From: Christoph Hellwig

Sent: 27 August 2020 16:00

Don't allow calling ->read or ->write with set_fs as a preparation for
killing off set_fs.  All the instances that we use kernel_read/write on
are using the iter ops already.

If a file has both the regular ->read/->write methods and the iter
variants those could have different semantics for messed up enough
drivers.  Also fails the kernel access to them in that case.

Is there a real justification for that?
For system calls supplying both methods makes sense to avoid
the extra code paths for a simple read/write.

Any one stupid enough to make them behave differently gets
what they deserve.

	David

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