xfs: add support for lazy direct read bounce buffering

Currently direct I/O reads always bounce buffer the I/O to deal with
the case where userspace is modifying the buffer in-flight while
reading data into it.

This is a very expensive countermeasure for something no sane application
should do, so try to avoid it by reading without a bounce buffer first,
and retrying the read on a checksum failure.  This avoids the cost of
bounce buffering for sanely behave applications.  For the rare case of
an application regularly modifying in-flight buffers, allow forcing the
always bounce buffer behavior through sysfs.  And now that we have that
knob, allow disabling read-side bounce buffering entirely for those who
live fast and dangerous.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>
Link: https://patch.msgid.link/20260909060924.1102037-14-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>

0 files changed, 0 insertions, 0 deletions