qemu-io: Don't die on second open

Most callback commands in qemu-io return 0 to keep the interpreter
loop running, or 1 to quit immediately.  However, open_f() just
passed through the return value of openfile(), which has different
semantics of returning 0 if a file was opened, or 1 on any failure.

As a result of mixing the return semantics, we are forcing the
qemu-io interpreter to exit early on any failures, which is rather
annoying when some of the failures are obviously trying to give
the user a hint of how to proceed (if we didn't then kill qemu-io
out from under the user's feet):

$ qemu-io
qemu-io> open foo
qemu-io> open foo
file open already, try 'help close'
$ echo $?
0

In general, we WANT openfile() to report failures, since it is the
function used in the form 'qemu-io -c "$something" no_such_file'
for performing one or more -c options on a single file, and it is
not worth attempting $something if the file itself cannot be opened.
So the solution is to fix open_f() to always return 0 (when we are
in interactive mode, even failure to open should not end the
session), and save the return value of openfile() for command line
use in main().

Note, however, that we do have some qemu-iotests that do 'qemu-io
-c "open file" -c "$something"'; such tests will now proceed to
attempt $something whether or not the open succeeded, the same way
as if the two commands had been attempted in interactive mode.  As
such, the expected output for those tests has to be modified.  But it
also means that it is now possible to use -c close and have a single
qemu-io command line operate on more than one file even without
using interactive mode.  Although the '-c open' action is a subtle
change in behavior, remember that qemu-io is for debugging purposes,
so as long as it serves the needs of qemu-iotests while still being
reasonable for interactive use, it should not be a problem that we
are changing tests to the new behavior.

This has been awkward since at least as far back as commit
e3aff4f, in 2009.

Signed-off-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Fam Zheng <famz@redhat.com>
Reviewed-by: John Snow <jsnow@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/tests/qemu-iotests/060.out b/tests/qemu-iotests/060.out
index 3bc14616be..5ca3af491f 100644
--- a/tests/qemu-iotests/060.out
+++ b/tests/qemu-iotests/060.out
@@ -21,6 +21,7 @@ Format specific information:
     refcount bits: 16
     corrupt: true
 can't open device TEST_DIR/t.IMGFMT: IMGFMT: Image is corrupt; cannot be opened read/write
+no file open, try 'help open'
 read 512/512 bytes at offset 0
 512 bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)