[Libguestfs] [nbdkit PATCH] sh: Add exit status triggers for nbdkit_{shutdown, disconnect}
Laszlo Ersek
lersek at redhat.com
Wed Nov 2 13:15:45 UTC 2022
On 11/01/22 20:56, Eric Blake wrote:
> Make it possible for the sh and eval plugins to disconnect a client or
> shut down the entire nbdkit server by use of special return values.
> Prior to this patch we had reserved 4-7 for future use; this defines
> 4-6, and extends the set of reserved return values to 7-15. We figure
> it is unlikely that anyone is using status 8-15 with the intent that
> it behaves identically to status 1.
>
> For the testsuite, I only covered the eval plugin; but since it shares
> common code with the sh plugin, both styles should work.
> ---
>
> Finally got the testsuite additions for this in a state that I like.
>
> plugins/sh/nbdkit-sh-plugin.pod | 37 ++++++-
> tests/Makefile.am | 2 +
> plugins/sh/call.h | 9 +-
> plugins/sh/call.c | 85 +++++++--------
> tests/test-eval-disconnect.sh | 185 ++++++++++++++++++++++++++++++++
> 5 files changed, 268 insertions(+), 50 deletions(-)
> create mode 100755 tests/test-eval-disconnect.sh
>
> diff --git a/plugins/sh/nbdkit-sh-plugin.pod b/plugins/sh/nbdkit-sh-plugin.pod
> index 2a55fdc9..37139e1b 100644
> --- a/plugins/sh/nbdkit-sh-plugin.pod
> +++ b/plugins/sh/nbdkit-sh-plugin.pod
> @@ -96,4 +96,4 @@ The script should exit with specific exit codes:
>
> The method was executed successfully.
>
> -=item 1 and 8-127
> +=item 1 and 16-255
>
> There was an error. The script may print on stderr an errno name,
> optionally followed by whitespace and a message, for example:
> @@ -123,9 +123,38 @@ The requested method is not supported by the script.
>
> For methods which return booleans, this code indicates false.
>
> -=item 4, 5, 6, 7
> +=item S<4>
The S<> notation seems new here (so it's going to be inconsistent with
the rest of this file, I think).
>
> -These exit codes are reserved for future use.
> +Triggers a call to the C function C<nbdkit_shutdown>, which requests
> +an asynchronous exit of the nbdkit server (disconnecting all clients).
> +Since the client may get a response before shutdown is complete,
> +nbdkit then treats empty stderr as success for the current callback,
> +and parses non-empty stderr as if the script had exited with code
> +S<1>.
Exit codes 0 and 1 permit the following as well: the shell script may
output some preliminary diagnostics to stderr, but then exit with code
0. In that case, the command is considered successsful, and the script's
stderr is thrown away by nbdkit.
Should we parallel that here as well? That would require two separate
codes, like 4 and 5. They'd match error codes 0 and 1, except an async
shutdown would be initiated as well.
> +
> +=item S<5>
> +
> +Triggers a call to the C function C<nbdkit_disconnect> with C<force>
> +set to true, which requests an abrupt disconnect of the current
> +client. The contents of stderr are irrelevant with this status, since
> +the client will not get a response.
> +
> +=item S<6>
> +
> +Triggers a call to the C function C<nbdkit_disconnect> with C<force>
> +set to false, which requests a soft disconnect of the current client
> +(future client requests are rejected with C<ESHUTDOWN> without calling
> +into the plugin, but current requests may complete). Since the client
> +will likely get the response to this command, nbdkit then treats empty
> +stderr as success for the current callback, and parses non-empty
> +stderr as if the script had exited with code S<1>.
Same comment as for code 4.
I think allowing a script to output log messages but ultimately to
succeed is nice. (Including the case where "succeed" entails shutting
down the server.)
> +
> +=item 7-15
> +
> +These exit codes are reserved for future use. Note that versions of
> +nbdkit E<lt> 1.34 documented that codes S<8> through S<15> behaved
> +like code S<1>; although it is unlikely that many scripts relied on
> +this similarity in practice.
>
> =back
>
> @@ -578,4 +607,4 @@ Richard W.M. Jones
>
> =head1 COPYRIGHT
>
> -Copyright (C) 2018-2020 Red Hat Inc.
