On Fri, Apr 01, 2011 at 11:19:07AM -0400, Ted Ts'o wrote: > The closest place that we have to any official documentation about > O_DIRECT semantics is the open(2) man page in the Linux manpages, and > it doesn't say anything about this. It does give a recommendation > against not mixing buffered and O_DIRECT accesses to the same file, > but it does promise that things will work in that case. (Even if it > does, do we really want to make the promise that it will always work?) No, we do not. Some OSes will silently turn buffered I/O into direct I/O if another file already has it opened O_DIRECT. Some OSes will fail the write, or the open, or both, if it doesn't match the mode of an existing fd. Some just leave O_DIRECT and buffered access inconsistent. I think that Linux should strive to make the mixed buffered/direct case work; it's the nicest thing we can do. But we should not promise it. Joel -- Life's Little Instruction Book #24 "Drink champagne for no reason at all." http://www.jlbec.org/ jlbec@xxxxxxxxxxxx -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
