Re: BD-RE mount problem

On 10/08/12 10:33 AM, Thomas Schmitt wrote:
> Hi,
>
> i can reproduce the symptoms by a read-only situation of drive and
> media. (It should not happen with BD-RE in a BD writer, of course.)
>
> open_sr0.c with O_NDELAY yielded:
>> open: fd= 3 , errno= 0
>> write: ret= 2048 , errno= 0
> I get the same behavior when i put a DVD into a DVD-ROM drive.
> It allows me to dump my data into a black hole and reports no error
> to the userspace program.
> In /var/log/messages i find
>
>    sr 6:0:0:0: [sr1] Result: hostbyte=DID_OK driverbyte=DRIVER_SENSE
>    sr 6:0:0:0: [sr1] Sense Key : Illegal Request [current]
>    sr 6:0:0:0: [sr1] Add. Sense: Invalid command operation code
>    sr 6:0:0:0: [sr1] CDB: Write(10): 2a 00 00 00 00 00 00 00 01 00
>    lost page write due to I/O error on sr1
>
> Looks like an old kernel bug resp. unwanted way to silently
> shoot your own foot.
> It happens too with 8 subsequent write() calls with sleep(1) inbetween.
> No delayed error is returned.
>
>
> -------------------------------------------------------------------
>
> I dug out the reason why libburn (underneath xorriso) uses O_NDELAY
> when it opens the drive device file.
>
> A note to myself in libburn/sg-linux.c:
>
>             O_NONBLOCK is prescribed by<linux/cdrom.h>
>             Switched to O_NDELAY for LKML statement 2007/4/11/141 by Alan Cox:
>             "open() has side effects. The CD layer allows you to open
>              with O_NDELAY if you want to avoid them."
>
> In Debian squeeze's /usr/include/linux/cdrom.h:
>
>   * Additionally, as of Linux 2.1.x, all Linux application programs
>   * should use the O_NONBLOCK option when opening a CD-ROM device
>   * for subsequent ioctl commands.  This allows for neat system errors
>   * like "No medium found" or "Wrong medium type" upon attempting to
>   * mount or play an empty slot, mount an audio disc, or play a data disc.
>
> This explains why open() does not fail with O_NDELAY (= O_NOBLOCK):
> For ioctl(SG_IO) one needs w-permission. So it must tolerate
>    O_RDWR | O_NDELAY
> But why does not write(2) fail afterwards ?
>
>
> Have a nice day :)
>
> Thomas
I did try this when booting from System Rescue CD (sub stick) as well. I 
get the same results. I'm hoping to get another system up and running 
next week that also has a BluRay writer. I'll give that a try too.

Thanks.


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