From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:50791) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Tgc6q-0006qy-3p for qemu-devel@nongnu.org; Thu, 06 Dec 2012 09:07:38 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Tgc6g-0004iI-DM for qemu-devel@nongnu.org; Thu, 06 Dec 2012 09:07:28 -0500 Received: from mail-wg0-f41.google.com ([74.125.82.41]:49992) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Tgc6g-0004hm-7P for qemu-devel@nongnu.org; Thu, 06 Dec 2012 09:07:18 -0500 Received: by mail-wg0-f41.google.com with SMTP id ds1so287839wgb.4 for ; Thu, 06 Dec 2012 06:07:16 -0800 (PST) Date: Thu, 6 Dec 2012 15:07:13 +0100 From: Stefan Hajnoczi Message-ID: <20121206140713.GA3094@stefanha-thinkpad.redhat.com> References: <1354740430-22452-1-git-send-email-stefanha@redhat.com> <1354740430-22452-8-git-send-email-stefanha@redhat.com> <20121206113642.GM10837@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20121206113642.GM10837@redhat.com> Subject: Re: [Qemu-devel] [PATCH v5 07/11] iov: add iov_discard() to remove data List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Michael S. Tsirkin" Cc: Kevin Wolf , Anthony Liguori , qemu-devel@nongnu.org, Blue Swirl , khoa@us.ibm.com, Stefan Hajnoczi , Paolo Bonzini , asias@redhat.com 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 > > --- > > 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