On 05/31/2017 09:18 AM, Max Reitz wrote: > On 2017-05-24 22:28, Eric Blake wrote: >> 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 $? >> 0 >> >> Meanwhile, we WANT openfile() to report failures, as it is the >> way that 'qemu-io -c "$something" no_such_file' knows to exit >> early rather than attempting $something. So the solution is to >> fix open_f() to always return 0 (when we are in interactive mode, >> even failure to open should not end the session), and save the >> return value of openfile() for command line use in main(). >> >> This has been awkward since at least as far back as commit >> e3aff4f, in 2009. >> >> Signed-off-by: Eric Blake <ebl...@redhat.com> > > This still makes qemu-io -c "$something" no_such_file fail, right. But > now qemu-io -c "open no_such_file" -c "$something" will execute > $something; and I'm not sure we can convert all -c open users to not use > that command (maybe we can, now that we have --image-opts).
Oh, so we do have some uses of -c "open..." -c "$something" (iotest 103 for example). What happens during "$something" if there was no file currently open? It may be a command-by-command behavior. But as long as we get graceful secondary failures rather than crashes for those subsequent $somethings, we may be okay. > > I don't think it's absolutely necessary for -c open to exit on error, > but you seem to do, if I understand your penultimate paragraph > correctly. :-) I don't think it's absolutely necessary either. You're right that this patch is just worried about 'qemu-img name', not 'qemu-img -c "open name"'. So maybe all I need to do is update the commit message to document that the change in semantics to -c "open..." is a side-effect, that may or may not be changed in a followup patch? -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3266 Virtualization: qemu.org | libvirt.org
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