This patch adds direct EXT4_IOC_FIEMAP support to ldiskfs, for Lustre to call
without having to go through do_vfs_ioctl() (which isn't exported, and has a
number of other ioctls which are not suitable for Lustre). The actual FIEMAP
support is already in the kernel/ext4 for normal usage.

Index: linux-stage/fs/ext4/ext4.h
===================================================================
--- linux-stage.orig/fs/ext4/ext4.h
+++ linux-stage/fs/ext4/ext4.h
@@ -405,7 +405,7 @@ struct ext4_new_group_data {
 #define EXT4_IOC_GROUP_ADD		_IOW('f', 8, struct ext4_new_group_input)
 #define EXT4_IOC_MIGRATE		_IO('f', 9)
  /* note ioctl 10 reserved for an early version of the FIEMAP ioctl */
- /* note ioctl 11 reserved for filesystem-independent FIEMAP ioctl */
+#define EXT4_IOC_FIEMAP			_IOWR('f', 11, struct fiemap)
 #define EXT4_IOC_ALLOC_DA_BLKS		_IO('f', 12)
 #define EXT4_IOC_MOVE_EXT		_IOWR('f', 15, struct move_extent)
 
Index: linux-stage/fs/ext4/ioctl.c
===================================================================
--- linux-stage.orig/fs/ext4/ioctl.c
+++ linux-stage/fs/ext4/ioctl.c
@@ -18,6 +18,71 @@
 #include "ext4_jbd2.h"
 #include "ext4.h"
 
+/* So that the fiemap access checks can't overflow on 32 bit machines. */
+#define FIEMAP_MAX_EXTENTS     (UINT_MAX / sizeof(struct fiemap_extent))
+
+static int fiemap_check_ranges(struct super_block *sb,
+			       u64 start, u64 len, u64 *new_len)
+{
+	*new_len = len;
+
+	if (len == 0)
+		return -EINVAL;
+
+	if (start > sb->s_maxbytes)
+		return -EFBIG;
+
+	/*
+	 * Shrink request scope to what the fs can actually handle.
+	 */
+	if ((len > sb->s_maxbytes) ||
+	    (sb->s_maxbytes - len) < start)
+		*new_len = sb->s_maxbytes - start;
+
+	return 0;
+}
+
+int ioctl_fiemap(struct inode *inode, struct file *filp, unsigned long arg)
+{
+	struct fiemap fiemap;
+	u64 len;
+	struct fiemap_extent_info fieinfo = {0, };
+	struct super_block *sb = inode->i_sb;
+	int error = 0;
+
+	if (copy_from_user(&fiemap, (struct fiemap __user *) arg,
+			   sizeof(struct fiemap)))
+		 return -EFAULT;
+
+	if (fiemap.fm_extent_count > FIEMAP_MAX_EXTENTS)
+		return -EINVAL;
+
+	error = fiemap_check_ranges(sb, fiemap.fm_start, fiemap.fm_length,
+				    &len);
+	if (error)
+		return error;
+
+	fieinfo.fi_flags = fiemap.fm_flags;
+	fieinfo.fi_extents_max = fiemap.fm_extent_count;
+	fieinfo.fi_extents_start = (struct fiemap_extent *)(arg + sizeof(fiemap));
+
+	if (fiemap.fm_extent_count != 0 &&
+	    !access_ok(VERIFY_WRITE, (void *)arg,
+		       offsetof(typeof(fiemap), fm_extents[fiemap.fm_extent_count])))
+		return -EFAULT;
+
+	if (fieinfo.fi_flags & FIEMAP_FLAG_SYNC)
+		filemap_write_and_wait(inode->i_mapping);
+
+	error = ext4_fiemap(inode, &fieinfo, fiemap.fm_start, len);
+	fiemap.fm_flags = fieinfo.fi_flags;
+	fiemap.fm_mapped_extents = fieinfo.fi_extents_mapped;
+	if (copy_to_user((char *)arg, &fiemap, sizeof(fiemap)))
+		error = -EFAULT;
+
+	return error;
+}
+
 long ext4_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 {
 	struct inode *inode = filp->f_dentry->d_inode;
@@ -330,6 +395,9 @@ mext_out:
 		mnt_drop_write(filp->f_path.mnt);
 		return err;
 	}
+	case EXT4_IOC_FIEMAP: {
+		return ioctl_fiemap(inode, filp, arg);
+	}
 
 	default:
 		return -ENOTTY;
Index: linux-stage/fs/ext4/fiemap.h
===================================================================
--- /dev/null
+++ linux-stage/fs/ext4/fiemap.h
@@ -0,0 +1,2 @@
+
+#include_next <fiemap.h>