Re: How to safely disconnect NBD device

["Nikolaus Rath" <Nikolaus@rath.org>]

Hi Paul, 

Would you be able to help with the question below? I've been told that you're the current maintainer of the NBD kernel code..

On Fri, 6 May 2022, at 21:25, Nikolaus Rath wrote:
> $ nbd-client localhost /dev/nbd1 && mkfs.ext4 /dev/nbd1 && nbd-client -d
> /dev/nbd1
>
> Frequently gives me errors like this:
>
> May 02 15:20:50 vostro.rath.org kernel: nbd1: detected capacity change 
> from 0 to 52428800
> May 02 15:20:50 vostro.rath.org kernel: block nbd1: NBD_DISCONNECT
> May 02 15:20:50 vostro.rath.org kernel: block nbd1: Disconnected due to 
> user request.
> May 02 15:20:50 vostro.rath.org kernel: block nbd1: shutting down 
> sockets
> May 02 15:20:50 vostro.rath.org kernel: I/O error, dev nbd1, sector 776 
> op 0x0:(READ) flags 0x80700 phys_seg 29 prio class 0
> May 02 15:20:50 vostro.rath.org kernel: I/O error, dev nbd1, sector 776 
> op 0x0:(READ) flags 0x0 phys_seg 1 prio class 0
> May 02 15:20:50 vostro.rath.org kernel: Buffer I/O error on dev nbd1, 
> logical block 97, async page read
> May 02 15:20:50 vostro.rath.org kernel: block nbd1: Attempted send on 
> invalid socket
> May 02 15:20:50 vostro.rath.org kernel: I/O error, dev nbd1, sector 0 
> op 0x1:(WRITE) flags 0x800 phys_seg 0 prio class 0
> May 02 15:20:50 vostro.rath.org kernel: block nbd1: Attempted send on 
> invalid socket
> May 02 15:20:50 vostro.rath.org kernel: I/O error, dev nbd1, sector 0 
> op 0x1:(WRITE) flags 0x800 phys_seg 0 prio class 0
>
> To me, this looks as if the kernel is shutting down the NBD connection
> while there are still active requests and/or while there is still dirty
> data that needs to be flushed.
>
> Is this expected behavior?
>
> If so, what is the recommended way to *safely* disconnect an NBD device?


Best,
-Nikolaus

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