On 08/22/2013 01:31 PM, Alex Bligh wrote: > > > --On 22 August 2013 11:57:56 -0600 Eric Blake <ebl...@redhat.com> wrote: > >> # define O_DIRECT 0 >> >> so that the rest of the code can just blindly use open(...,|O_DIRECT) >> (provided, of course, that not having O_DIRECT semantics is not >> fatal...). If that is done, then this #ifdef will always be true... > > I think this is undesirable as the result of opening without O_DIRECT > when you really wanted O_DIRECT could be subtle data corruption due > to unexpected caching. Is an error not more appropriate here than > proceeding regardless?
As I said in the surrounding text you snipped: > > On some other projects I've worked with (hello gnulib!), the > compatibility headers do: ... > > But enough of that side diversion - that one #define of O_DIRECT is not > related to the file you are touching. Qemu doesn't define O_DIRECT to 0 for the mere sake of compilation, and I'm not arguing that it should. I was more making sure that this patch was correct, by reassuring myself the policies that qemu uses for O_DIRECT (and since I demonstrated that other projects have other policies). As to whether other projects may have a bug when using O_DIRECT being 0, it is a problem for those projects to deal with. Besides, O_DIRECT is a non-POSIX extension, so anyone using it already has non-portability issues to think about, regardless of whether the fallback for platforms that lack it is done by always defining to 0 or always using #ifdef guards. Thus, my diversion about other projects using O_DIRECT as 0 is a non-issue. -- Eric Blake eblake redhat com +1-919-301-3266 Libvirt virtualization library http://libvirt.org
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