Hi Paul,
On Tue, Oct 1, 2013 at 10:27 PM, Paul Clements <[email protected]>wrote:
> Hi,
>
> On Tue, Oct 1, 2013 at 9:27 AM, Raphael Bauduin <[email protected]> wrote:
>
>>
>> How can I determine which is the first free nbd device?
>>
>
> By free do you mean not connected?
>
yes
>
>
>> Currently I have 2 ways to check if an device is connected: the first is
>> calling file on the device and check if it is empty or not. The second is
>> call lsblk and see if the device is in the list.
>>
>
> Neither of these distinguishes between connected and non-connected...
>
These two ways worked in my case as I only mount disk images with qemu-nbd
but I'll switch to a reliable way to detect connected devices.
Thanks!
Raph
>
>
>>
>> Rather than looping over all nbd devices until I find one free to use, I
>> wondered if there's a way to immediately get the first free nbd device.
>>
>
> Not directly, that I know of, but there are two ways to determine which
> nbds are connected or not:
>
> /proc/partitions lists only active nbds:
>
> debian-i386~$ cat /proc/partitions
> major minor #blocks name
>
> 7 1 409600 loop1
> 7 5 2560000 loop5
> 8 0 16777216 sda
> 8 1 16043008 sda1
> 8 2 1 sda2
> 8 5 731136 sda5
> 11 0 1048575 sr0
> 9 1 409588 md1
> 43 5 2560000 nbd5
>
> Also, the sysfs pid file is only present when the nbd is connected (i.e.,
> an nbd-client is running):
>
> debian-i386~$ cat /sys/block/nbd5/pid
> 18172
>
> debian-i386~$ ls -l /sys/block/nbd0/pid
> ls: cannot access /sys/block/nbd0/pid: No such file or directory
>
> --
> Paul
>
>
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