On Fri, 2016-04-15 at 13:11 -0400, Jeff Moyer wrote:
> "Verma, Vishal L" <vishal.l.verma@xxxxxxxxx> writes:
>
> >
> > On Fri, 2016-04-15 at 12:11 -0400, Jeff Moyer wrote:
> > >
> > > Vishal Verma <vishal.l.verma@xxxxxxxxx> writes:
> > > >
> > > > + if (IS_DAX(inode)) {
> > > > + ret = dax_do_io(iocb, inode, iter, offset,
> > > > blkdev_get_block,
> > > > NULL, DIO_SKIP_DIO_COUNT);
> > > > - return __blockdev_direct_IO(iocb, inode,
> > > > I_BDEV(inode),
> > > > iter, offset,
> > > > + if (ret == -EIO && (iov_iter_rw(iter) ==
> > > > WRITE))
> > > > + ret_saved = ret;
> > > > + else
> > > > + return ret;
> > > > + }
> > > > +
> > > > + ret = __blockdev_direct_IO(iocb, inode, I_BDEV(inode),
> > > > iter, offset,
> > > > blkdev_get_block, NULL,
> > > > NULL,
> > > > DIO_SKIP_DIO_COUNT);
> > > > + if (ret < 0 && ret_saved)
> > > > + return ret_saved;
> > > > +
> > > Hmm, did you just break async DIO? I think you did! :)
> > > __blockdev_direct_IO can return -EIOCBQUEUED, and you've now
> > > turned
> > > that
> > > into -EIO. Really, I don't see a reason to save that first
> > > -EIO. The
> > > same applies to all instances in this patch.
> > The reason I saved it was if __blockdev_direct_IO fails for some
> > reason, we should return the original cause o the error, which was
> > an
> > EIO.. i.e. we shouldn't be hiding the EIO if the direct_IO fails
> > with
> > something else..
> OK.
>
> >
> > But, how does _EIOCBQUEUED work? Maybe we need an exception for it?
> For async direct I/O, only the setup phase of the I/O is performed
> and
> then we return to the caller. -EIOCBQUEUED signifies this.
>
> You're heading towards code that looks like this:
>
> if (IS_DAX(inode)) {
> ret = dax_do_io(iocb, inode, iter, offset,
> blkdev_get_block,
> NULL, DIO_SKIP_DIO_COUNT);
> if (ret == -EIO && (iov_iter_rw(iter) == WRITE))
> ret_saved = ret;
> else
> return ret;
> }
>
> ret = __blockdev_direct_IO(iocb, inode, I_BDEV(inode), iter,
> offset,
> blkdev_get_block, NULL, NULL,
> DIO_SKIP_DIO_COUNT);
> if (ret < 0 && ret != -EIOCBQUEUED && ret_saved)
> return ret_saved;
>
> There's a lot of special casing here, so you might consider adding
> comments.
Correct - maybe we should reconsider wrapper-izing this? :)
Thanks for the explanation and for catching this. I'll fix it for the
next revision.
>
> Cheers,
> Jeff
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