[Libguestfs] [PATCH libnbd 4/9] golang: aio_buffer.go: Add MakeAioBufferZero()

[Eric Blake]

On Sun, Jan 30, 2022 at 01:33:32AM +0200, Nir Soffer wrote:
> Make it easy to create a zeroed buffer via calloc(), preventing leaking
> sensitive info from the heap.
> 
> Benchmarking show that creating a zeroed buffer is much slower compared

shows

> with uninitialized buffer, but much faster compared with manually
> initializing the buffer with a loop.
> 
> BenchmarkMakeAioBuffer-12        	 7252674	       148.1 ns/op
> BenchmarkMakeAioBufferZero-12    	  262107	      4181 ns/op
> BenchmarkAioBufferZero-12        	   17581	     68759 ns/op
> 
> It is interesting that creating a zeroed buffer is 3 times faster
> compared with making a new []byte slice:
> 
> BenchmarkMakeAioBufferZero-12    	  247710	      4440 ns/op
> BenchmarkMakeByteSlice-12        	   84117	     13733 ns/op

Some of this is due to how much vectorization the standard library
(whether libc or Go's core libraries) can do when bulk-zeroing
(zeroing 64 bits, or even a cache line at a time, in an unrolled loop,
is always going to be more performant than a naive loop of one byte at
a time).

> 
> Signed-off-by: Nir Soffer <nsoffer at redhat.com>
> ---
>  golang/aio_buffer.go                 |  6 ++++++
>  golang/libnbd_620_aio_buffer_test.go | 16 ++++++++++++++++

Another file that may fit better in the 0xx naming, especially if we
decide to duplicate similar functionality into the python or OCaml
bindings of being able to pre-generate a known-zero buffer for use in
passing to nbd_pread.

As a helper API, this seems useful.  But do we need any man page
documentation of a language-specific helper function?

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
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