• Eric Blake's avatar
    maint: Fix macros with broken 'do/while(0); ' usage · 2562755e
    Eric Blake authored
    The point of writing a macro embedded in a 'do { ... } while (0)'
    loop (particularly if the macro has multiple statements or would
    otherwise end with an 'if' statement) is so that the macro can be
    used as a drop-in statement with the caller supplying the
    trailing ';'.  Although our coding style frowns on brace-less 'if':
      if (cond)
        statement;
      else
        something else;
    that is the classic case where failure to use do/while(0) wrapping
    would cause the 'else' to pair with any embedded 'if' in the macro
    rather than the intended outer 'if'.  But conversely, if the macro
    includes an embedded ';', then the same brace-less coding style
    would now have two statements, making the 'else' a syntax error
    rather than pairing with the outer 'if'.  Thus, even though our
    coding style with required braces is not impacted, ending a macro
    with ';' makes our code harder to port to projects that use
    brace-less styles.
    
    The change should have no semantic impact.  I was not able to
    fully compile-test all of the changes (as some of them are
    examples of the ugly bit-rotting debug print statements that are
    completely elided by default, and I didn't want to recompile
    with the necessary -D witnesses - cleaning those up is left as a
    bite-sized task for another day); I did, however, audit that for
    all files touched, all callers of the changed macros DID supply
    a trailing ';' at the callsite, and did not appear to be used
    as part of a brace-less conditional.
    
    Found mechanically via: $ git grep -B1 'while (0);' | grep -A1 \\\\
    Signed-off-by: 's avatarEric Blake <eblake@redhat.com>
    Acked-by: 's avatarCornelia Huck <cohuck@redhat.com>
    Reviewed-by: 's avatarMichael S. Tsirkin <mst@redhat.com>
    Acked-by: 's avatarDr. David Alan Gilbert <dgilbert@redhat.com>
    Message-Id: <20171201232433.25193-7-eblake@redhat.com>
    Reviewed-by: 's avatarJuan Quintela <quintela@redhat.com>
    Signed-off-by: 's avatarPaolo Bonzini <pbonzini@redhat.com>
    2562755e
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