Re: [Libguestfs] nbdkit error: "write reply: NBD_CMD_WRITE: Broken pipe"
On May 02 2022, Laszlo Ersek <lersek(a)redhat.com> wrote:
On 05/01/22 18:35, Nikolaus Rath wrote:
> Hi,
>
> I am developing a new nbdkit plugin, and occasionally I am getting
> errors like this:
>
> |nbdkit: s3backer.8: error: write reply: NBD_CMD_WRITE: Broken pipe
> nbdkit: s3backer.15: error: write reply: NBD_CMD_WRITE: Broken pipe|
>
>
> (where "s3backer" is the plugin name).
>
> I am not sure what to make of these. Can someone advise?
>
> Looking at the nbdkit source, it looks to me like these are generated
> when there is a problem sending a reply to the nbd client. On the other
> hand, I am using the standard 'nbd-client' program through a Unix
> socket, so I'd think this should not result in errors...?
If your plugin managed to crash nbd-client remotely, that would be
consistent with this symptom.
So I tried to reproduce this, and noticed something odd. It seems I can
disconnect the nbd device (nbd-client -d) while there are still requests
in flight:
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
This was generated by running:
$ nbd-client localhost /dev/nbd1 && mkfs.ext4 /dev/nbd1 && nbd-client -d
/dev/nbd1
Is that expected behavior?
I would have thought that nb-client will block until any dirty data has
been written.
Curiously enough, in this case I did *not* get the above warnings from
nbdkit itself.
Best,
-Nikolaus
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