On Sep 10, 2008 11:46 -0700, Andrew Morton wrote: > On Wed, 10 Sep 2008 05:49:34 -0700 Mark Fasheh <mfasheh@xxxxxxxx> wrote: > > The following patches are the latest attempt at implementing a > > fiemap ioctl, which can be used by userspace software to get extent > > information for an inode in an efficient manner. > > As these are applicable to all filesystems, Cc:ing only linux-ext4 is > not sufficient. All filesystem developers (at least) need an > opportunity to review and understand these changes. That was an oversight, partly caused because I launched the thread for this on linux-ext4 after an ext4 concall. All previous patches have gone to linux-fsdevel and been through numerous discussions. > > The fiemap ioctl is an efficient method for userspace to get file > > extent mappings. Instead of block-by-block mapping (such as bmap), fiemap > > returns a list of extents. > > The above is, afacit, the only offered rationale for the addition of > these new feature. I don't recall seeing anyone complain about bmap() > inefficiency. In fact I rarely hear of anyone using bmap() at all. > > This rationale needs expanding, please. A lot. There are several reasons for this new API: - it avoids tools like "filefrag" (which currently use FIBMAP) having to do an ioctl for every block in a file, have the kernel map that block from an on-disk extent (in most newer filesystems), then re-assemble the extents in userspace. - it works with filesystems that are not block based (e.g. NTFS, btrfs, etc) that may align file data on boundaries other than $blocksize boundaries - it provides a much more rich API for finding out about on-disk allocation, such as whether allocated blocks are unwritten (e.g. fallocate), if they are packed along with other data, if the data is in the inode, etc. - it can share existing XFS-specific functionality (which FIEMAP was designed to provide a superset of functionality for) with other filesystems. Cheers, Andreas -- Andreas Dilger Sr. Staff Engineer, Lustre Group Sun Microsystems of Canada, Inc. -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
