Re: [Libguestfs] [PATCH nbdkit] plugins: python: Add error example

On Mon, Jan 31, 2022 at 12:14 AM Nir Soffer <nsoffer(a)redhat.com&gt; wrote: > > This plugin simulates errors in pread, pwrite, and extents. This is > useful for testing error handling in NBD clients, and understanding how > plugin exceptions are reported to the NBD client. > --- > plugins/python/Makefile.am | 1 + > plugins/python/examples/error.py | 77 ++++++++++++++++++++++++++++++++ > 2 files changed, 78 insertions(+) > create mode 100644 plugins/python/examples/error.py > > diff --git a/plugins/python/Makefile.am b/plugins/python/Makefile.am > index eecd7e89..e6e6c9e6 100644 > --- a/plugins/python/Makefile.am > +++ b/plugins/python/Makefile.am > @@ -27,20 +27,21 @@ > # ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, > # OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT > # OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF > # SUCH DAMAGE. > > include $(top_srcdir)/common-rules.mk > > EXTRA_DIST = \ > nbdkit-python-plugin.pod \ > examples/file.py \ > + examples/error.py \ > examples/imageio.py \ > examples/ramdisk.py \ > examples/url.py \ > $(NULL) > > if HAVE_PYTHON > > plugin_LTLIBRARIES = nbdkit-python-plugin.la > > nbdkit_python_plugin_la_SOURCES = \ > diff --git a/plugins/python/examples/error.py b/plugins/python/examples/error.py > new file mode 100644 > index 00000000..0331a83e > --- /dev/null > +++ b/plugins/python/examples/error.py > @@ -0,0 +1,77 @@ > +# Example Python plugin. > +# > +# This plugin simulates errors for testing NBD client error hanlding. > +# Every odd call will fail, and every even call will succeed, unless > +# there a real error accesing the specified file. > +# > +# This example can be freely used for any purpose. > + > +# Run it from the build directory like this: > +# > +# ./nbdkit -f -v python ./plugins/python/examples/error.py file=test.img > +# > +# Or run it after installing nbdkit like this: > +# > +# nbdkit -f -v python ./plugins/python/examples/error.py file=test.img > +# > +# The -f -v arguments are optional. They cause the server to stay in > +# the foreground and print debugging, which is useful when testing. > + > +import os > + > +API_VERSION = 2 > + > +filename = None > +calls = 0 > + > + > +def config(key, value): > + global filename > + assert key == "file" > + filename = value > + > + > +def open(readonly): > + flags = os.O_RDONLY if readonly else os.O_RDWR > + return {"fd": os.open(filename, flags)} > + > + > +def can_extents(h): > + return True > + > + > +def get_size(h): > + return os.stat(h["fd"]).st_size > + > + > +def extents(h, count, offset, flags): > + global calls > + calls += 1 > + if calls % 2: > + raise RuntimeError(f"extents error offset={offset} count={count}") > + > + # We don't really support extents, so we report the entire file as > + # data. > + return [(offset, count, 0)] > + > + > +def pread(h, buf, offset, flags): > + global calls > + calls += 1 > + if calls % 2: > + raise RuntimeError(f"pread error offset={offset} count={len(buf)}") > + > + os.lseek(h["fd"], offset, os.SEEK_SET) > + n = os.readv(h['fd'], [buf]) We can use os.preadv in current python, but I'm trying to keep this plugin useful on rhel 8 systems (python 3.6). os.preadv added in python 3.7.

> + assert n == len(buf) > + > + > +def pwrite(h, buf, offset, flags): > + global calls > + calls += 1 > + if calls % 2: > + raise RuntimeError(f"pwrite error offset={offset} count={len(buf)}") > + > + os.lseek(h["fd"], offset, os.SEEK_SET) > + n = os.writev(h['fd'], [buf]) > + assert n == len(buf) > -- > 2.34.1 >