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.
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
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