Re: [Qemu-devel] [PATCH 2/2] block/rbd: Attempt to parse legacy filenames

[Jeff Cody <jcody@redhat.com>]

On Tue, Sep 11, 2018 at 01:03:44PM -0500, Eric Blake wrote:
> On 9/11/18 12:15 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).
> 
> No one should be mixing new and old, though.
> 
> >
> >Signed-off-by: Jeff Cody <jcody@redhat.com>
> >---
> >  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;
> 
> Oh, my comment about simplifying this in 1/2 is probably moot, now that you
> are doing a lot more based on local_err rather than just blindly propagating
> it.
> 
> >+        /* 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 */
> >+        Error *parse_err = NULL;
> >+
> >+        filename = g_strdup(qdict_get_try_str(options, "filename"));
> 
> You already spotted your leak.
> 
> >+        qdict_del(options, "filename");
> >+
> >+        qemu_rbd_parse_filename(filename, options, NULL);
> >+
> >+        g_free(keypairs);
> 
> Wait. Why are you unilaterally freeing any previously-parsed keypairs in
> favor of the ones parsed out of the filename?  I'd rather that we insist on
> only old behavior, or only new, and not some mix.  Thus, if we already
> detected keypairs at all, we should declare this situation as an error,
> rather than throwing them away.
> 

Good point.  I'll flag (local_err && keypairs) as an error.

I also just realized I need to check for NULL filename, and error out as
well in that case.

> >+        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;
> >+        }
> >      }
> 
> The idea of trying two parses makes sense, but I'm hoping v2 better handles
> the case of detecting bad attempts to mix-and-match behavior. Furthermore,
> is there an iotests that you can modify (or add) as a regression test for
> this working the way we want?

Hmm... yes, that should be doable.  I'm not sure if I can do it without the
'success' path being a timeout when there is no ceph server present, though.
I'll see what I can do.

-Jeff