* Andreas Dilger: > On Sep 06, 2009 13:39 +0000, Florian Weimer wrote: >> The FIBMAP ioctl requires CAP_SYS_RAWIO, but FIEMAP doesn't. Why's >> that? Is it that there is no backwards-compatible way to introduce >> locking on the bmap path? > > I'm not sure why there is a root-only requirement for FIBMAP, but the > FIEMAP data is definitely useful even for non-root users for many > reasons, such as optimized file copies/rsync/tar/etc skipping holes > in sparse files easily. I'm slightly worried because the generic FIEMAP-on-FIBMAP implementation takes the inode mutex, but the FIBMAP ioctl doesn't. > If you are implementing a tool to use this, I would code it to try > FIEMAP first, then FIBMAP (if it is running as root, or it gets > fixed in some future kernel), then just do without (as it most likely > does already today). If FIBMAP is unsafe, it's likely exposed by concurrent changes to the file, so using it would still be unsafe for backup purposes. And I really only need the number of the first block. (I want to optimize reading of Maildir-style folders, mainly for backup purposes.) -- 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
