linux-ext4 - Re: [PATCH v2 01/12] fs-verity: add a documentation file

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Date:   Mon, 17 Dec 2018 10:32:06 -0800
From:   Eric Biggers <ebiggers@...nel.org>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     linux-fscrypt@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-ext4@...r.kernel.org, linux-f2fs-devel@...ts.sourceforge.net,
        linux-integrity@...r.kernel.org, linux-kernel@...r.kernel.org,
        "Theodore Y . Ts'o" <tytso@....edu>,
        Jaegeuk Kim <jaegeuk@...nel.org>,
        Victor Hsieh <victorhsieh@...gle.com>,
        Chandan Rajendra <chandan@...ux.vnet.ibm.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH v2 01/12] fs-verity: add a documentation file

On Mon, Dec 17, 2018 at 08:49:49AM -0800, Christoph Hellwig wrote:
> 
> > > Given that you alread use an ioctl as the interface what is the problem
> > > of passing this data through the ioctl?
> > 
> > Do you mean pass the verity metadata in a buffer?  That cannot work in general,
> > because it may be too large to fit into memory.
> 
> Have a pointer in the ioctl and do get_user_pages on it.

I don't see how that helps.  The Merkle tree can still be too large to fit in
memory.  In the worst case, it might not even fit in the address space.  And I
don't see how get_user_pages() helps either over just copy_from_user(); what are
you proposing to do with the pages after getting them, exactly?

- Eric