[Libguestfs] [PATCH nbdkit 1/3] sh: Implement inline scripts.
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.
---
plugins/sh/nbdkit-sh-plugin.pod | 17 ++++++++++
plugins/sh/sh.c | 55 ++++++++++++++++++++++++++++++++-
2 files changed, 71 insertions(+), 1 deletion(-)
diff --git a/plugins/sh/nbdkit-sh-plugin.pod b/plugins/sh/nbdkit-sh-plugin.pod
index 371de5f..0644c36 100644
--- a/plugins/sh/nbdkit-sh-plugin.pod
+++ b/plugins/sh/nbdkit-sh-plugin.pod
@@ -6,6 +6,10 @@ nbdkit-sh-plugin - nbdkit shell, script or executable plugin
nbdkit sh /path/to/script [arguments...]
+ nbdkit sh script=- [arguments...] <<'EOF'
+ ... shell script here ...
+ EOF
+
=head1 DESCRIPTION
C<nbdkit-sh-plugin> allows you to write plugins for L<nbdkit(1)> using
@@ -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
+
=head1 WRITING AN NBDKIT SH PLUGIN
For an example plugin written in Bash, see:
diff --git a/plugins/sh/sh.c b/plugins/sh/sh.c
index 368f1eb..fcd839b 100644
--- a/plugins/sh/sh.c
+++ b/plugins/sh/sh.c
@@ -39,6 +39,7 @@
#include <string.h>
#include <unistd.h>
#include <errno.h>
+#include <sys/stat.h>
#include <nbdkit-plugin.h>
@@ -115,6 +116,50 @@ sh_dump_plugin (void)
}
}
+/* This implements the "inline script" feature (script=-). Read stdin
+ * into a temporary file and return the name of the file which the
+ * caller must free. For convenience we put the temporary file into
+ * tmpdir but that's an implementation detail.
+ */
+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) {
+ nbdkit_error ("asprintf: %m");
+ goto err;
+ }
+
+ if (system (cmd) != 0) {
+ nbdkit_error ("sh: failed to copy inline script to temporary file");
+ goto err;
+ }
+
+ if (chmod (filename, 0500) == -1) {
+ nbdkit_error ("chmod: %s: %m", filename);
+ goto err;
+ }
+
+ free (cmd);
+ return filename;
+
+ err:
+ free (filename);
+ free (cmd);
+ return NULL;
+}
+
static int
sh_config (const char *key, const char *value)
{
@@ -124,7 +169,15 @@ sh_config (const char *key, const char *value)
nbdkit_error ("the first parameter must be script=/path/to/script");
return -1;
}
- script = nbdkit_realpath (value);
+
+ /* If the script name is not "-" then it's expected to be a
+ * filename, otherwise it's an inline script which must be read
+ * into a temporary file. Either way we want an absolute path.
+ */
+ if (strcmp (value, "-") != 0)
+ script = nbdkit_realpath (value);
+ else
+ script = inline_script ();
if (script == NULL)
return -1;
--
2.19.2