[Libguestfs] [PATCH nbdkit 1/3] sh: Implement inline scripts.

[Eric Blake]

On 12/14/18 4:16 PM, Richard W.M. Jones wrote:
> This implements something like a readonly 1MB disk reading as zeroes:
> 
> nbdkit sh script=- <<'EOF'
>    case "$1" in
>      get_size) echo 1M ;;
>      pread) dd if=/dev/zero count=$3 iflag=count_bytes ;;
>      *) exit 2 ;;
>    esac
> EOF
> 
> Use of "-" is analogous to reading passwords from stdin.
> ---

> @@ -26,6 +30,19 @@ like this:
>   You may have to add further C<key=value> arguments to the command
>   line.
>   
> +=head2 Inline shell scripts
> +
> +It is also possible to write a shell script plugin "inline" using C<->
> +as the name of the script, like this:
> +
> + nbdkit sh script=- <<'EOF'
> +   case "$1" in
> +     get_size) echo 1M ;;
> +     pread) dd if=/dev/zero count=$3 iflag=count_bytes ;;
> +     *) exit 2 ;;
> +   esac
> + EOF
> +

Worth a specific mention that 'script=' is required, since otherwise the 
'-' looks like an option to nbdkit proper rather than a script parameter?

Probably not worth a mention that a local file named '-' can still be 
invoked via [script=]./- (there, script is optional because the leading 
./ avoids the leading -).

> +static char *
> +inline_script (void)
> +{
> +  const char scriptname[] = "inline-script.sh";
> +  char *filename = NULL;
> +  char *cmd = NULL;
> +
> +  if (asprintf (&filename, "%s/%s", tmpdir, scriptname) == -1) {
> +    nbdkit_error ("asprintf: %m");
> +    goto err;
> +  }
> +
> +  /* Safe because both the tmpdir and script name are controlled by us
> +   * and don't contain characters that need quoting.
> +   */
> +  if (asprintf (&cmd, "cat > %s", filename) == -1) {

Useful comment :) And I verified it is true.

Looks good.

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