> +Copyright (C) 2018-2022 Red Hat Inc.
> diff --git a/tests/Makefile.am b/tests/Makefile.am
> index d59b797c..3994fc6a 100644
> --- a/tests/Makefile.am
> +++ b/tests/Makefile.am
> @@ -768,12 +768,14 @@ TESTS += \
> test-eval-file.sh \
> test-eval-exports.sh \
> test-eval-cache.sh \
> + test-eval-disconnect.sh \
> $(NULL)
> EXTRA_DIST += \
> test-eval.sh \
> test-eval-file.sh \
> test-eval-exports.sh \
> test-eval-cache.sh \
> + test-eval-disconnect.sh \
> $(NULL)
>
> # file plugin test.
> diff --git a/plugins/sh/call.h b/plugins/sh/call.h
> index 76de23a3..44767e81 100644
> --- a/plugins/sh/call.h
> +++ b/plugins/sh/call.h
> @@ -1,5 +1,5 @@
> /* nbdkit
> - * Copyright (C) 2018 Red Hat Inc.
> + * Copyright (C) 2018-2022 Red Hat Inc.
> *
> * Redistribution and use in source and binary forms, with or without
> * modification, are permitted provided that the following conditions are
> @@ -51,7 +51,12 @@ typedef enum exit_code {
> OK = 0,
> ERROR = 1, /* all script error codes are mapped to this */
> MISSING = 2, /* method missing */
> - RET_FALSE = 3 /* script exited with code 3 meaning false */
> + RET_FALSE = 3, /* script exited with code 3 meaning false */
> + SHUTDOWN = 4, /* call nbdkit_shutdown() before parsing stderr */
> + DISC_FORCE = 5, /* call nbdkit_disconnect(true) */
> + DISC_SOFT = 6, /* call nbdkit_disconnect(false) */
> + /* 7 is reserved since 1.8; handle like ERROR for now */
> + /* 8-15 are reserved since 1.34; handle like ERROR for now */
> } exit_code;
>
> extern exit_code call (const char **argv)
> diff --git a/plugins/sh/call.c b/plugins/sh/call.c
> index 2fa94d88..7d0f2b16 100644
> --- a/plugins/sh/call.c
> +++ b/plugins/sh/call.c
> @@ -1,5 +1,5 @@
> /* nbdkit
> - * Copyright (C) 2018-2020 Red Hat Inc.
> + * Copyright (C) 2018-2022 Red Hat Inc.
> *
> * Redistribution and use in source and binary forms, with or without
> * modification, are permitted provided that the following conditions are
> @@ -397,17 +397,47 @@ call3 (const char *wbuf, size_t wbuflen, /* sent to stdin (can be NULL) */
> return ret;
> }
>
> -static void
> -handle_script_error (const char *argv0, string *ebuf)
> +/* Normalize return codes and parse error string. */
> +static exit_code
> +handle_script_error (const char *argv0, string *ebuf, exit_code code)
> {
> int err;
> size_t skip = 0;
> char *p;
>
> - if (ebuf->len == 0) {
> + switch (code) {
> + case OK:
> + case MISSING:
> + case RET_FALSE:
> + /* Script successful. */
> + return code;
> +
> + case SHUTDOWN:
> + /* Use trigger, then handle empty ebuf specially below */
> + nbdkit_shutdown ();
> + break;
> +
> + case DISC_FORCE:
> + case DISC_SOFT:
> + /* Use trigger, then handle empty ebuf specially below */
> + nbdkit_disconnect (code == DISC_FORCE);
> + break;
> +
> + case ERROR:
> + default:
> + /* Error even if ebuf is empty */
> err = EIO;
> + goto parse;
Ugh, please don't use goto's like this. :/
(I can imagine that, if you rewrite this code according to my proposal
above, the parsing logic may become simpler to reach/retain.)
The rest looks OK (after briefly skimming it), it is affected by my
proposal though. In particular I notice "Noisy status 0 succeeds,
despite text to stderr" -- that might be useful to extend to the new
exit scenarios.
