On Mon, Feb 27, 2017 at 01:28:28PM -0700, Andreas Dilger wrote: > On Feb 17, 2017, at 4:33 PM, Eric Biggers <ebiggers3@xxxxxxxxx> wrote: > > > > From: Eric Biggers <ebiggers@xxxxxxxxxx> > > > > When using both encryption and SELinux (or another feature that requires > > an xattr per file) on a filesystem with 256-byte inodes, each file's > > xattrs usually spill into an external xattr block. Currently, the > > xattrs are inherited in the order ACL, security, then encryption. > > Therefore, if spillage occurs, the encryption xattr will always end up > > in the external block. This is not ideal because the encryption xattrs > > contain a nonce, so they will always be unique and will prevent the > > external xattr blocks from being deduplicated. > > > > To improve the situation, change the inheritance order to encryption, > > ACL, then security. This gives the encryption xattr a better chance to > > be stored in-inode, allowing the other xattr(s) to be deduplicated. > > > > Note that it may be better for userspace to format the filesystem with > > 512-byte inodes in this case. However, it's not the default. > > > > Signed-off-by: Eric Biggers <ebiggers@xxxxxxxxxx> > > Reviewed-by: Andreas Dilger <adilger@xxxxxxxxx> > > Note that we've been using 512-byte xattrs for Lustre metadata servers > for ages. We may want to consider enabling this by default when the > filesystem features are set (e.g. crypto, inline data, etc). > > Having a general mechanism to bias xattrs to in-inode or external xattr > storage would be nice also, but I don't know any way to do this beyond > just having a list of xattr names and then prioritizing the ones that > go into the in-inode space. > I think it's a good idea to have mke2fs default to 512-byte inodes if '-O inline_data' is specified. But with '-O encrypt' it may be more debatable because there is no guarantee as to how many files userspace will actually choose to encrypt. It could be almost the whole filesystem, or just a few files, or even nothing at all. Regardless, I think adjusting the xattr inheritance order (as this patch does) has advantages but no real disadvantages, so it might as well be done too. Eric -- To unsubscribe from this list: send the line "unsubscribe linux-fscrypt" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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