Paul Eggert <[EMAIL PROTECTED]> wrote: > > Andrew Morton <[EMAIL PROTECTED]> 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,
And when the read fails. > since conv=direct can't be implemented. The basic idea > is that on systems that lack direct I/O, conv=direct should fail. I think that's best. It's a bit user-unfriendly, but a silent fallback is misleading. It might be acceptable to print a warning, then fall back. > 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"? solaris directio(DIRECTIO_ON) is a hint only. If the system cannot perform the uncached zerocopy then it will fall back to buffered IO. Solaris will perform direct-IO "when the application's buffer is aligned on a two-byte (short) boundary, the offset into the file is on a device sector boundary, and the size of the operation is a multiple of device sectors." On Linux you set direct-io with open(O_DIRECT) or fcntl(F_SETFL, O_DIRECT). If the filesystem doesn't support direct-io we will fail the open/fcntl attempt up-front in 2.6 only. If O_DIRECT was successfully set and the IO is not correctly aligned Linux will fail the relevant I/O attempt. Alignment requirements are: 2.4: page aligned on-disk and in-memory 2.6: device sector aligned on-disk and in-memory. I'd recomment that dd use getpagesize() alignment on-disk and in-memory. _______________________________________________ Bug-coreutils mailing list [EMAIL PROTECTED] http://mail.gnu.org/mailman/listinfo/bug-coreutils
