diff mbox

[17/20] qemu-io: Use bdrv_parse_cache_mode() in reopen_f()

Message ID 1458325289-17848-18-git-send-email-kwolf@redhat.com
State New
Headers show

Commit Message

Kevin Wolf March 18, 2016, 6:21 p.m. UTC
We must forbid changing the WCE flag in bdrv_reopen() in the same patch,
as otherwise the behaviour would change so that the flag takes
precedence over the explicitly specified option.

The correct value of the WCE flag depends on the BlockBackend user (e.g.
guest device) and isn't a decision that the QMP client makes, so this
change is what we want.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---
 block.c                    | 18 ++++++------------
 qemu-io-cmds.c             | 14 +++++++++++++-
 tests/qemu-iotests/142     |  2 +-
 tests/qemu-iotests/142.out |  2 +-
 4 files changed, 21 insertions(+), 15 deletions(-)

Comments

Max Reitz March 26, 2016, 9:05 p.m. UTC | #1
On 18.03.2016 19:21, Kevin Wolf wrote:
> We must forbid changing the WCE flag in bdrv_reopen() in the same patch,
> as otherwise the behaviour would change so that the flag takes
> precedence over the explicitly specified option.
> 
> The correct value of the WCE flag depends on the BlockBackend user (e.g.
> guest device) and isn't a decision that the QMP client makes, so this
> change is what we want.
> 
> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> ---
>  block.c                    | 18 ++++++------------
>  qemu-io-cmds.c             | 14 +++++++++++++-
>  tests/qemu-iotests/142     |  2 +-
>  tests/qemu-iotests/142.out |  2 +-
>  4 files changed, 21 insertions(+), 15 deletions(-)
> 

[...]

> diff --git a/qemu-io-cmds.c b/qemu-io-cmds.c
> index e929d24..7de3754 100644
> --- a/qemu-io-cmds.c
> +++ b/qemu-io-cmds.c

[...]

> @@ -2136,14 +2137,25 @@ static int reopen_f(BlockBackend *blk, int argc, char **argv)
>          return qemuio_command_usage(&reopen_cmd);
>      }
>  
> +    if (writethrough != blk_enable_write_cache(blk) &&
> +        blk_get_attached_dev(blk))
> +    {
> +        error_report("Cannot change cache.writeback: Device attached");
> +        qemu_opts_reset(&reopen_opts);
> +        return 0;
> +    }
> +
>      qopts = qemu_opts_find(&reopen_opts, NULL);
>      opts = qopts ? qemu_opts_to_qdict(qopts, NULL) : NULL;
>      qemu_opts_reset(&reopen_opts);
>  
> +    flags |= blk_enable_write_cache(blk) ? BDRV_O_CACHE_WB : 0;

Shouldn't this be bdrv_enable_write_cache(bs)?

With blk_enable_write_cache(blk), reopening a non-WB BB should always
fail because bdrv_reopen_multiple() accuses us of trying to change the
WB mode (whereas we really don't want to change the BDS's mode).

Max

>      brq = bdrv_reopen_queue(NULL, bs, opts, flags);
>      bdrv_reopen_multiple(brq, &local_err);
>      if (local_err) {
>          error_report_err(local_err);
> +    } else {
> +        blk_set_enable_write_cache(blk, !writethrough);
>      }
>  
>      return 0;
Kevin Wolf March 29, 2016, 10:16 a.m. UTC | #2
Am 26.03.2016 um 22:05 hat Max Reitz geschrieben:
> On 18.03.2016 19:21, Kevin Wolf wrote:
> > We must forbid changing the WCE flag in bdrv_reopen() in the same patch,
> > as otherwise the behaviour would change so that the flag takes
> > precedence over the explicitly specified option.
> > 
> > The correct value of the WCE flag depends on the BlockBackend user (e.g.
> > guest device) and isn't a decision that the QMP client makes, so this
> > change is what we want.
> > 
> > Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> > ---
> >  block.c                    | 18 ++++++------------
> >  qemu-io-cmds.c             | 14 +++++++++++++-
> >  tests/qemu-iotests/142     |  2 +-
> >  tests/qemu-iotests/142.out |  2 +-
> >  4 files changed, 21 insertions(+), 15 deletions(-)
> > 
> 
> [...]
> 
> > diff --git a/qemu-io-cmds.c b/qemu-io-cmds.c
> > index e929d24..7de3754 100644
> > --- a/qemu-io-cmds.c
> > +++ b/qemu-io-cmds.c
> 
> [...]
> 
> > @@ -2136,14 +2137,25 @@ static int reopen_f(BlockBackend *blk, int argc, char **argv)
> >          return qemuio_command_usage(&reopen_cmd);
> >      }
> >  
> > +    if (writethrough != blk_enable_write_cache(blk) &&
> > +        blk_get_attached_dev(blk))
> > +    {
> > +        error_report("Cannot change cache.writeback: Device attached");
> > +        qemu_opts_reset(&reopen_opts);
> > +        return 0;
> > +    }
> > +
> >      qopts = qemu_opts_find(&reopen_opts, NULL);
> >      opts = qopts ? qemu_opts_to_qdict(qopts, NULL) : NULL;
> >      qemu_opts_reset(&reopen_opts);
> >  
> > +    flags |= blk_enable_write_cache(blk) ? BDRV_O_CACHE_WB : 0;
> 
> Shouldn't this be bdrv_enable_write_cache(bs)?
> 
> With blk_enable_write_cache(blk), reopening a non-WB BB should always
> fail because bdrv_reopen_multiple() accuses us of trying to change the
> WB mode (whereas we really don't want to change the BDS's mode).

bdrv_enable_write_cache() is only a wrapper around
blk_enable_write_cache(), so that wouldn't make any difference. It also
means that bdrv_reopen() checks the cache mode of the BlockBackend
rather than always returning true. This line exists precisely to avoid
the error message you mention.

