On Wed, Aug 28, 2019 at 10:26:19PM +0200, Jan Kara wrote:
> On Mon 12-08-19 22:53:26, Matthew Bobrowski wrote:
> > This patch introduces a new direct IO write code path implementation
> > that makes use of the iomap infrastructure.
> >
> > All direct IO write operations are now passed from the ->write_iter() callback
> > to the new function ext4_dio_write_iter(). This function is responsible for
> > calling into iomap infrastructure via iomap_dio_rw(). Snippets of the direct
> > IO code from within ext4_file_write_iter(), such as checking whether the IO
> > request is unaligned asynchronous IO, or whether it will ber overwriting
> > allocated and initialized blocks has been moved out and into
> > ext4_dio_write_iter().
> >
> > The block mapping flags that are passed to ext4_map_blocks() from within
> > ext4_dio_get_block() and friends have effectively been taken out and
> > introduced within the ext4_iomap_begin(). If ext4_map_blocks() happens to have
> > instantiated blocks beyond the i_size, then we attempt to place the inode onto
> > the orphan list. Despite being able to perform i_size extension checking
> > earlier on in the direct IO code path, it makes most sense to perform this bit
> > post successful block allocation.
> >
> > The ->end_io() callback ext4_dio_write_end_io() is responsible for removing
> > the inode from the orphan list and determining if we should truncate a failed
> > write in the case of an error. We also convert a range of unwritten extents to
> > written if IOMAP_DIO_UNWRITTEN is set and perform the necessary
> > i_size/i_disksize extension if the iocb->ki_pos + dio->size > i_size_read(inode).
> >
> > In the instance of a short write, we fallback to buffered IO and complete
> > whatever is left the 'iter'. Any blocks that may have been allocated in
> > preparation for direct IO will be reused by buffered IO, so there's no issue
> > with leaving allocated blocks beyond EOF.
> >
> > Signed-off-by: Matthew Bobrowski <mbobrowski@xxxxxxxxxxxxxx>
> > ---
> > fs/ext4/file.c | 227 ++++++++++++++++++++++++++++++++++++++++----------------
> > fs/ext4/inode.c | 42 +++++++++--
> > 2 files changed, 199 insertions(+), 70 deletions(-)
>
> Overall this is very nice. Some smaller comments below.
>
> > @@ -235,6 +244,34 @@ static ssize_t ext4_write_checks(struct kiocb *iocb, struct iov_iter *from)
> > return iov_iter_count(from);
> > }
> >
> > +static ssize_t ext4_buffered_write_iter(struct kiocb *iocb,
> > + struct iov_iter *from)
> > +{
> > + ssize_t ret;
> > + struct inode *inode = file_inode(iocb->ki_filp);
> > +
> > + if (!inode_trylock(inode)) {
> > + if (iocb->ki_flags & IOCB_NOWAIT)
> > + return -EOPNOTSUPP;
> > + inode_lock(inode);
> > + }
>
> Currently there's no support for IOCB_NOWAIT for buffered IO so you can
> replace this with "inode_lock(inode)".
IOCB_NOWAIT is supported for buffered reads. It is not supported on
buffered writes (as yet), so this should return EOPNOTSUPP if
IOCB_NOWAIT is set, regardless of whether the lock can be grabbed or
not.
Cheers,
Dave.
--
Dave Chinner
david@xxxxxxxxxxxxx
