Libguestfs - Nov 2017 - [nbdkit PATCH 0/3] various nbdkit patches

Fixes for various issues found while implementing my nbd forwarder
plugin.  I'm okay if you choose to take some but not others; the
most important one is patch 3 which fixes a protocol violation
that makes it impossible for a client to try and recover from EIO
failures over a partially-flaky source block device.

Eric Blake (3):
  maint: Add emacs hint file
  maint: Add NBDKIT_GDB support to in-tree nbdkit script
  connections: Don't send NBD_CMD_READ payload on error

 .dir-locals.el    | 1 +
 nbdkit.in         | 9 +++++++--
 src/connections.c | 2 +-
 3 files changed, 9 insertions(+), 3 deletions(-)
 create mode 100644 .dir-locals.el

-- 
2.13.6

Let emacs know that this project prefers space rather than TAB
indentation.

Signed-off-by: Eric Blake <eblake@redhat.com>
---
 .dir-locals.el | 1 +
 1 file changed, 1 insertion(+)
 create mode 100644 .dir-locals.el

diff --git a/.dir-locals.el b/.dir-locals.el
new file mode 100644
index 0000000..c9c3aff
--- /dev/null
+++ b/.dir-locals.el
@@ -0,0 +1 @@
+((c-mode . ((indent-tabs-mode . nil))))
-- 
2.13.6

During development, it is handy to use the ./nbdkit script to
automatically pick up the just-built binaries without having
to install things; but using gdb on a script does not work.
Similar to how we already support $NBDKIT_VALGRIND, add support
for $NBDKIT_GDB; and also make the script robust to a value
of $prefix inherited from the environment.

Signed-off-by: Eric Blake <eblake@redhat.com>
---
 nbdkit.in | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/nbdkit.in b/nbdkit.in
index 167d512..6be89ec 100644
--- a/nbdkit.in
+++ b/nbdkit.in
@@ -99,11 +99,16 @@ if [ $verbose ]; then
     echo $b/src/nbdkit "${args[@]}"
 fi

+prefix # If NBDKIT_VALGRIND=1 is set in the environment, then we run
 # the program under valgrind.  This is used by the tests.
+# Similarly, if NBDKIT_GDB=1 is set in the environment, we run
+# the program under gdb, useful during development.
 if [ "$NBDKIT_VALGRIND" ]; then
-    valgrind="@VALGRIND@ --vgdb=no --leak-check=full --error-exitcode=119
--suppressions=$s/valgrind-suppressions --trace-children=no
--child-silent-after-fork=yes --run-libc-freeres=no"
+    prefix="@VALGRIND@ --vgdb=no --leak-check=full --error-exitcode=119
--suppressions=$s/valgrind-suppressions --trace-children=no
--child-silent-after-fork=yes --run-libc-freeres=no"
+elif [ "$NBDKIT_GDB" ]; then
+    prefix="gdb --args"
 fi

 # Run the final command.
-exec $valgrind $b/src/nbdkit "${args[@]}"
+exec $prefix $b/src/nbdkit "${args[@]}"
-- 
2.13.6

The NBD spec was clarified to state that a payload for NBD_CMD_READ
must NOT be sent unless the error field is zero (see
https://github.com/NetworkBlockDevice/nbd/commit/e6c6fb39);
doing this makes us compatible with nbd-server and qemu-nbd.

Signed-off-by: Eric Blake <eblake@redhat.com>
---
 src/connections.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/connections.c b/src/connections.c
index 8d65e2a..46609f0 100644
--- a/src/connections.c
+++ b/src/connections.c
@@ -1016,7 +1016,7 @@ recv_request_send_reply (struct connection *conn)
   }

   /* Send the read data buffer. */
-  if (cmd == NBD_CMD_READ) {
+  if (cmd == NBD_CMD_READ && !error) {
     r = conn->send (conn, buf, count);
     if (r == -1) {
       nbdkit_error ("write data: %m");
-- 
2.13.6

Thanks, I pushed this series.

Rich.

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