[Libguestfs] [RFC nbdkit PATCH 4/4] sh, eval: Add .list_exports support
Eric Blake
eblake at redhat.com
Fri Jul 31 22:22:32 UTC 2020
Exposing .list_exports through to shell scripts makes testing export
listing a lot more feasible. The design chosen here is amenable to
'ls -1' or 'find' output provided there are no newlines or whitespace
in the files being listed (the user gives up descriptions in that
case), while also being flexible enough to support names or
descriptions with arbitrary content. One idea that might be worth
considering for future patches is parsing a magic header line
describing how the rest of the input would be parsed, where the first
line being unrecognized uses a default format, but other magic words
can introduce alternative formats that might be easier to produce
within scripts.
Signed-off-by: Eric Blake <eblake at redhat.com>
---
RFC because the test is incomplete (in part because of libnbd
bugs that I discovered which need fixing first).
plugins/eval/nbdkit-eval-plugin.pod | 2 +
plugins/sh/nbdkit-sh-plugin.pod | 31 ++++++++++
tests/Makefile.am | 2 +
plugins/sh/methods.h | 4 +-
plugins/eval/eval.c | 2 +
plugins/sh/methods.c | 91 +++++++++++++++++++++++++++++
plugins/sh/sh.c | 1 +
plugins/sh/example.sh | 8 +++
tests/test-eval-exports.sh | 65 +++++++++++++++++++++
9 files changed, 205 insertions(+), 1 deletion(-)
create mode 100755 tests/test-eval-exports.sh
diff --git a/plugins/eval/nbdkit-eval-plugin.pod b/plugins/eval/nbdkit-eval-plugin.pod
index 7e25a01f..7126c6de 100644
--- a/plugins/eval/nbdkit-eval-plugin.pod
+++ b/plugins/eval/nbdkit-eval-plugin.pod
@@ -108,6 +108,8 @@ features):
=item B<is_rotational=>SCRIPT
+=item B<list_exports=>SCRIPT
+
=item B<open=>SCRIPT
=item B<pread=>SCRIPT
diff --git a/plugins/sh/nbdkit-sh-plugin.pod b/plugins/sh/nbdkit-sh-plugin.pod
index 771c6bc0..303e96a7 100644
--- a/plugins/sh/nbdkit-sh-plugin.pod
+++ b/plugins/sh/nbdkit-sh-plugin.pod
@@ -266,6 +266,37 @@ with status C<1>; unrecognized output is ignored.
/path/to/script preconnect <readonly> <exportname>
+=item C<list_exports>
+
+ /path/to/script list_exports <readonly> <default_only>
+
+The C<readonly> parameter will be C<true> or C<false>. The
+C<default_only> parameter will be C<true> if the caller is only
+interested in the canonical name of the default export, or C<false> to
+get a full list of export names; the script may safely ignore this
+parameter and always provide a full list if desired.
+
+This must print, one per line on stdout, a list of zero or more export
+declarations in the format:
+
+ name [description...]
+
+which correspond to the inputs of the C C<nbdkit_add_export> function
+(see L<nbdkit-plugin(3)>). Within the line, the sequence C<\n> is an
+escape for a literal newline, and all other uses of backslash escape
+the next character. The C<name> field is mandatory; if it begins with
+a single quote C<'>, it ends on the first matching unescaped single
+quote (with the quotes not part of the name), otherwise the name ends
+at the first unescaped whitespace. Any text remaining on the line
+after C<name> is treated as the C<description>, with unescaped leading
+and trailing whitespace stripped. Note that if none of the files in a
+directory contain backslash, single quote, or whitespace in their
+names, then the output of C<ls> will list names without descriptions.
+
+This method is I<not> required; if it is absent, the list of exports
+advertised by nbdkit will be the single export with the empty string
+as a name and no description.
