linux-ext4 - Re: [PATCH 3/4] f2fs: add inline encryption support

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Date:   Thu, 18 Jun 2020 11:13:57 -0700
From:   Eric Biggers <ebiggers@...nel.org>
To:     Chao Yu <yuchao0@...wei.com>
Cc:     Satya Tangirala <satyat@...gle.com>, linux-fscrypt@...r.kernel.org,
        linux-fsdevel@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net, linux-ext4@...r.kernel.org
Subject: Re: [PATCH 3/4] f2fs: add inline encryption support

Hi Chao,

On Thu, Jun 18, 2020 at 06:06:02PM +0800, Chao Yu wrote:
> > @@ -936,8 +972,11 @@ void f2fs_submit_page_write(struct f2fs_io_info *fio)
> >  
> >  	inc_page_count(sbi, WB_DATA_TYPE(bio_page));
> >  
> > -	if (io->bio && !io_is_mergeable(sbi, io->bio, io, fio,
> > -			io->last_block_in_bio, fio->new_blkaddr))
> > +	if (io->bio &&
> > +	    (!io_is_mergeable(sbi, io->bio, io, fio, io->last_block_in_bio,
> > +			      fio->new_blkaddr) ||
> > +	     !f2fs_crypt_mergeable_bio(io->bio, fio->page->mapping->host,
> > +				       fio->page->index, fio)))
> 
> bio_page->index, fio)))
> 
> >  		__submit_merged_bio(io);
> >  alloc_new:
> >  	if (io->bio == NULL) {
> > @@ -949,6 +988,8 @@ void f2fs_submit_page_write(struct f2fs_io_info *fio)
> >  			goto skip;
> >  		}
> >  		io->bio = __bio_alloc(fio, BIO_MAX_PAGES);
> > +		f2fs_set_bio_crypt_ctx(io->bio, fio->page->mapping->host,
> > +				       fio->page->index, fio, GFP_NOIO);
> 
> bio_page->index, fio, GFP_NOIO);
> 

We're using ->mapping->host and ->index.  Ordinarily that would mean the page
needs to be a pagecache page.  But bio_page can also be a compressed page or a
bounce page containing fs-layer encrypted contents.

Is your suggestion to keep using fio->page->mapping->host (since encrypted pages
don't have a mapping), but start using bio_page->index (since f2fs apparently
*does* set ->index for compressed pages, and if the file uses fs-layer
encryption then f2fs_set_bio_crypt_ctx() won't use the index anyway)?

Does this mean the code is currently broken for compression + inline encryption
because it's using the wrong ->index?  I think the answer is no, since
f2fs_write_compressed_pages() will still pass the first 'nr_cpages' pagecache
pages along with the compressed pages.  In that case, your suggestion would be a
cleanup rather than a fix?

It would be helpful if there was an f2fs mount option to auto-enable compression
on all files (similar to how test_dummy_encryption auto-enables encryption on
all files) so that it could be tested more easily.

- Eric