Luu: Files are hard

Here is a lengthy postingfrom Dan Luu on why it is so hard to safely write files on Unix-likesystems. It comes down to a combination of POSIX semantics and filesystembugs. "Something to note here is that while btrfs's semantics aren'tinherently less reliable than ext3/ext4, many more applications corruptdata on top of btrfs because developers aren't used to coding againstfilesystems that allow directory operations to be reordered (ext2 was theonly other filesystem that allowed that reordering). We'll probably see asimilar level of bug exposure when people start using NVRAM drives thatonly have byte-level atomicity. People almost always just run some tests tosee if things work, rather than making sure they're coding against what'slegal in a POSIX filesystem."