On Fri, Apr 22, 2022 at 11:01 PM Seth Arnold <seth.arn...@canonical.com> wrote:
>
> On Fri, Apr 22, 2022 at 09:58:14AM -0700, Bryce Harrington wrote:
> > LP page: https://launchpad.net/ubuntu/+source/pv
>
> > Or other considerations that need made before deciding?
>
> pv is popular in the OpenZFS communities for use with zfs send | zfs recv
> -- as is mbuffer, which exists more to provide much larger buffering than
> the usual libc stdio buffers. mbuffer doesn't have progress bars, but does
> show throughput:
>
> $ dd if=/dev/urandom | mbuffer > /dev/null
> in @ 32.5 MiB/s, out @ 32.5 MiB/s, 166 MiB total, buffer 0% full^C
> 341133+0 records in
> 341133+0 records out
> 174660096 bytes (175 MB, 167 MiB) copied, 5.13954 s, 34.0 MB/s
> mbuffer: warning: error during output to <stdout>: canceled
> summary: 167 MiByte in 5.1sec - average of 32.4 MiB/s
>
> One feature of pv that slightly worries me is that you can change the
> parameters of an already-running instance by running it again, with -R:
>
> -R PID, --remote PID
> If PID is an instance of pv that is already running,
> -R PID will cause that instance to act as though it
> had been given this instance's command line instead.
> For example, if pv -L 123K is running with process ID
> 9876, then running pv -R 9876 -L 321K will cause it to
> start using a rate limit of 321KiB instead of 123KiB.
> Note that some options cannot be changed while
> running, such as -c, -l, -f, -D, -E, and -S.
>
> It's probably fine. (Afterall, it's possible to disable the yama sysctl
> kernel.yama.ptrace_scope and attach a debugger to the process to modify
> whatever you want.) But it's also possible it's not fine.
Hi Seth,
thanks for raising this, but I'd like to understand where in
between "just raising an eyebrow" and "total blocker" this really is.
The option only allows you to change those which are sane to change.
And it is part of user-access control, you can't IPC an instance you have no
control of e.g. a normal user can't change other users pv process.
user -> root:
pv: 498786: Operation not permitted
To some extent I consider this nothing more than an advanced version of
DD having SIGUSR1 to report progress output - and that never was a problem.
I wonder, is everything with an IPC msgqeue a problem or is there something
here that I do not yet see that makes this more affected?
Could you outline what level of concern you have here - see the starting
quote of "just raising an eyebrow" and "total blocker" .
And if it is important - would trying to create any of the following
help a lot to overcome your concerns?:
a) something like the apparmor profile Thomas suggested?
b) an opt-out option like "--no-remote - do not create IPC
msgqueue for later change of arguments"
c) it was just a hint and would not be a blocker
> Thanks
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--
Christian Ehrhardt
Staff Engineer, Ubuntu Server
Canonical Ltd
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