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SubjectRe: [PATCH -next 1/1] iomap: Fix a false positive of UBSAN in iomap_seek_data()
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On 2021/7/5 11:43, Matthew Wilcox wrote:
> On Mon, Jul 05, 2021 at 11:29:44AM +0800, Leizhen (ThunderTown) wrote:
>> I've thought about it, and that "if" statement can be removed as follows:
>
> I think this really misses Christoph's point. He's looking for
> something more like this:

Yes, I know that. I need to get rid of the "if" judgment first, and then I can
modify iomap_seek_data() according to Christoph's point. Otherwise there are too
many conversions from "length" to "size - offset" and the code doesn't look clear.

>
> @@ -83,27 +83,23 @@ loff_t
> iomap_seek_data(struct inode *inode, loff_t offset, const struct iomap_ops *ops)
> {
> loff_t size = i_size_read(inode);
> - loff_t length = size - offset;
> loff_t ret;
>
> /* Nothing to be found before or beyond the end of the file. */
> if (offset < 0 || offset >= size)
> return -ENXIO;
>
> - while (length > 0) {
> + while (offset < size) {
> ret = iomap_apply(inode, offset, length, IOMAP_REPORT, ops,
> &offset, iomap_seek_data_actor);
> if (ret < 0)
> return ret;
> if (ret == 0)
> - break;
> + return offset;
>
> offset += ret;
> - length -= ret;
> }
>
> - if (length <= 0)
> - return -ENXIO;
> - return offset;
> + return -ENXIO;
> }
> EXPORT_SYMBOL_GPL(iomap_seek_data);
>
> (not even slightly tested)
>
> .
>

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