From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:52288) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZrmFy-0007eN-CX for qemu-devel@nongnu.org; Thu, 29 Oct 2015 08:24:39 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ZrmFv-0000aF-57 for qemu-devel@nongnu.org; Thu, 29 Oct 2015 08:24:38 -0400 Received: from mx3-phx2.redhat.com ([209.132.183.24]:48900) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZrmFu-0000Ze-Tv for qemu-devel@nongnu.org; Thu, 29 Oct 2015 08:24:35 -0400 Date: Thu, 29 Oct 2015 08:24:31 -0400 (EDT) From: Victor Kaplansky Message-ID: <1505951557.40762651.1446121471978.JavaMail.zimbra@redhat.com> In-Reply-To: <1446113893-31921-1-git-send-email-victork@redhat.com> References: <1446113893-31921-1-git-send-email-victork@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH] vhost user: fix documentation of log atomic elements List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: thibaut collet , "Michael S. Tsirkin" , marcandre lureau After looking into linux driver code at hw/virtio/vhost.c, I see that the driver does what spec says. Thus spec the should remain as is, and QEMU need to be fixed on big-endian machines by changing the code in hw/virtio/vhost.c --Victor ----- Original Message ----- From: "Victor Kaplansky" To: qemu-devel@nongnu.org Cc: "thibaut collet" , "marcandre lureau" , "Michael S. Tsirkin" , "changchun ouyang" , "Victor Kaplansky" Sent: Thursday, October 29, 2015 12:20:31 PM Subject: [PATCH] vhost user: fix documentation of log atomic elements Current implementation in hw/virtio/vhost.c accesses the log by 32-bit wide chunks in host native bit and byte endianness. Accessing the log by 8-bit wide chunks, as the spec suggests, will be broken on big-endian hosts. This commit changes the spec to match the implementation. Signed-off-by: Victor Kaplansky --- docs/specs/vhost-user.txt | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/docs/specs/vhost-user.txt b/docs/specs/vhost-user.txt index e0d71e2..3d18771 100644 --- a/docs/specs/vhost-user.txt +++ b/docs/specs/vhost-user.txt @@ -177,9 +177,11 @@ addresses. The log covers from address 0 to the maximum of guest regions. In pseudo-code, to mark page at "addr" as dirty: page = addr / VHOST_LOG_PAGE -log[page / 8] |= 1 << page % 8 +log[page / 32] |= 1 << page % 32 -Use atomic operations, as the log may be concurrently manipulated. +Use atomic operations, as the log may be concurrently +manipulated, and access the log by atomic 32-bit wide elements in +host native bit-level endianness. VHOST_USER_SET_LOG_FD is an optional message with an eventfd in ancillary data, it may be used to inform the master that the log has -- --Victor