dax: rip out get_block based IO support
No one uses functions using the get_block callback anymore. Rip them
out and update documentation.
Reviewed-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
diff --git a/Documentation/filesystems/dax.txt b/Documentation/filesystems/dax.txt
index 23d18b8..a7e6e14 100644
--- a/Documentation/filesystems/dax.txt
+++ b/Documentation/filesystems/dax.txt
@@ -58,22 +58,22 @@
Filesystem support consists of
- adding support to mark inodes as being DAX by setting the S_DAX flag in
i_flags
-- implementing the direct_IO address space operation, and calling
- dax_do_io() instead of blockdev_direct_IO() if S_DAX is set
+- implementing ->read_iter and ->write_iter operations which use dax_iomap_rw()
+ when inode has S_DAX flag set
- implementing an mmap file operation for DAX files which sets the
VM_MIXEDMAP and VM_HUGEPAGE flags on the VMA, and setting the vm_ops to
- include handlers for fault, pmd_fault and page_mkwrite (which should
- probably call dax_fault(), dax_pmd_fault() and dax_mkwrite(), passing the
- appropriate get_block() callback)
-- calling dax_truncate_page() instead of block_truncate_page() for DAX files
-- calling dax_zero_page_range() instead of zero_user() for DAX files
+ include handlers for fault, pmd_fault, page_mkwrite, pfn_mkwrite. These
+ handlers should probably call dax_iomap_fault() (for fault and page_mkwrite
+ handlers), dax_iomap_pmd_fault(), dax_pfn_mkwrite() passing the appropriate
+ iomap operations.
+- calling iomap_zero_range() passing appropriate iomap operations instead of
+ block_truncate_page() for DAX files
- ensuring that there is sufficient locking between reads, writes,
truncates and page faults
-The get_block() callback passed to the DAX functions may return
-uninitialised extents. If it does, it must ensure that simultaneous
-calls to get_block() (for example by a page-fault racing with a read()
-or a write()) work correctly.
+The iomap handlers for allocating blocks must make sure that allocated blocks
+are zeroed out and converted to written extents before being returned to avoid
+exposure of uninitialized data through mmap.
These filesystems may be used for inspiration:
- ext2: see Documentation/filesystems/ext2.txt