Laszlo
> + }
> +
> + assert (code >= SHUTDOWN && code <= DISC_SOFT);
> + if (ebuf->len == 0)
> + return OK;
> + err = ESHUTDOWN;
> +
> + parse:
> + if (ebuf->len == 0)
> goto no_error_message;
> - }
>
> /* Recognize the errno values that match NBD protocol errors */
> if (ascii_strncasecmp (ebuf->ptr, "EPERM", 5) == 0) {
> @@ -502,6 +532,7 @@ handle_script_error (const char *argv0, string *ebuf)
>
> /* Set errno. */
> errno = err;
> + return ERROR;
> }
>
> /* Call the script with parameters. Don't write to stdin or read from
> @@ -516,19 +547,7 @@ call (const char **argv)
> CLEANUP_FREE_STRING string ebuf = empty_vector;
>
> r = call3 (NULL, 0, &rbuf, &ebuf, argv);
> - switch (r) {
> - case OK:
> - case MISSING:
> - case RET_FALSE:
> - /* Script successful. */
> - return r;
> -
> - case ERROR:
> - default:
> - /* Error case. */
> - handle_script_error (argv[0], &ebuf);
> - return ERROR;
> - }
> + return handle_script_error (argv[0], &ebuf, r);
> }
>
> /* Call the script with parameters. Read from stdout and return the
> @@ -541,20 +560,10 @@ call_read (string *rbuf, const char **argv)
> CLEANUP_FREE_STRING string ebuf = empty_vector;
>
> r = call3 (NULL, 0, rbuf, &ebuf, argv);
> - switch (r) {
> - case OK:
> - case MISSING:
> - case RET_FALSE:
> - /* Script successful. */
> - return r;
> -
> - case ERROR:
> - default:
> - /* Error case. */
> + r = handle_script_error (argv[0], &ebuf, r);
> + if (r == ERROR)
> string_reset (rbuf);
> - handle_script_error (argv[0], &ebuf);
> - return ERROR;
> - }
> + return r;
> }
>
> /* Call the script with parameters. Write to stdin of the script.
> @@ -568,17 +577,5 @@ call_write (const char *wbuf, size_t wbuflen, const char **argv)
> CLEANUP_FREE_STRING string ebuf = empty_vector;
>
> r = call3 (wbuf, wbuflen, &rbuf, &ebuf, argv);
> - switch (r) {
> - case OK:
> - case MISSING:
> - case RET_FALSE:
> - /* Script successful. */
> - return r;
> -
> - case ERROR:
> - default:
> - /* Error case. */
> - handle_script_error (argv[0], &ebuf);
> - return ERROR;
> - }
> + return handle_script_error (argv[0], &ebuf, r);
> }
> diff --git a/tests/test-eval-disconnect.sh b/tests/test-eval-disconnect.sh
> new file mode 100755
> index 00000000..8427e6fd
> --- /dev/null
> +++ b/tests/test-eval-disconnect.sh
> @@ -0,0 +1,185 @@
> +#!/usr/bin/env bash
> +# nbdkit
> +# Copyright (C) 2022 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.
> +
> +# Check shutdown/disconnect behavior triggered by special status values
> +
> +source ./functions.sh
> +set -e
> +set -x
> +
> +requires_plugin eval
> +requires_nbdsh_uri
> +
> +sock=$(mktemp -u /tmp/nbdkit-test-sock.XXXXXX)
> +files="eval-disconnect.pid $sock"
> +rm -f $files
> +cleanup_fn rm -f $files
> +
> +# Start nbdkit with a plugin that fails writes according to the export
> +# name which must be numeric: a positive value leaves stderr empty, a
> +# non-positive one outputs EPERM first. Serve multiple clients.