+
=item C<open>
/path/to/script open <readonly> <exportname>
diff --git a/tests/Makefile.am b/tests/Makefile.am
index 129e0647..e3c42219 100644
--- a/tests/Makefile.am
+++ b/tests/Makefile.am
@@ -614,10 +614,12 @@ test_data_LDADD = libtest.la $(LIBGUESTFS_LIBS)
TESTS += \
test-eval.sh \
test-eval-file.sh \
+ test-eval-exports.sh \
$(NULL)
EXTRA_DIST += \
test-eval.sh \
test-eval-file.sh \
+ test-eval-exports.sh \
$(NULL)
# file plugin test.
diff --git a/plugins/sh/methods.h b/plugins/sh/methods.h
index 08a5ed17..69017fa4 100644
--- a/plugins/sh/methods.h
+++ b/plugins/sh/methods.h
@@ -1,5 +1,5 @@
/* nbdkit
- * Copyright (C) 2018 Red Hat Inc.
+ * Copyright (C) 2018-2020 Red Hat Inc.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are
@@ -44,6 +44,8 @@ extern int sh_thread_model (void);
extern int sh_get_ready (void);
extern int sh_after_fork (void);
extern int sh_preconnect (int readonly);
+extern int sh_list_exports (int readonly, int default_only,
+ struct nbdkit_exports *exports);
extern void *sh_open (int readonly);
extern void sh_close (void *handle);
extern int64_t sh_get_size (void *handle);
diff --git a/plugins/eval/eval.c b/plugins/eval/eval.c
index 54c5029e..2bd5e79f 100644
--- a/plugins/eval/eval.c
+++ b/plugins/eval/eval.c
@@ -74,6 +74,7 @@ static const char *known_methods[] = {
"get_ready",
"get_size",
"is_rotational",
+ "list_exports",
"missing",
"open",
"pread",
@@ -393,6 +394,7 @@ static struct nbdkit_plugin plugin = {
.after_fork = sh_after_fork,
.preconnect = sh_preconnect,
+ .list_exports = sh_list_exports,
.open = sh_open,
.close = sh_close,
diff --git a/plugins/sh/methods.c b/plugins/sh/methods.c
index 8257103e..a4422238 100644
--- a/plugins/sh/methods.c
+++ b/plugins/sh/methods.c
@@ -225,6 +225,97 @@ struct sh_handle {
int can_zero;
};
+static int
+parse_exports (const char *script,
+ const char *s, size_t slen, struct nbdkit_exports *exports)
+{
+ FILE *fp = NULL;
+ CLEANUP_FREE char *line = NULL;
+ size_t linelen = 0;
+ ssize_t len;
+ int ret = -1;
+
+ fp = fmemopen ((void *) s, slen, "r");
+ if (!fp) {
+ nbdkit_error ("%s: fmemopen: %m", script);
+ goto out;
+ }
+
+ while ((len = getline (&line, &linelen, fp)) != -1) {
+ bool quoted = *line == '\'';
+ char *p = line, *q = p + quoted, *desc;
+
+ /* Modify line in-place with our parse of name */
+ while (q - line < len && (quoted ? *q != '\'' : !ascii_isspace (*q))) {
+ if (*q == '\\') {
+ q++;
+ if (*q == 'n')
+ *q = '\n';
+ }
+ *p++ = *q++;
+ }
+ /* Transition from name to description */
+ *p++ = '\0';
+ q++;
+ while (ascii_isspace (*q))
+ q++;
+ p = desc = q;
+ while (q - line < len) {
+ if (*q == '\\') {
+ q++;
+ if (*q == 'n')
+ *q = '\n';
+ }
+ *p++ = *q++;
+ }
+ while (p > desc && ascii_isspace (p[-1]))
+ p--;
+ *p = '\0';
+
+ nbdkit_debug ("%s: adding export '%s' '%s'", script, line, desc);
+ if (nbdkit_add_export (exports, line, desc) == -1)
+ goto out;
+ }
+
+ ret = 0;
+
+ out:
+ if (fp)
+ fclose (fp);
+ return ret;
+}
+
+int
+sh_list_exports (int readonly, int default_only,
+ struct nbdkit_exports *exports)
+{
+ const char *method = "list_exports";
+ const char *script = get_script (method);
+ const char *args[] = { script, method, readonly ? "true" : "false",
+ default_only ? "true" : "false", NULL };
+ CLEANUP_FREE char *s = NULL;
+ size_t slen;
+
+ switch (call_read (&s, &slen, args)) {
+ case OK:
+ return parse_exports (script, s, slen, exports);
+
+ case MISSING:
+ return nbdkit_add_export (exports, "", NULL);
+
+ case ERROR:
+ return -1;
