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Re: [Qemu-devel] [PATCH v5 07/11] iov: add iov_discard() to remove data
From: |
Stefan Hajnoczi |
Subject: |
Re: [Qemu-devel] [PATCH v5 07/11] iov: add iov_discard() to remove data |
Date: |
Thu, 6 Dec 2012 15:07:13 +0100 |
User-agent: |
Mutt/1.5.21 (2010-09-15) |
On Thu, Dec 06, 2012 at 01:36:42PM +0200, Michael S. Tsirkin wrote:
> On Wed, Dec 05, 2012 at 09:47:06PM +0100, Stefan Hajnoczi wrote:
> > The iov_discard() function removes data from the front or back of the
> > vector. This is useful when peeling off header/footer structs.
> >
> > Signed-off-by: Stefan Hajnoczi <address@hidden>
> > ---
> > iov.c | 41 +++++++++++++++++++++++++++++++++++++++++
> > iov.h | 13 +++++++++++++
> > 2 files changed, 54 insertions(+)
> >
> > diff --git a/iov.c b/iov.c
> > index a81eedc..6eed089 100644
> > --- a/iov.c
> > +++ b/iov.c
> > @@ -354,3 +354,44 @@ size_t qemu_iovec_memset(QEMUIOVector *qiov, size_t
> > offset,
> > {
> > return iov_memset(qiov->iov, qiov->niov, offset, fillc, bytes);
> > }
> > +
> > +size_t iov_discard(struct iovec **iov, unsigned int *iov_cnt, ssize_t
> > bytes)
> > +{
> > + size_t total = 0;
> > + struct iovec *cur;
> > + int direction;
> > +
> > + if (*iov_cnt == 0) {
> > + return 0;
> > + }
> > +
> > + if (bytes < 0) {
> > + bytes = -bytes;
> > + direction = -1;
> > + cur = *iov + (*iov_cnt - 1);
> > + } else {
> > + direction = 1;
> > + cur = *iov;
> > + }
> > +
> > + while (*iov_cnt > 0) {
> > + if (cur->iov_len > bytes) {
> > + if (direction > 0) {
> > + cur->iov_base += bytes;
> > + }
> > + cur->iov_len -= bytes;
> > + total += bytes;
> > + break;
> > + }
> > +
> > + bytes -= cur->iov_len;
> > + total += cur->iov_len;
> > + cur += direction;
> > + *iov_cnt -= 1;
> > + }
> > +
> > + if (direction > 0) {
> > + *iov = cur;
> > + }
> > + return total;
> > +}
> > diff --git a/iov.h b/iov.h
> > index 34c8ec9..d6d1fa6 100644
> > --- a/iov.h
> > +++ b/iov.h
> > @@ -95,3 +95,16 @@ void iov_hexdump(const struct iovec *iov, const unsigned
> > int iov_cnt,
> > unsigned iov_copy(struct iovec *dst_iov, unsigned int dst_iov_cnt,
> > const struct iovec *iov, unsigned int iov_cnt,
> > size_t offset, size_t bytes);
> > +
> > +/*
> > + * Remove a given number of bytes from the front or back of a vector.
> > + * This may update iov and/or iov_cnt to exclude iovec elements that are
> > + * no longer required.
> > + *
> > + * Data is discarded from the front of the vector if bytes is positive and
> > + * from the back of the vector if bytes is negative.
>
> I think I already commented on this: I think this interface is too tricky,
> and use of ssize_t is a bad idea since most of code uses size_t:
> you might start getting integer overflow errors if you convert.
>
> Better to have
> size_t iov_discard_front(struct iovec **iov, unsigned int *iov_cnt, ssize_t
> bytes);
> size_t iov_discard_back(struct iovec **iov, unsigned int *iov_cnt, ssize_t
> bytes);
>
> which explicitly do the right thing.
>
> The fix up users to use size_t everywhere.
Okay, will split into front/back.
Stefan
- Re: [Qemu-devel] [PATCH v5 04/11] dataplane: add virtqueue vring code, (continued)
- [Qemu-devel] [PATCH v5 05/11] dataplane: add event loop, Stefan Hajnoczi, 2012/12/05
- [Qemu-devel] [PATCH v5 06/11] dataplane: add Linux AIO request queue, Stefan Hajnoczi, 2012/12/05
- [Qemu-devel] [PATCH v5 07/11] iov: add iov_discard() to remove data, Stefan Hajnoczi, 2012/12/05
- [Qemu-devel] [PATCH v5 11/11] virtio-blk: add x-data-plane=on|off performance feature, Stefan Hajnoczi, 2012/12/05
- [Qemu-devel] [PATCH v5 09/11] iov: add qemu_iovec_concat_iov(), Stefan Hajnoczi, 2012/12/05
- [Qemu-devel] [PATCH v5 08/11] test-iov: add iov_discard() testcase, Stefan Hajnoczi, 2012/12/05
- [Qemu-devel] [PATCH v5 10/11] dataplane: add virtio-blk data plane code, Stefan Hajnoczi, 2012/12/05
- Re: [Qemu-devel] [PATCH v5 10/11] dataplane: add virtio-blk data plane code, Michael S. Tsirkin, 2012/12/06