And as you noticed, the line goes away anyway when BDRV_O_CACHE_WB is
removed later in the series.

Kevin
diff mbox

Patch

diff --git a/block.c b/block.c
index 4e95d01..3775e65 100644
--- a/block.c
+++ b/block.c
@@ -2028,18 +2028,12 @@  int bdrv_reopen_prepare(BDRVReopenState *reopen_state, BlockReopenQueue *queue,
 
     update_flags_from_options(&reopen_state->flags, opts);
 
-    /* If a guest device is attached, it owns WCE */
-    if (reopen_state->bs->blk && blk_get_attached_dev(reopen_state->bs->blk)) {
-        bool old_wce = bdrv_enable_write_cache(reopen_state->bs);
-        bool new_wce = (reopen_state->flags & BDRV_O_CACHE_WB);
-        if (old_wce != new_wce) {
-            error_setg(errp, "Cannot change cache.writeback: Device attached");
-            ret = -EINVAL;
-            goto error;
-        }
-    }
-    if (!reopen_state->bs->blk && !(reopen_state->flags & BDRV_O_CACHE_WB)) {
-        error_setg(errp, "Cannot disable cache.writeback: No BlockBackend");
+    /* WCE is a BlockBackend level option, can't change it */
+    bool old_wce = bdrv_enable_write_cache(reopen_state->bs);
+    bool new_wce = (reopen_state->flags & BDRV_O_CACHE_WB);
+
+    if (old_wce != new_wce) {
+        error_setg(errp, "Cannot change cache.writeback");
         ret = -EINVAL;
         goto error;
     }
diff --git a/qemu-io-cmds.c b/qemu-io-cmds.c
index e929d24..7de3754 100644
--- a/qemu-io-cmds.c
+++ b/qemu-io-cmds.c
@@ -2104,6 +2104,7 @@  static int reopen_f(BlockBackend *blk, int argc, char **argv)
     QDict *opts;
     int c;
     int flags = bs->open_flags;
+    bool writethrough = !blk_enable_write_cache(blk);
 
     BlockReopenQueue *brq;
     Error *local_err = NULL;
@@ -2111,7 +2112,7 @@  static int reopen_f(BlockBackend *blk, int argc, char **argv)
     while ((c = getopt(argc, argv, "c:o:r")) != -1) {
         switch (c) {
         case 'c':
-            if (bdrv_parse_cache_flags(optarg, &flags) < 0) {
+            if (bdrv_parse_cache_mode(optarg, &flags, &writethrough) < 0) {
                 error_report("Invalid cache option: %s", optarg);
                 return 0;
             }
@@ -2136,14 +2137,25 @@  static int reopen_f(BlockBackend *blk, int argc, char **argv)
         return qemuio_command_usage(&reopen_cmd);
     }
 
+    if (writethrough != blk_enable_write_cache(blk) &&
+        blk_get_attached_dev(blk))
+    {
+        error_report("Cannot change cache.writeback: Device attached");
+        qemu_opts_reset(&reopen_opts);
+        return 0;
+    }
+
     qopts = qemu_opts_find(&reopen_opts, NULL);
     opts = qopts ? qemu_opts_to_qdict(qopts, NULL) : NULL;
     qemu_opts_reset(&reopen_opts);
 
+    flags |= blk_enable_write_cache(blk) ? BDRV_O_CACHE_WB : 0;
     brq = bdrv_reopen_queue(NULL, bs, opts, flags);
     bdrv_reopen_multiple(brq, &local_err);
     if (local_err) {
         error_report_err(local_err);
+    } else {
+        blk_set_enable_write_cache(blk, !writethrough);
     }
 
     return 0;
diff --git a/tests/qemu-iotests/142 b/tests/qemu-iotests/142
index 8bbbfde..a035747 100755
--- a/tests/qemu-iotests/142
+++ b/tests/qemu-iotests/142
@@ -216,7 +216,7 @@  echo
 # BDS initialised with the json: pseudo-protocol, but still have it inherit
 # options from its parent node.
 
-hmp_cmds="qemu-io none0 \"reopen -o cache.writeback=off,cache.direct=on,cache.no-flush=on\"
+hmp_cmds="qemu-io none0 \"reopen -o cache.direct=on,cache.no-flush=on\"
 info block none0
 info block image
 info block blkdebug
diff --git a/tests/qemu-iotests/142.out b/tests/qemu-iotests/142.out
index c922490..3d5ef5f 100644
--- a/tests/qemu-iotests/142.out
+++ b/tests/qemu-iotests/142.out
@@ -414,7 +414,7 @@  cache.no-flush=on on backing-file
 
 --- Change cache mode in parent, child has explicit option in JSON ---
 
-    Cache mode:       writethrough, direct, ignore flushes
+    Cache mode:       writeback, direct, ignore flushes
     Cache mode:       writeback, direct, ignore flushes
     Cache mode:       writeback, direct, ignore flushes
     Cache mode:       writeback, ignore flushes