2007-08-29 10:13:27

by Kalpak Shah

[permalink] [raw]
Subject: [PATCH] FIEMAP ioctl


Recently there was discussion about an "FIle Extent MAP"(FIEMAP) ioctl for efficiently mapping the extents and holes of a file. This will be many times more efficient than FIBMAP by cutting down the number of ioctls.

This patch implements this ioctl. Ted, in this patch I have used ioctl nunber 10 for FIEMAP. We need to make sure that the ioctl number in our releases and upstream is same. So can you please advise if we can register ioctl no 10 for FIEMAP or if I need to change it?

Let me just mention the the structures and flags used in FIEMAP for people to have a quick review:

struct fiemap_extent {
__u64 fe_offset; /* 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)*/

* fiemap is not ext4-specific and should be moved into fs.h eventually.

struct fiemap {
__u64 fm_start; /* logical starting byte offset (in/out) */
__u64 fm_length; /* logical length of map (in/out) */
__u32 fm_flags; /* FIEMAP_FLAG_* flags for request (in/out) */
__u32 fm_extent_count; /* number of extents in fm_extents (in/out) */
__u64 fm_unused;
struct fiemap_extent fm_extents[0];

#define FIEMAP_FLAG_SYNC 0x00000001 /* sync file data before map */
#define FIEMAP_FLAG_HSM_READ 0x00000002 /* get data from HSM before map */
#define FIEMAP_FLAG_NUM_EXTENTS 0x00000004 /* return only number of extents */
#define FIEMAP_FLAG_INCOMPAT 0xff000000 /* error for unknown flags in here */

#define FIEMAP_EXTENT_HOLE 0x00000001 /* has no data or space allocation */
#define FIEMAP_EXTENT_UNWRITTEN 0x00000002 /* space allocated, but no data */
#define FIEMAP_EXTENT_UNMAPPED 0x00000004 /* has data but no space allocation*/
#define FIEMAP_EXTENT_ERROR 0x00000008 /* mapping error, errno in fe_start*/
#define FIEMAP_EXTENT_NO_DIRECT 0x00000010 /* cannot access data directly */
#define FIEMAP_EXTENT_LAST 0x00000020 /* last extent in the file */
#define FIEMAP_EXTENT_DELALLOC 0x00000040 /* has data but not yet written,
* must have EXTENT_UNKNOWN set */
#define FIEMAP_EXTENT_SECONDARY 0x00000080 /* data (also) in secondary storage,
* not in primary if EXTENT_UNKNOWN*/
#define FIEMAP_EXTENT_EOF 0x00000100 /* if fm_start+fm_len is beyond EOF*/

checkpatch.pl has been run on this patch and did not report any errors.

Signed-off-by: Andreas Dilger <[email protected]>
Signed-off-by: Kalpak Shah <[email protected]>


ext4-fiemap.patch (9.35 kB)