On Wed, Jul 12, 2017 at 07:17:37PM -0400, Theodore Ts'o wrote: > On Wed, Jul 12, 2017 at 06:07:11PM +0100, Richard W.M. Jones wrote: > > > > https://bugzilla.redhat.com/show_bug.cgi?id=1470157 > > > > To cut a long story short, we were using libext2fs to create > > filesystems where short symlinks (< 60 bytes) were stored the same way > > as long symlinks, ie. stored as an ordinary file instead of being > > stored in the inode. > > > > I think the reason we were creating filesystems wrongly in the first > > place is because our code has been around since about 2008, and the > > nice ext2fs_symlink function that deals properly with fast/slow > > symlinks wasn't added until 2013. > > Thanks for the report. I had been hesitant about making this change > (and had been pushing back from those who were advocating for this > change) precisely because I was afraid that this might be a situation. > > What convinced me to accept the change is that (a) I had scanned all > of the old kernels and old versions of e2fsprogs and convinced myself > that aside from someone manually creating symlinks using low-level > libext2fs, symlinks < 60 bytes would never be stored in external > blocks, and (b) using the i_blocks logic to determine whether or not > we had a slow link was getting really painful. > > > It's not too much trouble for us to recreate the incorrect > > filesystems. Mostly we're creating one-off throwaway filesystems for > > appliances anyway and they don't live for long. > > > > But I suppose this might be a warning that other incorrect filesystems > > exist which will break with Linux >= 4.13. > > So I see this is going to break libvert and libguestfs. So people who > are running existing distribution userspaces and then upgrade to 4.13 > will break. > > Hmm... I suppose we could add back support to let the kernel to use > the i_blocks logic if the ea_inode feature is not enabled. E2fsck > would still complain so we can try to gradually force userspace to do > things "correctly", but at least we would be backwards compatible. > > Comments? >From my point of view it's not too much trouble to recreate these filesystems, and we've already proposed a fix for supermin so it creates symlinks properly[1]. I think it might be a good idea to get e2fsck to complain about these filesystems though. It'll at least tell you how widespread (or otherwise) the problem might be. Rich. [1] https://www.redhat.com/archives/libguestfs/2017-July/msg00084.html -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones Read my programming and virtualization blog: http://rwmj.wordpress.com libguestfs lets you edit virtual machines. Supports shell scripting, bindings from many languages. http://libguestfs.org
