From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:50334) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1TgZi3-0007IO-6d for qemu-devel@nongnu.org; Thu, 06 Dec 2012 06:33:55 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1TgZhu-0003oQ-Fx for qemu-devel@nongnu.org; Thu, 06 Dec 2012 06:33:43 -0500 Received: from mx1.redhat.com ([209.132.183.28]:3956) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1TgZhu-0003oH-7i for qemu-devel@nongnu.org; Thu, 06 Dec 2012 06:33:34 -0500 Date: Thu, 6 Dec 2012 13:36:42 +0200 From: "Michael S. Tsirkin" Message-ID: <20121206113642.GM10837@redhat.com> References: <1354740430-22452-1-git-send-email-stefanha@redhat.com> <1354740430-22452-8-git-send-email-stefanha@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1354740430-22452-8-git-send-email-stefanha@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: Stefan Hajnoczi Cc: Kevin Wolf , Anthony Liguori , qemu-devel@nongnu.org, Blue Swirl , khoa@us.ibm.com, Paolo Bonzini , asias@redhat.com 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. > + * > + * The number of bytes actually discarded is returned. This number may be > + * smaller than requested if the vector is too small. > + */ > +size_t iov_discard(struct iovec **iov, unsigned int *iov_cnt, ssize_t bytes); > -- > 1.8.0.1