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

[Eric Blake]

On 4/2/20 4:40 AM, Richard W.M. Jones wrote:

>> with your suggestion, we'd have:
>>
>> initial try fails:
>>   retry 1: original error
>> delay
>> retry 1 fails:
>>   retry 2: original error
>> delay
>> retry 2 fails:
>>   could not recover after 2 retries
>>
>> where we lost the log of the errno of retry 2.
> 
> It's not printed, but also it's not lost.  do_retry will immediately
> return false, causing the called function to return this final errno
> (hopefully back to the client).  The reason for printing the "original
> errno" was because those intermediate errnos would otherwise be lost.

Good point.

> 
> Attached is my suggested patch - it's a small evolution on top of
> yours.  The output is now:
> 
> $ rm -f /tmp/inject ; (sleep 5s; touch /tmp/inject ) & ./nbdkit -f -v -U - null size=1G --filter=retry --filter=noextents --filter=error error-rate=100% error-file=/tmp/inject --filter=delay rdelay=1 retries=3 --run 'qemu-img convert $nbd /var/tmp/out.img'
> 
> nbdkit: null[1]: error: injecting EIO error into pread
> nbdkit: null[1]: debug: pread failed: original errno = 5
> nbdkit: null[1]: debug: retry 1: waiting 2 seconds before retrying
> 
> nbdkit: null[1]: error: injecting EIO error into pread
> nbdkit: null[1]: debug: pread failed: original errno = 5
> nbdkit: null[1]: debug: retry 2: waiting 4 seconds before retrying
> 
> nbdkit: null[1]: error: injecting EIO error into pread
> nbdkit: null[1]: debug: pread failed: original errno = 5
> nbdkit: null[1]: debug: retry 3: waiting 8 seconds before retrying
> 
> nbdkit: null[1]: error: injecting EIO error into pread
> nbdkit: null[1]: debug: could not recover after 3 retries
> nbdkit: null[1]: debug: sending error reply: Input/output error
> 

Yes, this is looking better.  Let's go for it.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org