Richard W.M. Jones
2022-Jan-31 13:10 UTC
[Libguestfs] [PATCH nbdkit] plugins: python: Add error example
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 at 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 at 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
Nir Soffer
2022-Jan-31 13:17 UTC
[Libguestfs] [PATCH nbdkit] plugins: python: Add error example
On Mon, Jan 31, 2022 at 3:10 PM Richard W.M. Jones <rjones at 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 at 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> > Reviewed-by: Richard W.M. Jones <rjones at 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 >