7:33 a.m.
On Mon, Jan 31, 2022 at 03:17:21PM +0200, Nir Soffer wrote:
On Mon, Jan 31, 2022 at 3:10 PM Richard W.M. Jones
<rjones(a)redhat.com> wrote:
>
> On Mon, Jan 31, 2022 at 12:17:36AM +0200, Nir Soffer wrote:
> > On Mon, Jan 31, 2022 at 12:14 AM Nir Soffer <nsoffer(a)redhat.com> 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.
>
> The default thread model for Python plugins is
> nbdkit.THREAD_MODEL_SERIALIZE_ALL_REQUESTS, ie. you cannot have two
> pread() functions racing to do lseek + readon the same file
> descriptor, so this should be safe.
Should I make this explicit?
def thread_model():
# Serialize requests so we can seek safely in pread and pwrite.
return nbdkit.THREAD_MODEL_SERIALIZE_ALL_REQUESTS
Yup, could be worth making that clear since it's an example.
Rich.
>
> Reviewed-by: Richard W.M. Jones <rjones(a)redhat.com>
>
> Rich.
>
> > > + 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
> > >
>
> --
> Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
> Read my programming and virtualization blog: http://rwmj.wordpress.com
> libguestfs lets you edit virtual machines. Supports shell scripting,
> bindings from many languages. http://libguestfs.org
>
--
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
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