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Re: [Qemu-devel] [PATCH RFC 1/1] block: Handle NULL options correctly in


From: Dong Jia Shi
Subject: Re: [Qemu-devel] [PATCH RFC 1/1] block: Handle NULL options correctly in raw_open
Date: Tue, 14 Mar 2017 11:23:12 +0800
User-agent: Mutt/1.7.0 (2016-08-17)

* Kevin Wolf <address@hidden> [2017-03-13 11:15:22 +0100]:

> Am 13.03.2017 um 04:31 hat Dong Jia Shi geschrieben:
> > * Dong Jia Shi <address@hidden> [2017-03-08 17:31:05 +0800]:
> > 
> > > * Kevin Wolf <address@hidden> [2017-03-08 10:13:46 +0100]:
> > > 
> > > > Am 08.03.2017 um 03:15 hat Dong Jia Shi geschrieben:
> > > > > A normal call for raw_open should always pass in a non-NULL @options,
> > > > > but for some certain cases (e.g. trying to applying snapshot on a RBD
> > > > > image), they call raw_open with a NULL @options right after the 
> > > > > calling
> > > > > for raw_close.
> > > > > 
> > > > > Let's take the NULL @options as a sign of trying to do raw_open again,
> > > > > and just simply return a success code.
> > > > > 
> > > > > Signed-off-by: Dong Jia Shi <address@hidden>
> > > > 
> > > > I think we rather need to fix bdrv_snapshot_goto() so that it doesn't
> > > > pass NULL, but the actual options that were given for the node (i.e.
> > > > bs->options).
> > > I've tried that before the current try. bs->options does not have the
> > > "file" key-value pair, so that leads to a fail too. Should we put "file"
> > > in to the options manually? I noticed that it was removed from
> > > bs->options during the calling of bdrv_open_inherit.
> > > 
> > Hi Kevin,
> > 
> > After thinking for quite some time, I still don't think we need to fix
> > the caller. The reason is that raw_close always does nothing, so no
> > matter what the caller passing in, raw_open should do nothing but just
> > return 0.
> 
> raw is not the only format driver in qemu.
> 
Hi Kevin,

Before this I assumed that the long existing code in bdrv_snapshot_goto
which passes in a NULL options to raw_open is on purpose, and that
implies to me raw_open (and any other .bdrv_open callback) takes the
responsibility to handle NULL options well. So at a first glance, I read
your above comment as:
"You should also fix .bdrv_open callback for every other formats to
handle NULL options as well."

But after staring it for a while, I read it from another point around:
"You should fix the caller."
If this is what you actually meant to tell, I have the following
proposal then:
diff --git a/block/snapshot.c b/block/snapshot.c
index bf5c2ca..dfec139 100644
--- a/block/snapshot.c
+++ b/block/snapshot.c
@@ -27,6 +27,7 @@
 #include "block/block_int.h"
 #include "qapi/error.h"
 #include "qapi/qmp/qerror.h"
+#include "qapi/qmp/qstring.h"
 
 QemuOptsList internal_snapshot_opts = {
     .name = "snapshot",
@@ -189,9 +190,14 @@ int bdrv_snapshot_goto(BlockDriverState *bs,
     }
 
     if (bs->file) {
+        QDict *options = qdict_clone_shallow(bs->options);
+        qdict_put(options, "file",
+                  qstring_from_str(bdrv_get_node_name(bs->file->bs)));
+
         drv->bdrv_close(bs);
         ret = bdrv_snapshot_goto(bs->file->bs, snapshot_id);
-        open_ret = drv->bdrv_open(bs, NULL, bs->open_flags, NULL);
+        open_ret = drv->bdrv_open(bs, options, bs->open_flags, NULL);
+        QDECREF(options);
         if (open_ret < 0) {
             bdrv_unref(bs->file->bs);
             bs->drv = NULL;

I know I'm a little wordy, but that's because I want to make things
clear. Anyway, I have to rely on your advice on this, since you are the
expert.

> Kevin
> 

-- 
Dong Jia




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