Re: dd PATCH: add conv=direct

[Paul Eggert]

Andrew Morton <address@hidden> writes:

> In 2.6 we do the check at open() and fcntl() time.  In 2.4 we don't
> fail until the actual I/O attempt.

This raises the issue of what "dd conv=direct" should do in 2.4
kernels.  I propose that it should report an error and exit, when the
write fails, since conv=direct can't be implemented.  The basic idea
is that on systems that lack direct I/O, conv=direct should fail.

Another issue with this patch: in Solaris, direct I/O is done by
invoking directio(DIRECTIO_ON); see
<http://docs.sun.com/db/doc/816-0213/6m6ne37so?q=directio&a=view>.
Is Solaris direct I/O a direct analog to Linux direct I/O, or are
there subtle differences in semantics that should be made visible to
the users of GNU "dd"?