Re: [LSF/MM/BPF TOPIC] Dropping page cache of individual fs

[Matthew Wilcox <willy@infradead.org>]

On Wed, Jan 17, 2024 at 03:35:28PM +0100, Jan Kara wrote:
> OK. So could we then define the effect of your desired call as calling
> posix_fadvise(..., POSIX_FADV_DONTNEED) for every file? This is kind of
> best-effort eviction which is reasonably well understood by everybody.

I feel like we're in an XY trap [1].  What Christian actually wants is
to not be able to access the contents of a file while the device it's
on is suspended, and we've gone from there to "must drop the page cache".

We have numerous ways to intercept file reads and make them either
block or fail.  The obvious one to me is security_file_permission()
called from rw_verify_area().  Can we do everything we need with an LSM?

[1] https://meta.stackexchange.com/questions/66377/what-is-the-xy-problem