> +serve()
> +{
> + rm -f $files
> + start_nbdkit -P eval-disconnect.pid -U $sock eval \
> + get_size=' echo 1024 ' \
> + open=' if test $3 -le 0; then \
> + echo EPERM > $tmpdir/err; echo $((-$3)); \
> + else \
> + : > $tmpdir/err; echo $3; \
> + fi ' \
> + flush=' exit 0 ' \
> + pwrite=' cat >/dev/null; cat $tmpdir/err >&2; exit $2 '
> +}
> +serve
> +
> +# Noisy status 0 succeeds, despite text to stderr
> +nbdsh -u "nbd+unix:///0?socket=$sock" -c - <<\EOF
> +h.pwrite(b"1", 0)
> +h.flush()
> +h.shutdown()
> +EOF
> +
> +# Silent status 1 fails; nbdkit turns lack of error into EIO
> +nbdsh -u "nbd+unix:///1?socket=$sock" -c - <<\EOF
> +import errno
> +try:
> + h.pwrite(b"1", 0)
> + assert False
> +except nbd.Error as ex:
> + assert ex.errnum == errno.EIO
> +h.flush()
> +h.shutdown()
> +EOF
> +
> +# Noisy status 1 fails with supplied EPERM
> +nbdsh -u "nbd+unix:///-1?socket=$sock" -c - <<\EOF
> +import errno
> +try:
> + h.pwrite(b"1", 0)
> + assert False
> +except nbd.Error as ex:
> + assert ex.errnum == errno.EPERM
> +h.flush()
> +h.shutdown()
> +EOF
> +
> +# Silent status 5 kills socket; libnbd detects dead socket as ENOTCONN
> +nbdsh -u "nbd+unix:///5?socket=$sock" -c - <<\EOF
> +import errno
> +try:
> + h.pwrite(b"1", 0)
> + assert False
> +except nbd.Error as ex:
> + assert ex.errnum == errno.ENOTCONN
> +assert h.aio_is_ready() is False
> +EOF
> +
> +# Noisy status 5 kills socket; libnbd detects dead socket as ENOTCONN
> +nbdsh -u "nbd+unix:///-5?socket=$sock" -c - <<\EOF
> +import errno
> +try:
> + h.pwrite(b"1", 0)
> + assert False
> +except nbd.Error as ex:
> + assert ex.errnum == errno.ENOTCONN
> +assert h.aio_is_ready() is False
> +EOF
> +
> +# Silent status 6 succeeds, but next command fails with ESHUTDOWN
> +nbdsh -u "nbd+unix:///6?socket=$sock" -c - <<\EOF
> +import errno
> +h.pwrite(b"1", 0)
> +try:
> + h.flush()
> + assert False
> +except nbd.Error as ex:
> + assert ex.errnum == errno.ESHUTDOWN
> +h.shutdown()
> +EOF
> +
> +# Noisy status 6 fails with supplied EPERM, next command fails with ESHUTDOWN
> +nbdsh -u "nbd+unix:///-6?socket=$sock" -c - <<\EOF
> +import errno
> +try:
> + h.pwrite(b"1", 0)
> + assert False
> +except nbd.Error as ex:
> + assert ex.errnum == errno.EPERM
> +try:
> + h.flush()
> + assert False
> +except nbd.Error as ex:
> + assert ex.errnum == errno.ESHUTDOWN
> +h.shutdown()
> +EOF
> +
> +# Silent status 4 kills the server. It is racy whether client sees a reply
> +# of success or sees the connection killed with libnbd giving ENOTCONN
> +nbdsh -u "nbd+unix:///4?socket=$sock" -c - <<\EOF
> +import errno
> +try:
> + h.pwrite(b"1", 0)
> +except nbd.Error as ex:
> + assert ex.errnum == errno.ENOTCONN
> +EOF
> +
> +# Server should die shortly, if not already dead at this point.
> +for (( i=0; i < 5; i++ )); do
> + kill -s 0 "$(cat eval-disconnect.pid)" || break
> + sleep 1
> +done
> +if [ $i = 5 ]; then
> + echo "nbdkit didn't exit fast enough"
> + exit 1
> +fi
> +
> +# Restart server; noisy status 4 races between EPERM or ENOTCONN
> +serve
> +nbdsh -u "nbd+unix:///-4?socket=$sock" -c - <<\EOF
> +import errno
> +try:
> + h.pwrite(b"1", 0)
> + assert False
> +except nbd.Error as ex:
> + assert ex.errnum == errno.EPERM or ex.errnum == errno.ENOTCONN
> +EOF
> +
> +# Server should die shortly, if not already dead at this point.
> +for (( i=0; i < 5; i++ )); do
> + kill -s 0 "$(cat eval-disconnect.pid)" || break
> + sleep 1
> +done
> +if [ $i = 5 ]; then
> + echo "nbdkit didn't exit fast enough"
> + exit 1
> +fi
>
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