Hi Ted, Please ignore the following email, Eric has replied to me. :) I need to dig into these fs-verity patches later and best wishes to fs-verity. Thanks, Gao Xiang On 2018/8/25 15:33, Gao Xiang wrote: > Hi Ted, > > Thanks for your detailed reply. Sorry about my english, the words could not be logical. > > Tiny pieces in B-tree to compose a page is too far from us too, and you are right, > fs-verity is complete for >99% cases for the existed file system, and no need to worry about currently. > > As I mentioned in reply to Eric, I am actually curious about the Google fs-verity roadmap > for the future Android, I need to analyze if it is only limited to APKs for the read-write partitions > and not to replace dm-verity in the near future since fs-verity has some conflicts > to EROFS I am working on I mentioned in the email to Eric. > > I think it is more than just to handle FILE_MAPPING and bio-strict for compression use. > > On 2018/8/25 13:06, Theodore Y. Ts'o wrote: >> But I'd suggest worrying about it when such a file system >> comes out of the woodwork, and someone is willing to do the work to >> integrate fserity in that file system. >> > Yes, we are now handling partial page due to compression use. > > fs could submit bios in pages from different mapping(FILE_MAPPING[compress in-place and no caching > compressed page to reduce extra memory overhead] or META_MAPPING [for caching compressed page]) and > they could be decompressed into many full pages and (possible) a partial page (in-place or out-of-place). > > so in principle, since we have BIO_MAX_PAGES limitation, a filemap page could be Uptodate > after two bios is ended and decompressed. and other runtime limitations could also divide a bio into two bios for encoded cases. > > Therefore, I think in that case we could not just consider FILE_MAPPING and one bio, and as you said `In > that case, it could call fsverity after assembling the page in the page cache.' should be done in this way. > >> Well, the userspace interface for instantiating a fs-verity file is >> that it writes the file data with the fs-verity metadata (which >> consists of the Merkle tree with a fs-verity header at the end of the >> file). The program (which might be a package manager such as dpkg or >> rpm) would then call an ioctl which would cause the file system to >> read the fs-verity header and make only the file data visible, and the >> file system would the verify the data as it is read into the page >> cache. > Thanks for your reply again, I think fs-verity is good enough for now. > However, I need to think over about fs-verity itself more... :( > > Thanks, > Gao Xiang
