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dax: rip out get_block based IO support

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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>
This commit is contained in:
Jan Kara
2016-11-20 20:48:36 -05:00
committed by Theodore Ts'o
parent 00697eed38
commit dd936e4313
3 changed files with 11 additions and 338 deletions
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22
Documentation/filesystems/dax.txt
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@@ -58,22 +58,22 @@ Implementation Tips for Filesystem Writers
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