[PATCH] ntfs: add code to make FIBMAP ioctl work

[Sergei Antonov <saproj@gmail.com>]

Implement ntfs_bmap() function for the "bmap" address space operation.
Now user space programs can send FIBMAP ioctl to get files' placement on
NTFS the same way they can do it on a number of other linux filesystems.

The result is returned in FIGETBSZ units, which is equal to sector size
in ntfs driver. An error value zero is returned for resident, compressed,
encrypted files, and for holes in sparse files.

Tested on drives with different sector sizes and different cluster sizes.

Cc: Anton Altaparmakov <aia21@cantab.net>
Signed-off-by: Sergei Antonov <saproj@gmail.com>
---
 fs/ntfs/aops.c | 31 +++++++++++++++++++++++++++++++
 1 file changed, 31 insertions(+)

diff --git a/fs/ntfs/aops.c b/fs/ntfs/aops.c
index d267ea6..3972b6b 100644
--- a/fs/ntfs/aops.c
+++ b/fs/ntfs/aops.c
@@ -1538,6 +1538,36 @@ err_out:
 
 #endif	/* NTFS_RW */
 
+static sector_t ntfs_bmap(struct address_space *mapping, sector_t block)
+{
+	struct inode *vi = mapping->host;
+	ntfs_inode *ni = NTFS_I(vi);
+	ntfs_volume *vol = ni->vol;
+	const unsigned clust2sect_bits = vol->cluster_size_bits -
+		vol->sector_size_bits;
+	const sector_t clust2sect_mask = (1 << clust2sect_bits) - 1;
+	LCN lcn;
+
+	BUG_ON(S_ISDIR(vi->i_mode));
+	ntfs_debug("Requested LCN for block %llu.", (unsigned long long)block);
+	if (!NInoNonResident(ni) || NInoCompressed(ni) || NInoEncrypted(ni))
+		return 0;
+
+	down_read(&ni->runlist.lock);
+	lcn = ntfs_attr_vcn_to_lcn_nolock(ni, block >> clust2sect_bits, false);
+	up_read(&ni->runlist.lock);
+
+	if (lcn < 0) {
+		if (lcn == LCN_HOLE)
+			ntfs_warning(vol->sb, "Cannot get LCN for a hole.");
+		else
+			ntfs_error(vol->sb, "Error getting LCN: %lld.", lcn);
+		return 0;
+	}
+
+	return (lcn << clust2sect_bits) + (block & clust2sect_mask);
+}
+
 /**
  * ntfs_aops - general address space operations for inodes and attributes
  */
@@ -1546,6 +1576,7 @@ const struct address_space_operations ntfs_aops = {
 #ifdef NTFS_RW
 	.writepage	= ntfs_writepage,	/* Write dirty page to disk. */
 #endif /* NTFS_RW */
+	.bmap		= ntfs_bmap,		/* Map file offset to volume. */
 	.migratepage	= buffer_migrate_page,	/* Move a page cache page from
 						   one physical page to an
 						   other. */
-- 
2.1.2