On Mon, Jan 27, 2014 at 04:32:07PM -0700, Ross Zwisler wrote:
> It looks like we have an additional bit of complexity with the hole case. The
> issue is that for holes, bh->b_size is just the full size of the write as set
> earlier in the function:
>
> bh->b_size = ALIGN(end - offset, PAGE_SIZE);
>
> >From this code it seems like you hoped the call into get_block() would adjust
> bh->b_size to the size of the hole, allowing you to zero just the hole space
> in the user buffer. It doesn't look like it does, though, at least for ext4.
Argh. I got confused. ext4 *has* this information, it just doesn't
propagate it into the bh if it's a hole! Should it? The comments in
the direct IO code imply that it *may*, but doesn't *have* to. What it's
doing now (not touching it) is probably wrong.
> To just assume the current FS block is a hole, we can do something like this:
Yes, this should fix things on an interim basis. Bit inefficient,
but it'll work.
> diff --git a/fs/xip.c b/fs/xip.c
> index 35e401e..e902593 100644
> --- a/fs/xip.c
> +++ b/fs/xip.c
> @@ -122,7 +122,7 @@ static ssize_t xip_io(int rw, struct inode *inode, const struct
>
> if (hole) {
> addr = NULL;
> - size = bh->b_size - first;
> + size = (1 << inode->i_blkbits) - first;
> } else {
> retval = xip_get_addr(inode, bh, &addr);
> if (retval < 0)
>
> --
> To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
> the body of a message to majordomo@xxxxxxxxxxxxxxx
> More majordomo info at http://vger.kernel.org/majordomo-info.html
--
Matthew Wilcox Intel Open Source Technology Centre
"Bill, look, we understand that you're interested in selling us this
operating system, but compare it to ours. We can't possibly take such
a retrograde step."
--
To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
