Dave Chinner wrote: > On Thu, Jun 26, 2008 at 01:19:51PM +0100, Jamie Lokier wrote: >> Andreas Dilger wrote: >>>> Is there a reason why fsync() before calling FIEMAP is unsuitable? >>> This was added because the xfsbmap operation always did an fsync before >>> returning the extents. I don't think it is strictly required, but it >>> isn't harmful either. >> It's not harmful but suggests it might do something important - >> e.g. provide atomicity between the fsync and getting extends. > > It does precisely that. xfs does via the bmap ioctl, but the generic fiemap implementation does not. It probably should be removed from the vfs level: + if (fieinfo.fi_flags & FIEMAP_FLAG_SYNC) + filemap_write_and_wait(inode->i_mapping); and let the filesystem handle it in an atomic way? >>>>> * FIEMAP_FLAG_XATTR >>>>> If this flag is set, the extents returned will describe the inodes >>>>> extended attribute lookup tree, instead of it's data tree. >>>> What is this for? The meaning of the xattr tree sounds rather >>>> filesystem specific to me. >>> This is to return the location of the xattr blocks for the inode. >> Some filesystems will store xattrs as metadata - in exactly the same >> as, say, the inode itself, it's permissions, mappings etc. >> >> I'm not sure why xattrs get special treatment, compared with a >> hypothetical FIEMAP_FLAG_METADATA for example, indicating which >> physical blocks contain the inode itself, or it's other auxiliary >> information. > > Because xattrs tend to contain user data, not metadata? Agreed, I don't see anything particularly strange about returning the xattr mapping, and to me it's not particularly fs specific (well, the detailed format of the on-disk data might be, i.e. the layout of names & values within that blob of data, but it is still user data... I guess it's something of a grey area). -Eric -- 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
