From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:47101) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aOqlX-0003yq-Hv for qemu-devel@nongnu.org; Thu, 28 Jan 2016 12:53:56 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1aOqlT-0007FU-HB for qemu-devel@nongnu.org; Thu, 28 Jan 2016 12:53:55 -0500 Received: from mx1.redhat.com ([209.132.183.28]:34672) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aOqlT-0007FN-9C for qemu-devel@nongnu.org; Thu, 28 Jan 2016 12:53:51 -0500 Received: from int-mx13.intmail.prod.int.phx2.redhat.com (int-mx13.intmail.prod.int.phx2.redhat.com [10.5.11.26]) by mx1.redhat.com (Postfix) with ESMTPS id CEDF019CBD8 for ; Thu, 28 Jan 2016 17:53:50 +0000 (UTC) Date: Thu, 28 Jan 2016 17:53:46 +0000 From: "Dr. David Alan Gilbert" Message-ID: <20160128175346.GC2911@work-vm> References: <1452599056-27357-1-git-send-email-berrange@redhat.com> <1452599056-27357-4-git-send-email-berrange@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1452599056-27357-4-git-send-email-berrange@redhat.com> Subject: Re: [Qemu-devel] [PATCH v1 03/22] migration: ensure qemu_fflush() always writes full data amount List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Daniel P. Berrange" Cc: Amit Shah , qemu-devel@nongnu.org, Juan Quintela * Daniel P. Berrange (berrange@redhat.com) wrote: > The QEMUFile writev_buffer / put_buffer functions are expected > to write out the full set of requested data, blocking until > complete. The qemu_fflush() caller does not expect to deal with > partial writes. Clarify the function comments and add a sanity > check to the code to catch mistaken implementations. > > Signed-off-by: Daniel P. Berrange > --- > include/migration/qemu-file.h | 6 ++++-- > migration/qemu-file.c | 16 ++++++++++++---- > 2 files changed, 16 insertions(+), 6 deletions(-) > > diff --git a/include/migration/qemu-file.h b/include/migration/qemu-file.h > index b5d08d2..5debe8c 100644 > --- a/include/migration/qemu-file.h > +++ b/include/migration/qemu-file.h > @@ -29,7 +29,8 @@ > > /* This function writes a chunk of data to a file at the given position. > * The pos argument can be ignored if the file is only being used for > - * streaming. The handler should try to write all of the data it can. > + * streaming. The handler must write all of the data or return a negative > + * errno value. > */ > typedef ssize_t (QEMUFilePutBufferFunc)(void *opaque, const uint8_t *buf, > int64_t pos, size_t size); > @@ -55,7 +56,8 @@ typedef int (QEMUFileCloseFunc)(void *opaque); > typedef int (QEMUFileGetFD)(void *opaque); > > /* > - * This function writes an iovec to file. > + * This function writes an iovec to file. The handler must write all > + * of the data or return a negative errno value. > */ > typedef ssize_t (QEMUFileWritevBufferFunc)(void *opaque, struct iovec *iov, > int iovcnt, int64_t pos); > diff --git a/migration/qemu-file.c b/migration/qemu-file.c > index 0bbd257..f89e64e 100644 > --- a/migration/qemu-file.c > +++ b/migration/qemu-file.c > @@ -107,11 +107,13 @@ bool qemu_file_is_writable(QEMUFile *f) > * Flushes QEMUFile buffer > * > * If there is writev_buffer QEMUFileOps it uses it otherwise uses > - * put_buffer ops. > + * put_buffer ops. This will flush all pending data. If data was > + * only partially flushed, it will set an error state. > */ > void qemu_fflush(QEMUFile *f) > { > ssize_t ret = 0; > + ssize_t expect = 0; > > if (!qemu_file_is_writable(f)) { > return; > @@ -119,21 +121,27 @@ void qemu_fflush(QEMUFile *f) > > if (f->ops->writev_buffer) { > if (f->iovcnt > 0) { > + expect = iov_size(f->iov, f->iovcnt); > ret = f->ops->writev_buffer(f->opaque, f->iov, f->iovcnt, f->pos); > } > } else { > if (f->buf_index > 0) { > + expect = f->buf_index; > ret = f->ops->put_buffer(f->opaque, f->buf, f->pos, f->buf_index); > } > } > + > if (ret >= 0) { > f->pos += ret; > } > - f->buf_index = 0; > - f->iovcnt = 0; > - if (ret < 0) { > + /* We expect the QEMUFile write impl to send the full > + * data set we requested, so sanity check that. > + */ > + if (ret < 0 || ret != expect) { > qemu_file_set_error(f, ret); You could simplify that to if (ret != expect) couldn't you? In the case you're trying to guard against, the value past to qemu_file_set_error is potentially truncated; which in the worst case could make it appear as success; although I doubt that can happen in our uses. Reviewed-by: Dr. David Alan Gilbert Dave > } > + f->buf_index = 0; > + f->iovcnt = 0; > } > > void ram_control_before_iterate(QEMUFile *f, uint64_t flags) > -- > 2.5.0 > -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK