Re: [PATCH 01/10] vhost-user-blk: reconnect on any error during realize

[Roman Kagan]

On Thu, Nov 11, 2021 at 06:52:30PM +0100, Kevin Wolf wrote:
> Am 11.11.2021 um 16:33 hat Roman Kagan geschrieben:
> > vhost-user-blk realize only attempts to reconnect if the previous
> > connection attempt failed on "a problem with the connection and not an
> > error related to the content (which would fail again the same way in the
> > next attempt)".
> > 
> > However this distinction is very subtle, and may be inadvertently broken
> > if the code changes somewhere deep down the stack and a new error gets
> > propagated up to here.
> > 
> > OTOH now that the number of reconnection attempts is limited it seems
> > harmless to try reconnecting on any error.
> > 
> > So relax the condition of whether to retry connecting to check for any
> > error.
> > 
> > This patch amends a527e312b5 "vhost-user-blk: Implement reconnection
> > during realize".
> > 
> > Signed-off-by: Roman Kagan <rvkagan@yandex-team.ru>
> 
> It results in less than perfect error messages. With a modified export
> that just crashes qemu-storage-daemon during get_features, I get:
> 
> qemu-system-x86_64: -device vhost-user-blk-pci,chardev=c: Failed to read msg 
> header. Read 0 instead of 12. Original request 1.
> qemu-system-x86_64: -device vhost-user-blk-pci,chardev=c: Reconnecting after 
> error: vhost_backend_init failed: Protocol error
> qemu-system-x86_64: -device vhost-user-blk-pci,chardev=c: Reconnecting after 
> error: Failed to connect to '/tmp/vsock': Connection refused
> qemu-system-x86_64: -device vhost-user-blk-pci,chardev=c: Reconnecting after 
> error: Failed to connect to '/tmp/vsock': Connection refused
> qemu-system-x86_64: -device vhost-user-blk-pci,chardev=c: Failed to connect 
> to '/tmp/vsock': Connection refused

This patch doesn't change any error messages.  Which ones specifically
became less than perfect as a result of this patch?

> I guess this might be tolerable. On the other hand, the patch doesn't
> really fix anything either, but just gets rid of possible subtleties.

The remaining patches in the series make other errors beside -EPROTO
propagate up to this point, and some (most) of them are retryable.  This
was the reason to include this patch at the beginning of the series (I
guess I should've mentioned that in the patch log).

Thanks,
Roman.