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qemu-nbd: Allow users to adjust handshake limit

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Although defaulting the handshake limit to 10 seconds was a nice QoI
change to weed out intentionally slow clients, it can interfere with
integration testing done with manual NBD_OPT commands over 'nbdsh
--opt-mode'.  Expose a command line option to allow the user to alter
the timeout away from the default.  This option is unlikely to be used
in enough scenarios to warrant a short option letter.

The option --handshake-limit intentionally differs from the name of
the constant added in commit fb1c2aaa98 (limit instead of max_secs)
and the QMP name to be added in the next commit; this is because
typing a longer command-line name is undesirable and there is
sufficient --help text to document the units.

Signed-off-by: Eric Blake <eblake@redhat.com>
Message-ID: <20250203222722.650694-5-eblake@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
This commit is contained in:
Eric Blake 2025-02-03 16:26:06 -06:00
parent ffaf7f0376
commit 617017f8dc
2 changed files with 31 additions and 15 deletions
Download patch file Download diff file Expand all files Collapse all files

5
docs/tools/qemu-nbd.rst
View file

@ -156,6 +156,11 @@ driver options if :option:`--image-opts` is specified.
Set the NBD volume export description, as a human-readable
string.
.. option:: --handshake-limit=N
Set the timeout for a client to successfully complete its handshake
to N seconds (default 10), or 0 for no limit.
.. option:: -L, --list
Connect as a client and list all details about the exports exposed by

15
qemu-nbd.c
View file

@ -70,6 +70,7 @@
#define QEMU_NBD_OPT_PID_FILE 265
#define QEMU_NBD_OPT_SELINUX_LABEL 266
#define QEMU_NBD_OPT_TLSHOSTNAME 267
#define QEMU_NBD_OPT_HANDSHAKE_LIMIT 268
#define MBR_SIZE 512
@ -80,6 +81,7 @@ static int nb_fds;
static QIONetListener *server;
static QCryptoTLSCreds *tlscreds;
static const char *tlsauthz;
static int handshake_limit = NBD_DEFAULT_HANDSHAKE_MAX_SECS;
static void usage(const char *name)
{
@ -101,6 +103,7 @@ static void usage(const char *name)
" -v, --verbose display extra debugging information\n"
" -x, --export-name=NAME expose export by name (default is empty string)\n"
" -D, --description=TEXT export a human-readable description\n"
" --handshake-limit=N limit client's handshake to N seconds (default 10)\n"
"\n"
"Exposing part of the image:\n"
" -o, --offset=OFFSET offset into the image\n"
@ -390,8 +393,7 @@ static void nbd_accept(QIONetListener *listener, QIOChannelSocket *cioc,
nb_fds++;
nbd_update_server_watch();
/* TODO - expose handshake timeout as command line option */
nbd_client_new(cioc, NBD_DEFAULT_HANDSHAKE_MAX_SECS,
nbd_client_new(cioc, handshake_limit,
tlscreds, tlsauthz, nbd_client_closed, NULL);
}
@ -569,6 +571,8 @@ int main(int argc, char **argv)
{ "object", required_argument, NULL, QEMU_NBD_OPT_OBJECT },
{ "export-name", required_argument, NULL, 'x' },
{ "description", required_argument, NULL, 'D' },
{ "handshake-limit", required_argument, NULL,
QEMU_NBD_OPT_HANDSHAKE_LIMIT },
{ "tls-creds", required_argument, NULL, QEMU_NBD_OPT_TLSCREDS },
{ "tls-hostname", required_argument, NULL, QEMU_NBD_OPT_TLSHOSTNAME },
{ "tls-authz", required_argument, NULL, QEMU_NBD_OPT_TLSAUTHZ },
@ -815,6 +819,13 @@ int main(int argc, char **argv)
case QEMU_NBD_OPT_SELINUX_LABEL:
selinux_label = optarg;
break;
case QEMU_NBD_OPT_HANDSHAKE_LIMIT:
if (qemu_strtoi(optarg, NULL, 0, &handshake_limit) < 0 ||
handshake_limit < 0) {
error_report("Invalid handshake limit '%s'", optarg);
exit(EXIT_FAILURE);
}
break;
}
}