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    SubjectRe: [PATCH 18/16] implement posix O_SYNC and O_DSYNC semantics
    On Sep 10, 2009  22:25 +0200, Christoph Hellwig wrote:
    > +/*
    > + * Before Linux 2.6.32 only O_DSYNC semantics were implemented, but using
    > + * the O_SYNC flag. We continue to use the existing numerical value
    > + * for O_DSYNC semantics now, but using the correct symbolic name for it.
    > + * This new value is used to request true Posix O_SYNC semantics. It is
    > + * defined in this strange way to make sure applications compiled against
    > + * new headers get at least O_DSYNC semantics on older kernels.
    > + *
    > + * This has the nice side-effect that we can simply test for O_DSYNC
    > + * wherever we do not care if O_DSYNC or O_SYNC is used.
    > +
    > + * Note: __O_SYNC must never be used directly.

    Doesn't it make sense that applications that actually know what they are
    doing may want to start using __O_SYNC directly at some point in the
    future? It makes sense to code the kernel to handle both of these flags
    appropriately (i.e. if __O_SYNC is set, but O_DSYNC is not then treat
    this as the proper "O_SYNC").

    > Index: linux-2.6/arch/alpha/include/asm/fcntl.h
    > ===================================================================
    > --- linux-2.6.orig/arch/alpha/include/asm/fcntl.h 2009-09-10 16:31:47.720004025 -0300
    > +++ linux-2.6/arch/alpha/include/asm/fcntl.h 2009-09-10 16:33:55.087294444 -0300
    > #define O_CLOEXEC 010000000 /* set close_on_exec */
    > +#define __O_SYNC 010000000

    These two flags have the same value...

    Cheers, Andreas
    --
    Andreas Dilger
    Sr. Staff Engineer, Lustre Group
    Sun Microsystems of Canada, Inc.



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