[PATCH v6 4/6] ima: use fs method to read integrity data

On Mon, 2017-08-28 at 05:13 +0100, Al Viro wrote:

On Tue, Aug 15, 2017 at 10:43:55AM -0400, Mimi Zohar wrote:

quoted

From: Christoph Hellwig <hch@lst.de>

Add a new ->integrity_read file operation to read data for integrity
hash collection.  This is defined to be equivalent to ->read_iter,
except that it will be called with the i_rwsem held exclusively.

Hmm...  I'm really tempted to add default_integrity_read() that would
just call ->read_iter(), with boilerplate part becoming
	.integrity_read = default_integrity_read

How can it automatically call the fs read_iter() without knowing if
the fs read_iter() takes the i_rwsem? ?Or are you suggesting that the
default_integrity_read is defined as generic_file_read_iter()?

Mimi

Note that all stuff accessed in it would be fresh in caches, so
it's not as if we had serious overhead there.  And we are going
to be reading from file, anyway...

I agree that it should be an opt-in from filesystem; default is still
"don't know how to read, sod off".  It's just that telling at the
glance whether it's supposed to be a simple case or something tricky
is needed would be simpler that way and it might turn out to be
more robust that way...
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