On Fri, Jul 26, 2013 at 09:20:34AM -0400, Jörn Engel wrote: > On Fri, 26 July 2013 12:01:23 +0400, Vyacheslav Dubeyko wrote: > > > > We are discussing not about good or bad idea. We need to elaborate a > > right solution. I think that suggested idea is not clear. Do you > > want to support compression in ext4? Or do you want to add some new > > compression feature (likewise file-oriented compression)? If we are > > talking about compression in ext4 then it needs to use e2compr patch > > set. Otherwise, if we are talking about file compression then it is > > not question of concrete filesystem. And we need to make > > implementation on VFS level. It is only architectural point of view. > > I don't think the e2compr patches are strictly necessary. They are a > good option, but not the only one. > > One trick to simplify the problem is to make Dhaval's compressed files > strictly read-only. It will require some dance to load the compressed > content, flip the switch, then uncompress data on the fly and disallow > writes. Not the most pleasing of interfaces, but yet another option. > > > Why do you try to implement likewise concept on kernel level? It > > looks like you try to move some user-space concept in kernel-space. > > The kernel controls the page cache. Once the page cache is filled > with uncompressed file content, you can do mmap, regular file io, etc. > Putting uncompression code into the kernel makes sense to me. Whether > a solution different from e2compr makes sense is yet to be seen. > > Whatever you do, it will require support from the on-disk format and > the userspace ABI. Setting the compression bit on a file has the > clear advantage that it is an established interface and also supported > by other filesystems. Introducing yet another interface requires a > fairly strong case to be made. But who knows, maybe Dhaval can pull > it off. Come to think of it, the whole thing could be handled entirely in user space through fuse. While this is probably a workable solution on desktop/server environments, it doesn't pan out on Android: /dev/fuse is rarely available, and even if it were, fusermount needs to be there and be a setuid program (or have the right capabilities). So, another angle could be to allow some things to happen without privileges, such as mounting filesystems in a private namespace. That wouldn't solve the lack of /dev/fuse, though. Mike -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
