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Date: Tue, 17 Apr 2018 15:23:30 +0100
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To: Dmitry Stogov <dmitry@zend.com>
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Subject: FPM preloading of PHP files
From: bukka@php.net (Jakub Zelenka)

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Hi Dmitry,

This is a bit different topic to FFI discussion so creating a new thread.
You wrote this in the FFI extension discussion:

At the same time, we will develop a technology to preload and reuse  PHP
> files across requests.
> And allow FFI there.


Have you been thinking about it in the FPM context? I'm asking as I have
been pondering with a related idea about some restructuring how things work
currently in the FPM. I will try to give a quick overview of the current
way how things work (for those who read this and are not familiar with it),
the problem that it is already causing and finally the idea that I have. :)

The thing is that at the moment there is just a master process that except
other things does the module init and spawns children. Each child is then
configured by the pool configuration which means that it can have a
different effective user id. It's simple and it works in most cases.
However there is an issue if it tries to access shared resources in other
pools running under different user which can happen due to the fact that
the initialization is done during MINIT by master (root user in such
case).  One example is the opcache that tries to kill lockers as described
in https://bugs.php.net/bug.php?id=74709 . I think that it's also not ideal
to do MINIT as a root from security point of view (the last security issue
is actually good example of that - https://bugs.php.net/bug.php?id=75605 ).
However not sure if there are some extension that depends on it.

As you can imagine, it would get even worse if you allow preloading of PHP
script in master so such implementation would be a no-go IMHO.

What I have been thinking about is to have a new process (I will call it a
pool manager) for each pool that would except other things spawn and manage
children and run under the same user. It would also do the MINIT and it
could possibly preload PHP files and load the libraries for FFI
(considering there would be a support in the engine for that - some kind of
partial execution or whatever you think would be best). Master would then
spawn and manage the pool managers as well as doing other things like log
handling. That would prevent the user mix up mentioned above - in the
example case, the opcache would have separate shared memory for each pool.

WDYT?

Cheers

Jakub

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