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[Libguestfs] [nbdkit PATCH 2/2] server: Add --mask-handshake option for integration testing



Similar to --no-sr, it can be handy for testing a client
implementation to have a server that can easily be forced into older
behaviors, without having to recompile a one-off hack into a server or
dig up an older server binary that lacked a newer feature.

To see the patch in action, try things like:
$ ./nbdkit -U - -fv --mask-handshake=0 null \
  --run 'qemu-nbd --list -k $unixsocket'

Signed-off-by: Eric Blake <eblake redhat com>
---
 docs/nbdkit-protocol.pod             | 25 ++++++++++++++++++-----
 docs/synopsis.txt                    |  2 +-
 server/internal.h                    |  1 +
 server/options.h                     |  2 ++
 server/main.c                        | 30 ++++++++++++++++++----------
 server/protocol-handshake-newstyle.c |  4 ++--
 6 files changed, 45 insertions(+), 19 deletions(-)

diff --git a/docs/nbdkit-protocol.pod b/docs/nbdkit-protocol.pod
index 3ae89063..272f4e5b 100644
--- a/docs/nbdkit-protocol.pod
+++ b/docs/nbdkit-protocol.pod
@@ -4,8 +4,8 @@ nbdkit - which parts of the NBD protocol nbdkit supports

 =head1 SYNOPSIS

- nbdkit [-n|--newstyle] [--no-sr] [-o|--oldstyle] [-e|--exportname EXPORTNAME]
-        [...]
+ nbdkit [-n|--newstyle] [--mask-handshake MASK] [--no-sr] [-o|--oldstyle]
+        [-e|--exportname EXPORTNAME] [...]

 =head1 DESCRIPTION

@@ -24,15 +24,30 @@ newstyle protocol is better in every respect than the oldstyle
 protocol and you should prefer it if possible.  The newstyle protocol
 also includes an extension where a client may request structured
 replies for even more capabilities, such as sparse reads or obtaining
-block status.
+block status.  By default, nbdkit advertises as many features as it
+can support (in some cases, this can be limited by what callbacks the
+plugin handles), even if the client does not negotiate to use all
+advertised features.

 Use the I<-e> or I<--exportname> flag to set the optional exportname
 for the newstyle protocol.

-Use the I<--no-sr> flag to force the newstyle protocol to decline any
-client request for structured replies.
+Nbdkit also includes some options that are useful mainly when
+performing integration tests, for proving whether clients have sane
+fallback behavior when dealing various older servers permitted by the
+NBD protocol.  Use the I<--no-sr> flag to force the newstyle protocol
+to decline any client request for structured replies.  Use the
+I<--mask-handshake> parameter to mask off particular global features
+which are advertised during new-style handshake (defaulting to all
+supported bits set).  Clearing bit 0 (the low order bit) limits a
+client to using just C<NBD_OPT_EXPORT_NAME> (and is incompatible with
+TLS or structured replies); clearing bit 1 causes the handshake to
+send more padding bytes in response to C<NBD_OPT_EXPORT_NAME>.  Other
+bits in the mask will only have an effect if the NBD protocol is
+extended in the future to define other global bits.

 Use the I<-o> or I<--oldstyle> flag to force the oldstyle protocol.
+In this mode, I<--no-sr> and I<--mask-handshake> have no effect.

