Re: [libvirt] [PATCH v2 06/10] virCommandWait: Propagate dryRunCallback return value properly

On 07/23/2018 04:01 AM, Michal Prívozník wrote: > On 07/17/2018 08:43 PM, John Ferlan wrote: >> >> >> On 07/04/2018 05:23 AM, Michal Privoznik wrote: >>> The documentation to virCommandWait() function states that if >>> @exitstatus is NULL and command finished with error -1 is >>> returned. In other words, if @dryRunCallback is set and returns >>> an error (by setting its @status argument to a nonzero value) we >>> must propagate this error properly honouring the documentation >>> (and also regular run). >>> >> >> That's not how I read virCommandWait: >> >> * Wait for the command previously started with virCommandRunAsync() >> * to complete. Return -1 on any error waiting for >> * completion. Returns 0 if the command >> * finished with the exit status set. If @exitstatus is NULL, then the >> * child must exit with status 0 for this to succeed. By default, >> * a non-NULL @exitstatus contains the normal exit status of the child >> * (death from a signal is treated as execution error); but if >> * virCommandRawStatus() was used, it instead contains the raw exit >> * status that the caller must then decipher using WIFEXITED() and friends. >> >> perhaps the author (danpb) of commit id 7b3f1f8c3 would be able to say >> for sure... >> >> I only see -1 being returned "on any error waiting for completion". >> Filling @exitstatus with @dryRunStatus is reasonable since it is >> initialized to 0 in virCommandRunAsync and is what is passed to >> @dryRunCallback and thus only changed as a result of running >> @dryRunCallback. >> >> It has nothing to do with virCommandWait AFAICT. > > So there are two ways how virCommandWait() can be called. The first is > with @exitstatus being non-NULL. In this case, error is returned iff > there was an error fetching command's exit status (e.g. because > virProcessWait() failed). The second way is to call virCommandWait() > with NULL in which case the function fails for all the cases in the > first case plus if the command exit status is not zero. This is > documented in docs/internals/command.html#async: > > > As with virCommandRun, the status arg for virCommandWait can be > omitted, in which case it will validate that exit status is zero and > raise an error if not. > > Let's put aside dry run case for a while. Imagine /bin/false was started > asynchronously and control now reaches virCommandWait(cmd, NULL). What > do you think should be expected return value? I'd expect "Child process > (%) unexpected..." error message and return -1. However, this is not the > case if dry run callback sets an error. > > Michal > Was /bin/false run successfully? It returns 1 (non zero). Isn't that expected? Did virCommandWait fail to wait for /bin/false to return?

If someone wants the status from virCommandRunAsync, then they need to pass the @exitstatus in; otherwise, the command itself actually ran to completion and returned the expected result. If I want to know that result, then I should use the proper mechanism which is to pass @exitstatus. The virCommandWait didn't fail (regardless of DryRun or not) to wait for completion, so returning -1 because the underlying command "failed" seems to be outside it's scope of purpose.