On Thu, Jun 12, 2014 at 09:36:49PM -0500, Eric Sandeen wrote: > On 6/12/14, 9:14 PM, JP Abgrall wrote: > > This provides an interface for issuing secure trims to parallel > > the existing interface for non-secure trim. > > Which does what? A bit of digging through git history tells > me, but an idiot reader like myself doesn't know what a > "secure trim" is. ;) Would be nice to have that info, > and the reason for elevating it from a block-level ioctl > to an fs-level ioctl in the commit log. > > IOWS: your commit log says what, but not why. "Secure discard" is only "secure" if every discard that is issued is secure. Filesystems optimise away repeated discards for freed regions, so FITRIM followed by SFITRIM means the regions trimmed by the initial FITRIM are not securely erased from the underlying media, and you can't get then to be securely erased until <hand-wave> stuff happens. Indeed, mixing -o discard and SFITRIM is a recipe for confusion and leakage - "but I used secure trim on the device!" - and so all discards either have to be secure or not. Further, some filesystems may other copies of stale data in the discarded ranges (e.g. data from unlinked files in the journal or even in unused portions of metadata blocks), so you can't really say that secure TRIM provides any sort of security against leakage at the filesystem layer... Hence I think secure discard should be a block layer property and controlled at that layer rather than giving an incorrect impression that FITRIM provides protection against unintentional data leakage from the filesystem.... Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
