[Libguestfs] [PATCH nbdkit 3/3] tests: Test export flags (eflags).

[Eric Blake]

On 12/14/18 4:16 PM, Richard W.M. Jones wrote:
> ---
>   tests/Makefile.am    |   3 +
>   tests/test-eflags.sh | 222 +++++++++++++++++++++++++++++++++++++++++++
>   2 files changed, 225 insertions(+)
> 

> +# Test export flags.
> +#
> +# Run nbdkit with various can_* callbacks defined and with or without
> +# the -r flag, and check that nbdkit constructs the export flags
> +# controlling READ_ONLY, ROTATIONAL, SEND_TRIM, etc. as expected.
> +#
> +# We use the oldstyle (-o) protocol here because it's simpler to read
> +# out the eflags.

Indeed - the client has to talk in newstyle, but not in oldstyle :)

>    We use the shell plugin because it gives maximum
> +# control over the can_* callbacks (at least, max without having to
> +# write a C plugin).
> +
> +source ./functions.sh
> +set -e
> +
> +if ! socat -h >/dev/null; then
> +    echo "$0: 'socat' command not available"
> +    exit 77
> +fi
> +
> +# Check 'od' command exists and can do endian swaps (which the FreeBSD
> +# version cannot).

Do we need endian swaps, or can we just read one byte at a time and then 
reconstruct things by hand (after all, we know the bytes are in network 
order, so we don't have to worry about whether we are running on a big- 
or little-endian machine to do the integer math to build up the 16-bit 
value from those two bytes).

> +if ! od --endian=big </dev/null >/dev/null; then
> +    echo "$0: 'od' command not available or doesn't support endian swaps"
> +    exit 77
> +fi
> +
> +files="eflags.out"
> +rm -f $files
> +cleanup_fn rm -f $files
> +
> +# The export flags.
> +# See also src/protocol.h

Comment may need tweaking if I finish my patches to move src/proto* to 
common/proto/.  We'll see what lands first :)

> +HAS_FLAGS=$((         1 << 0 ))
> +READ_ONLY=$((         1 << 1 ))
> +SEND_FLUSH=$((        1 << 2 ))
> +SEND_FUA=$((          1 << 3 ))
> +ROTATIONAL=$((        1 << 4 ))
> +SEND_TRIM=$((         1 << 5 ))
> +SEND_WRITE_ZEROES=$(( 1 << 6 ))
> +
> +all_flags="HAS_FLAGS READ_ONLY SEND_FLUSH SEND_FUA ROTATIONAL SEND_TRIM SEND_WRITE_ZEROES"

Well, that's all the flags we currently drive, although more flags exist 
(and we may eventually patch nbdkit to drive those, as well).

> +
> +do_nbdkit ()
> +{
> +    nbdkit -v -U - -o "$@" sh script=- --run '
> +        socat -b 28 unix-connect:$unixsocket \
> +            exec:"dd bs=1 skip=26 count=2 of=eflags.out status=none"

dd can portably do byteswaps, with conv=swab, but then you have to know 
if you are big- or little-endian to know whether to use it.

> +    '
> +
> +    # By adding 0 we convert the string to an integer (removing
> +    # whitespace).
> +    eflags=$((0 + $(od --endian=big -An -N2 -d < eflags.out)))

So back to my earlier thought of just reading 1 byte at a time and 
building up the value ourselves:

eflags=$(( ($(od -An -N1     -tu1 eflags.out) << 8) |
             $(od -An -N1 -j1 -tu1 eflags.out)         ))

> +    printf "eflags 0x%04x" $eflags
> +    for f in $all_flags; do
> +        [ $(( eflags & ${!f} )) -ne 0 ] && echo -n " $f"
> +    done
> +    echo
> +}
> +

> +
> +# no -r
> +# can_write=true
> +#
> +# NBD_FLAG_SEND_WRITE_ZEROES is always set on writable connections
> +# even if can_zero returns false, because nbdkit reckons it can
> +# emulate zeroing using pwrite.

And we have the nozero filter if we want things otherwise (if you want 
to use that in this test).

Otherwise, this looks sane.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org