[RFC 08/11] fs: add get_block() to struct inode_operations

[Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>]

To be able to flush dirty pages to media as part of the fsync/msync path
DAX needs to be able to map file offsets to kernel addresses via a
combination of the filesystem's get_block() routine and
bdev_direct_access().  This currently happens in the DAX fault handlers
which receive a get_block() callback directly from the filesystem via a
function parameter.

For the fsync/msync path this doesn't work, though, because DAX is called
not by the filesystem but by the writeback infrastructure which doesn't
know about the filesystem specific get_block() routine.

To handle this we make get_block() an entry in the struct inode_operations
table so that we can access the correct get_block() routine in the
context of the writeback infrastructure.

Signed-off-by: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
---
 fs/ext2/file.c     | 1 +
 fs/ext4/file.c     | 1 +
 fs/xfs/xfs_iops.c  | 1 +
 include/linux/fs.h | 4 ++--
 4 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/fs/ext2/file.c b/fs/ext2/file.c
index 11a42c5..fc1418c 100644
--- a/fs/ext2/file.c
+++ b/fs/ext2/file.c
@@ -202,4 +202,5 @@ const struct inode_operations ext2_file_inode_operations = {
        .get_acl        = ext2_get_acl,
        .set_acl        = ext2_set_acl,
        .fiemap         = ext2_fiemap,
+       .get_block      = ext2_get_block,
 };
diff --git a/fs/ext4/file.c b/fs/ext4/file.c
index 113837e..54d7729 100644
--- a/fs/ext4/file.c
+++ b/fs/ext4/file.c
@@ -720,5 +720,6 @@ const struct inode_operations ext4_file_inode_operations = {
        .get_acl        = ext4_get_acl,
        .set_acl        = ext4_set_acl,
        .fiemap         = ext4_fiemap,
+       .get_block      = ext4_get_block_dax,
 };
 
diff --git a/fs/xfs/xfs_iops.c b/fs/xfs/xfs_iops.c
index 8294132..c58c270 100644
--- a/fs/xfs/xfs_iops.c
+++ b/fs/xfs/xfs_iops.c
@@ -1112,6 +1112,7 @@ static const struct inode_operations xfs_inode_operations 
= {
        .listxattr              = xfs_vn_listxattr,
        .fiemap                 = xfs_vn_fiemap,
        .update_time            = xfs_vn_update_time,
+       .get_block              = xfs_get_blocks_direct,
 };
 
 static const struct inode_operations xfs_dir_inode_operations = {
diff --git a/include/linux/fs.h b/include/linux/fs.h
index f791698..1dca85b 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1679,8 +1679,8 @@ struct inode_operations {
                           umode_t create_mode, int *opened);
        int (*tmpfile) (struct inode *, struct dentry *, umode_t);
        int (*set_acl)(struct inode *, struct posix_acl *, int);
-
-       /* WARNING: probably going away soon, do not use! */
+       int (*get_block)(struct inode *inode, sector_t iblock,
+                       struct buffer_head *bh_result, int create);
 } ____cacheline_aligned;
 
 ssize_t rw_copy_check_uvector(int type, const struct iovec __user * uvector,
-- 
2.1.0