On Sun, May 25, 2008 at 03:42:03PM -0400, Christoph Hellwig wrote:
> > * FIEMAP_FLAG_LUN_ORDER
> > If the file system stripes file data, this will return contiguous
> > regions of physical allocation, sorted by LUN. Logical offsets may not
> > make sense if this flag is passed. If the file system does not support
> > multiple LUNs, this flag will be ignored.
>
> A LUN doesn't make any sense in filesystem context. That's a
> scsi-centric acronym that doesn't even make sense in a scsi-centric
> filesystem universe because a LUN can of course contain multiple
> partitions. It's also extremly ill-defined when using volume managers.
>
> There's also no filesystems that actually support a single file on
> multiple device in mainline, the only filesystem that supports multiple
> data devices at all (XFS) requires each file to be on a single device.
>
> Once we have a filesystem with real multiple data device support like
> btrfs or a future XFS version we can worry about this and defined
> a different ioctl for it.
>
> >
> > Each extent is described by a single fiemap_extent structure as
> > returned in fm_extents.
> >
> > struct fiemap_extent {
> > __u64 fe_logical;/* logical offset in bytes for the start of
> > * the extent */
> > __u64 fe_physical; /* physical offset in bytes for the start
> > * of the extent */
> > __u64 fe_length; /* length in bytes for the extent */
> > __u32 fe_flags; /* returned FIEMAP_EXTENT_* flags for the extent */
> > __u32 fe_lun; /* logical device number for extent (starting at 0)*/
>
> Again this lun thing is horribly ill-defined. There is no such thing
> as a logic device number in our filesystem terminology.
The vxfs filesystem is capable of having each extent in a file on a
different device. However, I don't think freevxfs supports that.
I do agree that calling each one a "lun" is not really meaningful.
Brad Boyer
flar@xxxxxxxxxxxxx
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