On Thu, 23 Jan 2014, Matthew Wilcox wrote:
> On Wed, Jan 22, 2014 at 03:51:56PM -0700, Ross Zwisler wrote:
> > > + if (hole) {
> > > addr = NULL;
> > > - hole = true;
> > > size = bh->b_size;
> > > + } else {
> > > + unsigned first;
> > > + retval = xip_get_addr(inode, bh, &addr);
> > > + if (retval < 0)
> > > + break;
> > > + size = retval;
> > > + first = offset - (block << inode->i_blkbits);
> > > + if (buffer_unwritten(bh))
> > > + memset(addr, 0, first);
> > > + addr += first;
> >
> > + size -= first;
> >
> > This is needed so that we don't overrun the XIP buffer we are given in the
> > event that our user buffer >= our XIP buffer and the start of our I/O isn't
> > block aligned.
>
> You're right! Thank you! However, we also need it for the hole ==
> true case, don't we? So maybe something like this, incrementally on top of
> patch 22/22:
>
> P.S. Can someone come up with a better name for this variable than 'first'?
> I'd usually use 'offset', but that's already taken. 'annoying_bit' seems a
> bit judgemental. 'misaligned', maybe? 'skip' or 'seek' like dd uses?
>
> diff --git a/fs/xip.c b/fs/xip.c
> index 92157ff..1ae00db 100644
> --- a/fs/xip.c
> +++ b/fs/xip.c
> @@ -103,6 +103,7 @@ static ssize_t xip_io(int rw, struct inode *inode, const struct iovec *iov,
>
> if (max == offset) {
> sector_t block = offset >> inode->i_blkbits;
> + unsigned first = offset - (block << inode->i_blkbits);
> long size;
> memset(bh, 0, sizeof(*bh));
> bh->b_size = ALIGN(end - offset, PAGE_SIZE);
> @@ -121,14 +122,12 @@ static ssize_t xip_io(int rw, struct inode *inode, const struct iovec *iov,
>
> if (hole) {
> addr = NULL;
> - size = bh->b_size;
> + size = bh->b_size - first;
> } else {
> - unsigned first;
> retval = xip_get_addr(inode, bh, &addr);
> if (retval < 0)
> break;
> - size = retval;
> - first = offset - (block << inode->i_blkbits);
> + size = retval - first;
> if (buffer_unwritten(bh))
> memset(addr, 0, first);
> addr += first;
Yep, this seems right to me.
Maybe "misalignment"? Seems more descriptive (if a bit long), but I don't
know if there are other, better existing conventions.
- Ross
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