From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([140.186.70.92]:41586) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1RPt2C-0003NQ-3l for qemu-devel@nongnu.org; Mon, 14 Nov 2011 04:41:01 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1RPt2A-0001AR-W8 for qemu-devel@nongnu.org; Mon, 14 Nov 2011 04:41:00 -0500 Received: from mail-iy0-f173.google.com ([209.85.210.173]:45483) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1RPt2A-00017I-RC for qemu-devel@nongnu.org; Mon, 14 Nov 2011 04:40:58 -0500 Received: by mail-iy0-f173.google.com with SMTP id k32so8306342iak.4 for ; Mon, 14 Nov 2011 01:40:58 -0800 (PST) Sender: Paolo Bonzini From: Paolo Bonzini Date: Mon, 14 Nov 2011 10:40:30 +0100 Message-Id: <1321263630-546-7-git-send-email-pbonzini@redhat.com> In-Reply-To: <1321263630-546-1-git-send-email-pbonzini@redhat.com> References: <1321263630-546-1-git-send-email-pbonzini@redhat.com> Subject: [Qemu-devel] [PATCH v2 6/6] scsi-block: always use SG_IO for MMC devices List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: kwolf@redhat.com CD burning messes up the state of the host page cache and host block device. Just pass all operations down to the device, even though that might have slightly worse performance. Everything else just is not reliable in combination with burning. Reported-by: Thomas Schmitt Signed-off-by: Paolo Bonzini --- hw/scsi-disk.c | 16 ++++++++++++++-- 1 files changed, 14 insertions(+), 2 deletions(-) diff --git a/hw/scsi-disk.c b/hw/scsi-disk.c index c2a3864..9b172b4 100644 --- a/hw/scsi-disk.c +++ b/hw/scsi-disk.c @@ -1731,8 +1731,20 @@ static SCSIRequest *scsi_block_new_request(SCSIDevice *d, uint32_t tag, case WRITE_VERIFY_10: case WRITE_VERIFY_12: case WRITE_VERIFY_16: - return scsi_req_alloc(&scsi_disk_reqops, &s->qdev, tag, lun, - hba_private); + /* MMC writing cannot be done via pread/pwrite, because it sometimes + * involves writing beyond the maximum LBA or to negative LBA (lead-in). + * And once you do these writes, reading from the block device is + * unreliable, too. It is even possible that reads deliver random data + * from the host page cache (this is probably a Linux bug). + * + * We might use scsi_disk_reqops as long as no writing commands are + * seen, but performance usually isn't paramount on optical media. So, + * just make scsi-block operate the same as scsi-generic for them. + */ + if (s->qdev.type != TYPE_ROM) { + return scsi_req_alloc(&scsi_disk_reqops, &s->qdev, tag, lun, + hba_private); + } } return scsi_req_alloc(&scsi_generic_req_ops, &s->qdev, tag, lun, -- 1.7.7.1