Michael Roth <mdr...@linux.vnet.ibm.com> writes:
I don't think this is the most correct solution but I think it's good
enough in practice so
Reviewed-by: Anthony Liguori <aligu...@us.ibm.com>
Regards,
Anthony Liguori
> We currently hard-code property size at 4096 for the purposes of
> getattr()/stat()/etc. For 'state' properties we can exceed this easily,
> leading to truncated responses.
>
> Instead, for a particular property, make it
> max(4096, most_recent_property_size * 2). This allows some
> head-room for properties that change size periodically (numbers,
> strings, state properties containing arrays, etc)
>
> Also, implement a simple property cache to avoid spinning on qom-get
> if an application reads beyond the actual size. This also allows us
> to use a snapshot of a single qom-get that persists across read()'s.
> Old Cache entries are evicted as soon as we attempt to read() from
> offset 0 again.
>
> Signed-off-by: Michael Roth <mdr...@linux.vnet.ibm.com>
> ---
> QMP/qom-fuse | 24 +++++++++++++++++-------
> 1 file changed, 17 insertions(+), 7 deletions(-)
>
> diff --git a/QMP/qom-fuse b/QMP/qom-fuse
> index 5c6754a..bd43f29 100755
> --- a/QMP/qom-fuse
> +++ b/QMP/qom-fuse
> @@ -26,6 +26,7 @@ class QOMFS(Fuse):
> self.qmp.connect()
> self.ino_map = {}
> self.ino_count = 1
> + self.prop_cache = {}
>
> def get_ino(self, path):
> if self.ino_map.has_key(path):
> @@ -67,12 +68,16 @@ class QOMFS(Fuse):
> if not self.is_property(path):
> return -ENOENT
>
> - path, prop = path.rsplit('/', 1)
> - try:
> - data = str(self.qmp.command('qom-get', path=path, property=prop))
> - data += '\n' # make values shell friendly
> - except:
> - return -EPERM
> + # avoid extra calls to qom-get by using cached value when offset > 0
> + if offset == 0 or not self.prop_cache.has_key(path):
> + directory, prop = path.rsplit('/', 1)
> + try:
> + resp = str(self.qmp.command('qom-get', path=directory,
> property=prop))
> + self.prop_cache[path] = resp + '\n' # make values shell
> friendly
> + except:
> + return -EPERM
> +
> + data = self.prop_cache[path]
>
> if offset > len(data):
> return ''
> @@ -111,13 +116,18 @@ class QOMFS(Fuse):
> 0,
> 0))
> elif self.is_property(path):
> + directory, prop = path.rsplit('/', 1)
> + try:
> + resp = str(self.qmp.command('qom-get', path=directory,
> property=prop))
> + except:
> + return -ENOENT
> value = posix.stat_result((0644 | stat.S_IFREG,
> self.get_ino(path),
> 0,
> 1,
> 1000,
> 1000,
> - 4096,
> + max(len(resp) * 2, 4096),
> 0,
> 0,
> 0))
> --
> 1.7.9.5
