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

[Stefano Stabellini <stefano.stabellini@eu.citrix.com>]

On Thu, 23 May 2013, Gonglei (Arei) wrote:
> 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!
 
I know that this is not the answer you are looking for but why do you
want to use O_DIRECT with IDE?
It should be perfectly safe to use write-back.