On Fri, Mar 16, 2018 at 12:50:27AM -0700, Christoph Hellwig wrote:
> > DIF (PI) emulation doesn't work when a target uses async I/O, because
> > DIF metadata is saved in a separate file, and it is another non-trivial
> > task how to synchronize writing in two files, so that a following read
> > operation always returns a consisten metadata for a specified block.
>
> There literally is no way to do that, even without aio. The file
> DIF implementation should probably regarded as an early bringup /
> prototype tool, not something really usable.
>
> > +static void cmd_rw_aio_do_completion(struct target_core_file_cmd *cmd)
> > +{
> > + if (!atomic_dec_and_test(&cmd->ref))
> > + return;
>
> There is no need for reference counting. If the read_iter/write iter
> method returns -EIOCBQUEUED the completion callback needs to complete
> the I/O and free the structure, else the method caller.
I was near to send a final version, but I decided to investigate how a
reference counter was appeared in drivers/block/loop.c:
commit 92d773324b7edbd36bf0c28c1e0157763aeccc92
Author: Shaohua Li <shli@xxxxxx>
Date: Fri Sep 1 11:15:17 2017 -0700
block/loop: fix use after free
lo_rw_aio->call_read_iter->
1 aops->direct_IO
2 iov_iter_revert
lo_rw_aio_complete could happen between 1 and 2, the bio and bvec
could
be freed before 2, which accesses bvec.
Signed-off-by: Shaohua Li <shli@xxxxxx>
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
This commit looks reasonable, doesn't it? In out case, bvec-s are
freed from the callback too.
>
> > + if (!(fd_dev->fbd_flags & FDBD_HAS_BUFFERED_IO_WCE))
> > + aio_cmd->iocb.ki_flags |= IOCB_DIRECT;
>
> aio without IOCB_DIRECT doesn't make any sense. But the WCE flag
> really has nothing to do with buffers vs direct I/O anyway.
>
> > + if (is_write)
> > + ret = call_write_iter(file, &aio_cmd->iocb, &iter);
> > + else
> > + ret = call_read_iter(file, &aio_cmd->iocb, &iter);
>
> Please call the methods directly instead of through the wrappers.
>
> > +
> > static int fd_do_rw(struct se_cmd *cmd, struct file *fd,
> > u32 block_size, struct scatterlist *sgl,
> > u32 sgl_nents, u32 data_length, int is_write)
> > @@ -536,6 +626,7 @@ fd_execute_rw(struct se_cmd *cmd, struct scatterlist *sgl, u32 sgl_nents,
> > struct file *pfile = fd_dev->fd_prot_file;
> > sense_reason_t rc;
> > int ret = 0;
> > + int aio = fd_dev->fbd_flags & FDBD_HAS_ASYNC_IO;
> > /*
> > * We are currently limited by the number of iovecs (2048) per
> > * single vfs_[writev,readv] call.
> > @@ -550,7 +641,11 @@ fd_execute_rw(struct se_cmd *cmd, struct scatterlist *sgl, u32 sgl_nents,
> > * Call vectorized fileio functions to map struct scatterlist
> > * physical memory addresses to struct iovec virtual memory.
> > */
> > - if (data_direction == DMA_FROM_DEVICE) {
> > + if (aio) {
>
> fd_execute_rw shares basically no code with the aio case. I'd rather
> have a very high level wrapper here:
>
> static sense_reason_t
> fd_execute_rw(struct se_cmd *cmd, struct scatterlist *sgl, u32 sgl_nents,
> enum dma_data_direction data_direction)
> {
> if (FD_DEV(cmd->se_dev)->fbd_flags & FDBD_HAS_ASYNC_IO)
> return fd_execute_rw_aio(cmd, sgl, sgl_nents, dma_direction);
> return fd_execute_rw_buffered(cmd, sgl, sgl_nents, dma_direction);
> }
>
> and keep the code separate.
>
