[Libguestfs] [PATCH nbdkit 6/7] cache: Add cache-min-block-size parameter

[Richard W.M. Jones]

On Wed, Aug 04, 2021 at 10:47:34AM +0200, Martin Kletzander wrote:
> >+# Run nbdkit with the caching filter.
> >+start_nbdkit -P cache-block-size.pid -U $sock --filter=cache \
> >+             file cache-block-size.img cache-min-block-size=64K
> >+
> >+nbdsh --connect "nbd+unix://?socket=$sock" \
> >+      -c '
> >+# Write some pattern data to the overlay and check it reads back OK.
> >+buf = b"abcd" * 16384
> >+h.pwrite(buf, 32768)
> >+zero = h.pread(32768, 0)
> >+assert zero == bytearray(32768)
> >+buf2 = h.pread(65536, 32768)
> >+assert buf == buf2
> >+
> >+# Flushing should write through to the underlying file.
> >+h.flush()
> >+
> >+with open("cache-block-size.img", "rb") as file:
> >+    zero = file.read(32768)
> >+    assert zero == bytearray(32768)
> >+    buf2 = file.read(65536)
> >+    assert buf == buf2
> >+'
> 
> 
> I do not see how this checks that the min block size is respected.  I
> would expect something along the lines of:
> 
> 1) read 32k
> 2) write to the underlying file past those 32k
> 3) read another 32k (from offset == 32k)
> 4) check that the last read returned original data and not those written
>    in step 2)

Yes this test is not great.  I think it was basically copied from this
one:

https://gitlab.com/nbdkit/nbdkit/-/blob/master/tests/test-cache.sh

I'll see if I can rethink this once I've got the v2v stuff out of the
way unless someone else comes up with a fix.

Rich.

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