Re: [Libguestfs] nbdkit error: "write reply: NBD_CMD_WRITE: Broken pipe"

On May 02 2022, Laszlo Ersek <lersek(a)redhat.com&gt; 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