nilfs2: add iomap operations for direct I/O reads

Add iomap.c and iomap.h with a read-only nilfs_iomap_ops,
wrapping the existing nilfs_bmap_lookup_contig() lookup
to report a mapped range, a real hole, or an EOF-clamped
range to iomap core.

NILFS2 is a log-structured, copy-on-write filesystem:
newly allocated blocks are only given a real disk address
when the segment constructor writes them out as part of a log,
which walks buffer_head lists directly and is not integrated
with the generic address_space writeback path. Because of that,
only the read-only side of the mapping is added - buffered writes,
writeback, and mmap's ->page_mkwrite() will stay on the existing
buffer_head based path (nilfs_get_block(), nilfs_write_begin/end(),
nilfs_writepages(), nilfs_dirty_folio(), block_page_mkwrite()).

Signed-off-by: Viacheslav Dubeyko <slava@dubeyko.com>
Link: https://patch.msgid.link/20260724222745.2107464-2-slava@dubeyko.com
Acked-by: Ryusuke Konishi <konishi.ryusuke@gmail.com>
cc: Christoph Hellwig <hch@lst.de>
cc: Ryusuke Konishi <konishi.ryusuke@gmail.com>
cc: linux-nilfs@vger.kernel.org
cc: linux-fsdevel@vger.kernel.org
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>

0 files changed, 0 insertions, 0 deletions