From patchwork Fri Oct 12 21:11:00 2012 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Subject: [v4,18/26] qom-fuse: workaround for truncated properties > 4096 Date: Fri, 12 Oct 2012 11:11:00 -0000 From: Michael Roth X-Patchwork-Id: 191242 Message-Id: <1350076268-18461-19-git-send-email-mdroth@linux.vnet.ibm.com> To: qemu-devel@nongnu.org Cc: kwolf@redhat.com, peter.maydell@linaro.org, aliguori@us.ibm.com, blauwirbel@gmail.com, pbonzini@redhat.com 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. Reviewed-by: Anthony Liguori Reviewed-by: Paolo Bonzini Signed-off-by: Michael Roth --- QMP/qom-fuse | 24 +++++++++++++++++------- 1 file changed, 17 insertions(+), 7 deletions(-) diff --git a/QMP/qom-fuse b/QMP/qom-fuse index b4a4eb3..bbad0de 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))