, more data arriving on a pipe, a device
| becomes readable/writable, or room becoming available to write, or
| urgent data on a socket), a process depending on it can get stuck -
| unless the process knows that c/r happened, so it knows to call
| select() on all those fds after the c/r.

Real devices like ttys are still TBD from C/R perspective - so data
arriving from the tty is still a problem. Applications using such
devices cannot be checkpointed.

But for pipes, (and sockets ?) we expect that both ends are checkpointed
as a container. So before the container is frozen for checkpoint, either
both the write() and SIGIO (due to new data on the pipe) both happen or
neither.


Sukadev