On Sat, May 24, 2008 at 05:01:48PM -0700, Mark Fasheh wrote:
> * FIEMAP_FLAG_HSM_READ
> If the extent is offline, retrieve it before mapping and do not flag
> it as FIEMAP_EXTENT_SECONDARY. This flag has no effect if the file
> system does not support HSM.
Given that there's no HSM support in mainline this should not be added.
It'll be useful once we add proper HSM support, though :)
> * 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.
> struct fiemap_extent_info {
> unsigned int fi_flags; /* Flags as passed from user */
> unsigned int fi_extents_mapped; /* Number of mapped extents */
> unsigned int fi_extents_max; /* Size of fiemap_extent array */
> char *fi_extents_start; /* Start of fiemap_extent array */
> };
Why is this passes a structure instead of individual arguments?
Also why isn't fi_extents_start properly typed?
> If the request has the FIEMAP_FLAG_NUM_EXTENTS flag set, then calling
> this helper is not necessary and fi_extents_mapped can be set
> directly.
Sounds like the count number of extents request should be a separate
ioctl and separate filesystem entry point instead of overloading FIEMAP.
Just define a simple FIECOUNT ioctl.
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