[Libguestfs] [nbdkit PATCH] retry: Tweak error message

[Richard W.M. Jones]

On Tue, Mar 31, 2020 at 04:00:22PM -0500, Eric Blake wrote:
> The retry filter defaults to 5 retries, but when run with verbose
> details produces some confusing output:
> 
> $ rm -f /tmp/inject; (sleep 5s; touch /tmp/inject)& ./nbdkit -f -v -U - \
>   null 1G --filter=retry --filter=noextents --filter=error error-rate=100% \
>   error-file=/tmp/inject --filter=delay rdelay=1 \
>   --run 'qemu-img convert $nbd out.img'
> ...
> nbdkit: null[1]: debug: noextents: pread count=2097152 offset=14680064
> nbdkit: null[1]: debug: error: pread count=2097152 offset=14680064
> nbdkit: null[1]: error: injecting EIO error into pread
> nbdkit: null[1]: debug: retry 6: original errno = 5
> nbdkit: null[1]: debug: could not recover after 5 retries
> 
> The code is correct (there were six attempts, but that corresponds to
> 5 retries after the initial attempt; comments mention that retry=0
> turns the filter into a no-op but even that requires an initial
> attempt).  So all we need to adjust is the output.
> 
> Fixes: f0f0ec49
> Signed-off-by: Eric Blake <eblake at redhat.com>
> ---
> 
> I'm pushing this in response to https://bugzilla.redhat.com/1819240
> At the same time, I'm looking at whether qemu-img should be tweaked
> to have a mode where it gives up on the first EIO error, rather than
> plowing on through the rest of the image even after the first error.
> 
>  filters/retry/retry.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/filters/retry/retry.c b/filters/retry/retry.c
> index 11e5313b..db91d7ca 100644
> --- a/filters/retry/retry.c
> +++ b/filters/retry/retry.c
> @@ -173,7 +173,7 @@ do_retry (struct retry_handle *h,
> 
>   again:
>    /* Log the original errno since it will be lost when we retry. */
> -  nbdkit_debug ("retry %d: original errno = %d", data->retry+1, *err);
> +  nbdkit_debug ("retry attempt %d: original errno = %d", data->retry, *err);
> 
>    if (data->retry >= retries) {
>      nbdkit_debug ("could not recover after %d retries", retries);

I think adding 1 was correct, so that the retries count from 1.

How about moving the message to make it conditional instead,
like this?

again:
  /* Log the original errno since it will be lost when we retry. */
  if (data->retry < retries)
    nbdkit_debug ("retry %d: original errno = %d", data->retry+1, *err);
  else {
     nbdkit_debug ("could not recover after %d retries", retries);
  ...

Rich.

-- 
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