Re: [PATCH v2 5/5] dax: handle media errors in dax_do_io

"Verma, Vishal L" <vishal.l.verma(a)intel.com&gt; writes: > > On Fri, 2016-04-15 at 12:11 -0400, Jeff Moyer wrote: > > > > Vishal Verma <vishal.l.verma(a)intel.com&gt; 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.