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Re: [Qemu-stable] [Qemu-devel] [PATCH 2/2] block/rbd: Attempt to parse l
From: |
Jeff Cody |
Subject: |
Re: [Qemu-stable] [Qemu-devel] [PATCH 2/2] block/rbd: Attempt to parse legacy filenames |
Date: |
Tue, 11 Sep 2018 14:37:00 -0400 |
User-agent: |
Mutt/1.5.24 (2015-08-30) |
On Tue, Sep 11, 2018 at 02:22:31PM -0400, John Snow wrote:
>
>
> On 09/11/2018 01:15 AM, Jeff Cody wrote:
> > When we converted rbd to get rid of the older key/value-centric
> > encoding format, we broke compatibility with image files with backing
> > file strings encoded in the old format.
> >
> > This leaves a bit of an ugly conundrum, and a hacky solution.
> >
> > If the initial attempt to parse the "proper" options fails, it assumes
> > that we may have an older key/value encoded filename. Fall back to
> > attempting to parse the filename, and extract the required options from
> > it. If that fails, pass along the original error message.
> >
> > This approach has a potential drawback: if for some reason there are
> > some options supplied the new way, and some the old way, we may not
> > catch all the old options if they are not required options (since it
> > won't cause the initial failure).
> >
> > Signed-off-by: Jeff Cody <address@hidden>
> > ---
> > block/rbd.c | 30 +++++++++++++++++++++++++++---
> > 1 file changed, 27 insertions(+), 3 deletions(-)
> >
> > diff --git a/block/rbd.c b/block/rbd.c
> > index a8e79d01d2..bce86b8bde 100644
> > --- a/block/rbd.c
> > +++ b/block/rbd.c
> > @@ -685,7 +685,7 @@ static int qemu_rbd_open(BlockDriverState *bs, QDict
> > *options, int flags,
> > BlockdevOptionsRbd *opts = NULL;
> > const QDictEntry *e;
> > Error *local_err = NULL;
> > - char *keypairs, *secretid;
> > + char *keypairs, *secretid, *filename;
> > int r;
> >
> > keypairs = g_strdup(qdict_get_try_str(options, "=keyvalue-pairs"));
> > @@ -700,8 +700,32 @@ static int qemu_rbd_open(BlockDriverState *bs, QDict
> > *options, int flags,
> >
> > r = qemu_rbd_convert_options(bs, options, &opts, &local_err);
> > if (local_err) {
> > - error_propagate(errp, local_err);
> > - goto out;
> > + /* If the initial attempt to convert and process the options
> > failed,
> > + * we may be attempting to open an image file that has the rbd
> > options
> > + * specified in the older format consisting of all key/value pairs
> > + * encoded in the filename. Go ahead and attempt to parse the
> > + * filename, and see if we can pull out the required options */
>
> Is it worth splitting out the legacy parsing routine here into its own
> function, given that we will generally depend on it not being invoked?
> i.e., for readability, it doesn't need to distract us.
>
Yeah, that would probably be good.
> > + Error *parse_err = NULL;
> > +
> > + filename = g_strdup(qdict_get_try_str(options, "filename"));
> > + qdict_del(options, "filename");
> > +
> > + qemu_rbd_parse_filename(filename, options, NULL);
> > +
> > + g_free(keypairs);
>
> As Eric already noticed, better to just return with error if this is
> already set.
>
> > + keypairs = g_strdup(qdict_get_try_str(options, "=keyvalue-pairs"));
> > + if (keypairs) {
> > + qdict_del(options, "=keyvalue-pairs");
> > + }
> > +
> > + r = qemu_rbd_convert_options(bs, options, &opts, &parse_err);
> > + if (parse_err) {
> > + /* if the second attempt failed, pass along the original error
> > + * message for the current format */
> > + error_propagate(errp, local_err);
> > + error_free(parse_err);
> > + goto out;
> > + }
>
> If it does succeed, though, ought we emit a deprecated warning that the
> old specification syntax is not supported?
>
I don't know. Without this support, we can't open some existing images. At
what point would we actually remove that support?
> Once we load the image, will the header get rewritten into a compliant
> format?
>
Hmm - I think in some code paths, but not all. I don't think the answer is
'yes' universally, alas.
[Qemu-stable] [PATCH 1/2] block/rbd: pull out qemu_rbd_convert_options, Jeff Cody, 2018/09/11