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Re: [Qemu-devel] use O_DIRECT to open disk images for IDE failed under x


From: Gonglei (Arei)
Subject: Re: [Qemu-devel] use O_DIRECT to open disk images for IDE failed under xen-4.1.2 and qemu upstream
Date: Fri, 24 May 2013 02:59:05 +0000

Hi,

> 
> 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.

A few days ago, I asked a question about the IDE FLUSH time of guest´╝Ü 
http://lists.nongnu.org/archive/html/qemu-devel/2013-05/msg02642.html

finally I found that because Qemu use write-back flag to open disk images by 
default. 
so I hope to use O_DIRECT to avoid meeting that problem, but I'm failed under 
Xen platform with Qemu upstream.

-Gonglei

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