Message ID | 1343150454-4677-13-git-send-email-mdroth@linux.vnet.ibm.com |
---|---|
State | New |
Headers | show |
Michael Roth <mdroth@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 <aliguori@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 <mdroth@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
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))
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 <mdroth@linux.vnet.ibm.com> --- QMP/qom-fuse | 24 +++++++++++++++++------- 1 file changed, 17 insertions(+), 7 deletions(-)