Am 27.03.2015 um 18:12 hat Eric Blake geschrieben: > On 03/27/2015 09:36 AM, Michael Tokarev wrote: > > Wonder how to specify cache mode, or should I open these with proper > > O_DIRECT/O_SYNC/whatever? It looks like it's possible to change O_DIRECT > > at runtime but not O_SYNC. > > > > And the more interesting question is how to do that from shell. > > Redirections only get you so far in shell; you may need a wrapper C > program go get O_DIRECT and/or O_SYNC pre-set. Then again, if you use > QMP and pass over the Unix socket, you need a C program anyways.
O_DIRECT can be set with fcntl(), so qemu takes care of that. O_SYNC is completely unused on Linux these days, so that shouldn't be a problem either. (Other platforms use it as a misguided attempt of approximating O_DIRECT. We should really error out instead.) So if I'm not mistaken, just having one read-only and one read-write fd should be enough for any configuration in practice. Kevin
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