Hi Chandan, On Wed, Feb 21, 2018 at 03:27:34PM +0530, Chandan Rajendra wrote: > On Wednesday, February 21, 2018 6:18:21 AM IST Eric Biggers wrote: > > Hi Chandan, > > > > On Mon, Feb 12, 2018 at 03:13:36PM +0530, Chandan Rajendra wrote: > > > This patchset implements code to support encryption of Ext4 filesystem > > > instances that have blocksize less than pagesize. The patchset has > > > been tested on both ppc64 and x86_64 machines. > > > > > > Eric, fscrypt_mpage_readpages() (originally, ext4_mpage_readpages()) > > > still retains the ability to read non-encrypted file data. Please let > > > me know if the code has to be changed such that > > > fscrypt_mpage_readpages() makes it mandatory for the file's data to be > > > encrypted. > > > > > > TODO: > > > F2FS and UBIFS code needs to be updated to make use of the newly added > > > fscrypt functions. I will do that in the next version of the patchset. > > > > > > Changelog: > > > "RFC V1" -> "RFC V2": > > > 1. Ext4's "encryption aware" functionality in fs/ext4/readpage.c has > > > been moved to fs/crypto/. > > > 2. fscrypt functions have now been renamed to indicate that they work > > > on blocks rather than pages. > > > Eric, I have renamed completion_pages() to fscrypt_complete_pages() > > > rather than to fscrypt_complete_blocks(). This is because we have a > > > new function fscrypt_complete_block() (which operates on a single > > > block) and IMHO having the identifier fscrypt_complete_blocks() > > > which differs from it by just one letter would confuse the reader. > > > 3. ext4_block_write_begin() now clears BH_Uptodate flag when > > > decryption of boundary blocks fail. > > > 4. fscrypt_encrypt_page() (now renamed to fscrypt_encrypt_block()) is > > > now split into two functions. fscrypt_prep_ciphertext_page() > > > allocates and initializes the fscrypt context and the bounce > > > page. fscrypt_encrypt_block() is limited to encrypting the > > > filesystem's block. > > > 5. fscrypt_zeroout_range() has been updated to work on blocksize < > > > pagesize scenario. > > > 6. Documentation/filesystems/fscrypt.rst has been updated to indicate > > > encryption support for blocksize < pagesize. > > > > > > Thanks to Eric Biggers for providing review comments for "RFC V1". > > > > > > > Thanks for the new version of the patchset. > > > > I see you decided to move ext4's readpages to fs/crypto/. Did you also consider > > the other alternatives I had suggested, such as adding an encryption callback to > > the generic mpage_readpages(), or making fscrypt non-modular and then calling it > > directly from mpage_readpages()? Maybe you did, but I don't see the tradeoffs > > addressed in the patchset at all. The patches need to explain *why* you're > > doing what you're doing, not just *what* you're doing. > > I had glanced through F2FS and UBIFS source code. F2FS has its own version of > mpage_readpage[s] and UBIFS does not use mpage_readpage[s] > functionality. This was the major reason for deciding to not go with the > approach of having a decryption call back passed to mpage_readpage[s]. > > Apart from the reason of memory being wasted on systems which do not require > files to be encrypted, the previously listed reason of mpage_readpage[s] not > being used by F2FS and UBIFS also played a role is deciding against invoking > fscrypt_decrypt_bio_blocks() from within mpage_readpages(). > Sure, F2FS and UBIFS don't use mpage_readpages(), block_write_full_page(), or __block_write_begin(). But that doesn't mean it's a good idea to copy and paste all of those functions from generic code to fs/crypto or to fs/ext4 just to add encryption support. It will be difficult to maintain two copies of the code. The other option I suggested, which I think you still haven't addressed at all, is adding an encryption/decryption callback to those functions, which would be provided by the filesystem. See for example how __block_write_begin_int() takes in an optional 'struct iomap *' pointer; maybe we could do something similar with crypto? Note, that approach would have the advantage of not requiring that fscrypt be built-in. Just a thought, I haven't tried writing the code yet to see how difficult/ugly it would be... Eric
