In some situations getting image extents can be slow. Add configuration value to simulate slow extents. This can be useful for testing and optimizing nbd clients. Example usage - simulating 1 seconds delay: qemu-img create -f raw test.img 10g ./nbdkit -f -v python ./plugins/python/examples/file.py \ file=test.img extents_delay=1 2>&1 | grep 'python: extents' nbdkit: python.1: debug: python: extents count=2147483136 offset=0 req_one=1 nbdkit: python.0: debug: python: extents count=2147483136 offset=2147483136 req_one=1 nbdkit: python.2: debug: python: extents count=2147483136 offset=4294966272 req_one=1 nbdkit: python.3: debug: python: extents count=2147483136 offset=6442449408 req_one=1 nbdkit: python.5: debug: python: extents count=2147483136 offset=8589932544 req_one=1 nbdkit: python.6: debug: python: extents count=2560 offset=10737415680 req_one=1 nbdkit: python.4: debug: python: extents count=2147483136 offset=0 req_one=1 nbdkit: python.9: debug: python: extents count=2147483136 offset=2147483136 req_one=1 nbdkit: python.14: debug: python: extents count=2147483136 offset=4294966272 req_one=1 nbdkit: python.11: debug: python: extents count=2147483136 offset=6442449408 req_one=1 nbdkit: python.9: debug: python: extents count=2147483136 offset=8589932544 req_one=1 nbdkit: python.9: debug: python: extents count=2560 offset=10737415680 req_one=1 In another shell: $ time qemu-img convert -p -f raw -O raw nbd://localhost/ test.img (100.00/100%) real 0m18.029s user 0m2.314s sys 0m3.581s Without extent delay this takes about 5.6 seconds. Signed-off-by: Nir Soffer <nsoffer(a)redhat.com&gt; --- plugins/python/examples/file.py | 22 +++++++++++++++++++++- 1 file changed, 21 insertions(+), 1 deletion(-) diff --git a/plugins/python/examples/file.py b/plugins/python/examples/file.py index 8501b8eb..e607b338 100644 --- a/plugins/python/examples/file.py +++ b/plugins/python/examples/file.py @@ -6,6 +6,11 @@ # # ./nbdkit -f -v python ./plugins/python/examples/file.py file=test.img # +# To simulate slow extents operation, specify a delay: +# +# ./nbdkit -f -v python ./plugins/python/examples/file.py file=test.img \ +# extents_delay=70 +# # Or run it after installing nbdkit like this: # # nbdkit -f -v python ./plugins/python/examples/file.py file=test.img @@ -14,6 +19,7 @@ # the foreground and print debugging, which is useful when testing. import os +import time import nbdkit @@ -25,13 +31,18 @@ API_VERSION = 2 # The file we want to serve. filename = None +# Simulate slow extents. +extents_delay = 0.0 + # Parse the file parameter which contains the name of the file that we # want to serve. def config(key, value): - global filename + global filename, extents_delay if key == "file": filename = os.path.abspath(value) + elif key == "extents_delay": + extents_delay = float(value) else: raise RuntimeError("unknown parameter: " + key) @@ -64,6 +75,15 @@ def get_size(h): return sb.st_size +def can_extents(h): + return True + + +def extents(h, count, offset, flags): + time.sleep(extents_delay) + yield (offset, count, 0) + + def pread(h, buf, offset, flags): n = os.preadv(h['fd'], [buf], offset) if n != len(buf): -- 2.26.2