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

On Fri, Dec 14, 2018 at 04:31:32PM -0600, Eric Blake wrote: > 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? Actually I tried using just "-" (for the first time, I didn't try it before) and it works. So the above can be written: nbdkit sh - <<'EOF' case "$1" in get_size) echo 1M ;; pread) dd if=/dev/zero count=$3 iflag=count_bytes ;; *) exit 2 ;; esac EOF At least on Linux. I wonder if that also works on FreeBSD etc and if it depends on an implementation detail of the parser. I'll have to do some more investigations.

Rich. > 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 -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones Read my programming and virtualization blog: http://rwmj.wordpress.com virt-top is 'top' for virtual machines. Tiny program with many powerful monitoring features, net stats, disk stats, logging, etc. http://people.redhat.com/~rjones/virt-top