 =head2 Common clients and the protocol they require

diff --git a/docs/synopsis.txt b/docs/synopsis.txt
index 04cd136d..5fc57fd1 100644
--- a/docs/synopsis.txt
+++ b/docs/synopsis.txt
@@ -3,7 +3,7 @@ nbdkit [-D|--debug PLUGIN|FILTER.FLAG=N]
        [--filter FILTER ...] [-f|--foreground]
        [-g|--group GROUP] [-i|--ipaddr IPADDR]
        [--log stderr|syslog]
-       [-n|--newstyle] [--no-sr] [-o|--oldstyle]
+       [-n|--newstyle] [--mask-handshake MASK] [--no-sr] [-o|--oldstyle]
        [-P|--pidfile PIDFILE]
        [-p|--port PORT] [-r|--readonly]
        [--run CMD] [-s|--single] [--selinux-label LABEL]
diff --git a/server/internal.h b/server/internal.h
index 9314e8ff..5da3e3c3 100644
--- a/server/internal.h
+++ b/server/internal.h
@@ -90,6 +90,7 @@ extern const char *exportname;
 extern bool foreground;
 extern const char *ipaddr;
 extern enum log_to log_to;
+extern unsigned mask_handshake;
 extern bool newstyle;
 extern bool no_sr;
 extern const char *port;
diff --git a/server/options.h b/server/options.h
index a69f413a..c74e0b8b 100644
--- a/server/options.h
+++ b/server/options.h
@@ -46,6 +46,7 @@ enum {
   FILTER_OPTION,
   LOG_OPTION,
   LONG_OPTIONS_OPTION,
+  MASK_HANDSHAKE_OPTION,
   NO_SR_OPTION,
   RUN_OPTION,
   SELINUX_LABEL_OPTION,
@@ -74,6 +75,7 @@ static const struct option long_options[] = {
   { "ipaddr",           required_argument, NULL, 'i' },
   { "log",              required_argument, NULL, LOG_OPTION },
   { "long-options",     no_argument,       NULL, LONG_OPTIONS_OPTION },
+  { "mask-handshake",   required_argument, NULL, MASK_HANDSHAKE_OPTION },
   { "new-style",        no_argument,       NULL, 'n' },
   { "newstyle",         no_argument,       NULL, 'n' },
   { "no-sr",            no_argument,       NULL, NO_SR_OPTION },
diff --git a/server/main.c b/server/main.c
index 22cf8d33..d433c1fa 100644
--- a/server/main.c
+++ b/server/main.c
@@ -67,6 +67,7 @@ const char *exportname;         /* -e */
 bool foreground;                /* -f */
 const char *ipaddr;             /* -i */
 enum log_to log_to = LOG_TO_DEFAULT; /* --log */
+unsigned mask_handshake = ~0U;  /* --mask-handshake */
 bool newstyle = true;           /* false = -o, true = -n */
 bool no_sr;                     /* --no-sr */
 char *pidfile;                  /* -P */
@@ -148,6 +149,7 @@ main (int argc, char *argv[])
   } *filter_filenames = NULL;
   size_t i;
   const char *magic_config_key;
+  char *end;

   /* Refuse to run if stdin/out/err are closed, whether or not -s is used. */
   if (fcntl (STDERR_FILENO, F_GETFL) == -1) {
@@ -348,6 +350,16 @@ main (int argc, char *argv[])
       ipaddr = optarg;
       break;

+    case MASK_HANDSHAKE_OPTION:
+      errno = 0;
+      mask_handshake = strtoul (optarg, &end, 0);
+      if (errno || *end) {
+        fprintf (stderr, "%s: cannot parse '%s' into mask-handshake\n",
+                 program_name, optarg);
+        exit (EXIT_FAILURE);
+      }
+      break;
+
     case 'n':
       newstyle = true;
       break;
@@ -389,18 +401,14 @@ main (int argc, char *argv[])
       break;

     case 't':
-      {
-        char *end;
-
-        errno = 0;
-        threads = strtoul (optarg, &end, 0);
-        if (errno || *end) {
-          fprintf (stderr, "%s: cannot parse '%s' into threads\n",
-                   program_name, optarg);
-          exit (EXIT_FAILURE);
-        }
-        /* XXX Worth a maximimum limit on threads? */
+      errno = 0;
+      threads = strtoul (optarg, &end, 0);
+      if (errno || *end) {
+        fprintf (stderr, "%s: cannot parse '%s' into threads\n",
+                 program_name, optarg);
+        exit (EXIT_FAILURE);
       }
+      /* XXX Worth a maximimum limit on threads? */
       break;

     case 'U':
diff --git a/server/protocol-handshake-newstyle.c b/server/protocol-handshake-newstyle.c
index 486d416f..9801f7c2 100644
--- a/server/protocol-handshake-newstyle.c
+++ b/server/protocol-handshake-newstyle.c
@@ -673,7 +673,7 @@ protocol_handshake_newstyle (struct connection *conn)
   struct new_handshake handshake;
   uint16_t gflags;

-  gflags = NBD_FLAG_FIXED_NEWSTYLE | NBD_FLAG_NO_ZEROES;
+  gflags = (NBD_FLAG_FIXED_NEWSTYLE | NBD_FLAG_NO_ZEROES) & mask_handshake;

   debug ("newstyle negotiation: flags: global 0x%x", gflags);

@@ -694,7 +694,7 @@ protocol_handshake_newstyle (struct connection *conn)
   /* ... which we check for accuracy. */
   debug ("newstyle negotiation: client flags: 0x%x", conn->cflags);
   if (conn->cflags & ~gflags) {
-    nbdkit_error ("client requested unknown flags 0x%x", conn->cflags);
+    nbdkit_error ("client requested unexpected flags 0x%x", conn->cflags);
     return -1;
   }

-- 
2.21.0


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