[Qemu-block] [PATCH v3 1/4] qemu-io: Don't die on second open

[Eric Blake]

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; 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.

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

Signed-off-by: Eric Blake <address@hidden>
Reviewed-by: Fam Zheng <address@hidden>

---
v3: tweak commit message to distinguish that '-c open' has a subtle
new behavior from the command line
v2: fix open_f(), not openfile()
---
 qemu-io.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/qemu-io.c b/qemu-io.c
index 8e38b28..8074656 100644
--- a/qemu-io.c
+++ b/qemu-io.c
@@ -230,13 +230,14 @@ static int open_f(BlockBackend *blk, int argc, char 
**argv)
     qemu_opts_reset(&empty_opts);

     if (optind == argc - 1) {
-        return openfile(argv[optind], flags, writethrough, force_share, opts);
+        openfile(argv[optind], flags, writethrough, force_share, opts);
     } else if (optind == argc) {
-        return openfile(NULL, flags, writethrough, force_share, opts);
+        openfile(NULL, flags, writethrough, force_share, opts);
     } else {
         QDECREF(opts);
-        return qemuio_command_usage(&open_cmd);
+        qemuio_command_usage(&open_cmd);
     }
+    return 0;
 }

 static int quit_f(BlockBackend *blk, int argc, char **argv)
-- 
2.9.4