[PATCH v2 0/2] nilfs2: eliminate blockdev_direct_IO() call

[Viacheslav Dubeyko <slava@dubeyko.com>]

The patchset eliminates blockdev_direct_IO() from
nilfs2 entirely. It adds iomap.h with declaration of iomaps
operations and iomap.c with implementation of
nilfs_iomap_begin(). The nilfs_direct_IO() and the .direct_IO
callback on nilfs_aops are removed. The nilfs_file_read_iter()
dispatches O_DIRECT reads to iomap_dio_rw() using nilfs_iomap_ops.
Everything else still goes through generic_file_read_iter().
The unnecessary "select LEGACY_DIRECT_IO" has been exchanged on
"select FS_IOMAP" in Kconfig.

v2
The bug has been discovered in nilfs_iomap_begin() of patchset's
first version thanks to Linmao Li.

nilfs_iomap_begin() looks up the filesystem block containing the requested
offset and returns the physical address of that block.  However, it sets
iomap->offset to the original, possibly sub-block, offset while leaving
iomap->addr at the start of the physical block.

iomap_sector() adds the difference between the I/O position and
iomap->offset to iomap->addr.  For an O_DIRECT read at offset 512 on a
filesystem with 4 KiB blocks, the two file offsets are equal and the I/O is
therefore submitted at the start of the physical block instead of 512 bytes
into it.  iomap direct I/O permits this alignment when the device logical
block size is 512 bytes.

Describe mapped and hole extents from the filesystem-block-aligned file
offset.  This makes the physical and file offsets refer to the same byte.
It also prevents a one-block hole mapping from extending into the following
block.

Viacheslav Dubeyko (2):
  nilfs2: add iomap operations for direct I/O
  nilfs2: switch O_DIRECT to iomap based operations

 fs/nilfs2/Kconfig  |  2 +-
 fs/nilfs2/Makefile |  2 +-
 fs/nilfs2/file.c   | 40 ++++++++++++++++++++++++--
 fs/nilfs2/inode.c  | 13 ---------
 fs/nilfs2/iomap.c  | 72 ++++++++++++++++++++++++++++++++++++++++++++++
 fs/nilfs2/iomap.h  | 13 +++++++++
 6 files changed, 124 insertions(+), 18 deletions(-)
 create mode 100644 fs/nilfs2/iomap.c
 create mode 100644 fs/nilfs2/iomap.h

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2.43.0