[Xen-devel] use O_DIRECT to open disk images for IDE failed under xen-4.1.2 and qemu upstream

["Gonglei (Arei)" <arei.gonglei@xxxxxxxxxx>]

Hi, all

I use O_DIRECT to open disk images for IDE, but I'm failed. After debug, I get 
the below logs:
[2013-05-22 23:25:46] ide: CMD=c8
[2013-05-22 23:25:46] bmdma: readb 0x00 : 0x08
[2013-05-22 23:25:46] bmdma: writeb 0x00 : 0x09
[2013-05-22 23:25:46] bmdma_cmd_writeb: 0x00000009
[2013-05-22 23:25:46] bmdma: readb 0x02 : 0x01
[2013-05-22 23:25:46] bmdma: readb 0x02 : 0x01
[2013-05-22 23:25:46] bmdma: readb 0x02 : 0x01
[2013-05-22 23:25:46] bmdma: readb 0x02 : 0x01
[2013-05-22 23:25:46] bmdma: readb 0x02 : 0x01
[2013-05-22 23:25:46] bmdma: readb 0x02 : 0x01
[2013-05-22 23:26:39] bmdma: writeb 0x00 : 0x08
[2013-05-22 23:26:39] bmdma_cmd_writeb: 0x00000008
[2013-05-22 23:26:56] ====== offset:0 buf:0x7ff100f21c00 count:512 aio_offset:0
[2013-05-22 23:31:30] ====== offset:0 buf:0x7ff100f21c00 count:512 aio_offset:0
[2013-05-22 23:31:30] ====== handle_aiocb_rw_linear errno: -14
[2013-05-22 23:31:30] ====== paio_complete errno=14
[2013-05-22 23:31:30] ====== ide_dma_error!!!
[2013-05-22 23:31:30] ide: read status addr=0x3f6 val=41

QEMU command line :
qemu-system-i386 -xen-domid 837 -chardev 
socket,id=libxl-cmd,path=/var/run/xen/qmp-libxl-837,server,nowait -mon 
chardev=libxl-cmd,mode=control -name suse11 -vnc 0.0.0.0:1 -serial pty -boot 
order=c -usb -usbdevice tablet -smp 2,maxcpus=2 -device 
rtl8139,id=nic0,netdev=net0,mac=00:16:3e:13:d3:72 -netdev 
type=tap,id=net0,ifname=tap837.0,downscript=no -M xenfv -m 2040 -drive 
file=/mnt/sdd/image/suse.image,if=ide,index=0,media=disk,format=raw,cache=none

errno 14 shows Bad Address. And I find QEMU_AIO_MISALIGNED flag bit is not set 
through debug. 

    /*
     * If O_DIRECT is used the buffer needs to be aligned on a sector
     * boundary.  Check if this is the case or tell the low-level
     * driver that it needs to copy the buffer.
     */
    if ((bs->open_flags & BDRV_O_NOCACHE)) {
        if (!bdrv_qiov_is_aligned(bs, qiov)) {    //if the address is 
aligned-512, will no meet the conditions
            type |= QEMU_AIO_MISALIGNED;
#ifdef CONFIG_LINUX_AIO
        } else if (s->use_aio) {
            return laio_submit(bs, s->aio_ctx, s->fd, sector_num, qiov,
                               nb_sectors, cb, opaque, type);
#endif

Next process:
static ssize_t handle_aiocb_rw(struct qemu_paiocb *aiocb)
{
    ssize_t nbytes;
    char *buf;

    if (!(aiocb->aio_type & QEMU_AIO_MISALIGNED)) {
        /*
         * If there is just a single buffer, and it is properly aligned
         * we can just use plain pread/pwrite without any problems.
         */
        if (aiocb->aio_niov == 1)
             return handle_aiocb_rw_linear(aiocb, aiocb->aio_iov->iov_base); 
//this way, and reports errno 14 next

Anyone have a good method to resolve this bug? Thanks!

Best Regards!
-Gonglei

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