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Re: [Qemu-trivial] [PATCH 2/2] qemu-img: better error message when openi

From: Maxim Levitsky
Subject: Re: [Qemu-trivial] [PATCH 2/2] qemu-img: better error message when opening a backing file fails
Date: Mon, 22 Jul 2019 12:46:24 +0300

On Mon, 2019-07-22 at 11:41 +0200, Kevin Wolf wrote:
> Am 21.07.2019 um 20:15 hat Maxim Levitsky geschrieben:
> > Currently we print message like that:
> > 
> > "
> > new_file.qcow2 : error message
> > "
> > 
> > However the error could have come from opening the backing file (e.g when 
> > it missing encryption keys),
> > thus try to clarify this by using this format:
> > 
> > "
> > qemu-img: error creating new_file.qcow2: base_file.qcow2: error message
> > Could not open backing image to determine size.
> > "
> The old error message was just unspecific. Your new error message can be
> actively misleading because you just unconditionally print the filename
> of the direct backing file, even though the error could have occurred
> while opening the backing file of the backing file (or even further down
> the backing chain).
> It's a common problem we have with backing files and error messages: We
> either don't print the filename where the error actually happened (like
> in this case), or we print all of the backing files in the chain (such
> as "Could not open top.qcow2: Could not open mid.qcow2: Could not open
> base.qcow2: Invalid something").
> Ideally, we'd find a way to print only the backing filename in such
> cases ("Could not open base.qcow2: Invalid something"). I'd gladly
> accept a patch that fixes error messages in this way for both open and
> create, but I'm afraid that your approach in this patch is too
> simplistic and not an improvement

You raise a very good point, I didn't thought about this.

Best regards,
        Maxim Levitsky

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