+
+ case RET_FALSE:
+ nbdkit_error ("%s: %s method returned unexpected code (3/false)",
+ script, method);
+ errno = EIO;
+ return -1;
+
+ default: abort ();
+ }
+}
+
void *
sh_open (int readonly)
{
diff --git a/plugins/sh/sh.c b/plugins/sh/sh.c
index 9e484823..374888a4 100644
--- a/plugins/sh/sh.c
+++ b/plugins/sh/sh.c
@@ -300,6 +300,7 @@ static struct nbdkit_plugin plugin = {
.after_fork = sh_after_fork,
.preconnect = sh_preconnect,
+ .list_exports = sh_list_exports,
.open = sh_open,
.close = sh_close,
diff --git a/plugins/sh/example.sh b/plugins/sh/example.sh
index 99e4e890..a6550055 100755
--- a/plugins/sh/example.sh
+++ b/plugins/sh/example.sh
@@ -85,6 +85,14 @@ case "$1" in
echo parallel
;;
+ list_exports)
+ # The following lists the names of all files in the current
+ # directory that do not contain whitespace, backslash, or single
+ # quotes. No description accompanies the export names.
+ # The first file listed is used when a client requests export ''.
+ find . -type f \! -name "*['\\\\[:space:]]*"
+ ;;
+
open)
# Open a new client connection.
diff --git a/tests/test-eval-exports.sh b/tests/test-eval-exports.sh
new file mode 100755
index 00000000..e9f99565
--- /dev/null
+++ b/tests/test-eval-exports.sh
@@ -0,0 +1,65 @@
+#!/usr/bin/env bash
+# nbdkit
+# Copyright (C) 2018-2020 Red Hat Inc.
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions are
+# met:
+#
+# * Redistributions of source code must retain the above copyright
+# notice, this list of conditions and the following disclaimer.
+#
+# * Redistributions in binary form must reproduce the above copyright
+# notice, this list of conditions and the following disclaimer in the
+# documentation and/or other materials provided with the distribution.
+#
+# * Neither the name of Red Hat nor the names of its contributors may be
+# used to endorse or promote products derived from this software without
+# specific prior written permission.
+#
+# THIS SOFTWARE IS PROVIDED BY RED HAT AND CONTRIBUTORS ''AS IS'' AND
+# ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
+# THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
+# PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL RED HAT OR
+# CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
+# USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
+# ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+# OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+# OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+# SUCH DAMAGE.
+
+# This is an example from the nbdkit-eval-plugin(1) manual page.
+# Check here that it doesn't regress.
+
+source ./functions.sh
+set -e
+set -x
+
+requires nbdsh -c 'print (h.get_list_export_description)'
+requires nbdinfo --help
+requires jq --version
+
+files="eval-exports.list eval-exports.out"
+rm -f $files
+cleanup_fn rm -f $files
+
+# Control case: no list_exports
+nbdkit -U - -v eval get_size='echo 0' \
+ --run 'nbdinfo --list --json "$uri"' > eval-exports.out
+cat eval-exports.out
+diff -u <(jq -c '[.exports[] | [."export-name", .description]]' \
+ eval-exports.out) - <<EOF
+[["",null]]
+EOF
+
+# Empty exports list produces 0 exports
+: >eval-exports.list
+nbdkit -U - -v eval list_exports='cat eval-exports.list' get_size='echo 0' \
+ --run 'nbdinfo --list --json "$uri"' > eval-exports.out
+cat eval-exports.out
+diff -u <(jq -c '[.exports[] | [."export-name", .description]]' \
+ eval-exports.out) - <<EOF
+[]
+EOF
--
2.28.0
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