Re: [PATCH v6 5/6] unpack-objects.c: add dry_run mode for get_data()

> From: Han Xin <hanxin.hx@alibaba-inc.com>
>
> In dry_run mode, "get_data()" is used to verify the inflation of data,
> and the returned buffer will not be used at all and will be freed
> immediately. Even in dry_run mode, it is dangerous to allocate a
> full-size buffer for a large blob object. Therefore, only allocate a
> low memory footprint when calling "get_data()" in dry_run mode.

>
> Suggested-by: Jiang Xin <zhiyou.jx@alibaba-inc.com>
> Signed-off-by: Han Xin <hanxin.hx@alibaba-inc.com>
> ---
>  builtin/unpack-objects.c | 23 +++++++++++++++++------
>  1 file changed, 17 insertions(+), 6 deletions(-)
>
> diff --git a/builtin/unpack-objects.c b/builtin/unpack-objects.c
> index 4a9466295b..c4a17bdb44 100644
> --- a/builtin/unpack-objects.c
> +++ b/builtin/unpack-objects.c
> @@ -96,15 +96,21 @@ static void use(int bytes)
>  	display_throughput(progress, consumed_bytes);
>  }
>
> -static void *get_data(unsigned long size)
> +static void *get_data(unsigned long size, int dry_run)
>  {
>  	git_zstream stream;
> -	void *buf = xmallocz(size);
> +	unsigned long bufsize;
> +	void *buf;
>
>  	memset(&stream, 0, sizeof(stream));
> +	if (dry_run && size > 8192)
> +		bufsize = 8192;
> +	else
> +		bufsize = size;
> +	buf = xmallocz(bufsize);
>
>  	stream.next_out = buf;
> -	stream.avail_out = size;
> +	stream.avail_out = bufsize;
>  	stream.next_in = fill(1);
>  	stream.avail_in = len;
>  	git_inflate_init(&stream);
> @@ -124,6 +130,11 @@ static void *get_data(unsigned long size)
>  		}
>  		stream.next_in = fill(1);
>  		stream.avail_in = len;
> +		if (dry_run) {
> +			/* reuse the buffer in dry_run mode */
> +			stream.next_out = buf;
> +			stream.avail_out = bufsize;
> +		}
>  	}
>  	git_inflate_end(&stream);
>  	return buf;
> @@ -323,7 +334,7 @@ static void added_object(unsigned nr, enum object_type type,
>  static void unpack_non_delta_entry(enum object_type type, unsigned long size,
>  				   unsigned nr)
>  {
> -	void *buf = get_data(size);
> +	void *buf = get_data(size, dry_run);
>
>  	if (!dry_run && buf)
>  		write_object(nr, type, buf, size);
> @@ -357,7 +368,7 @@ static void unpack_delta_entry(enum object_type type, unsigned long delta_size,
>  	if (type == OBJ_REF_DELTA) {
>  		oidread(&base_oid, fill(the_hash_algo->rawsz));
>  		use(the_hash_algo->rawsz);
> -		delta_data = get_data(delta_size);
> +		delta_data = get_data(delta_size, dry_run);
>  		if (dry_run || !delta_data) {
>  			free(delta_data);
>  			return;
> @@ -396,7 +407,7 @@ static void unpack_delta_entry(enum object_type type, unsigned long delta_size,
>  		if (base_offset <= 0 || base_offset >= obj_list[nr].offset)
>  			die("offset value out of bound for delta base object");
>
> -		delta_data = get_data(delta_size);
> +		delta_data = get_data(delta_size, dry_run);
>  		if (dry_run || !delta_data) {
>  			free(delta_data);
>  			return;