Re: dd PATCH: add conv=direct

[Paul Eggert]

Jim Meyering <address@hidden> writes:

>>> > http://oss.oracle.com/projects/ocfs/dist/files/source/RHAT/RHAS3/coreutils-4.5.3-33.src.rpm

I briefly looked at the following patches in that RPM:

coreutils-4.5.3-O_DIRECT-NFS.patch
coreutils-4.5.3-O_DIRECT-dd.patch
coreutils-4.5.3-O_DIRECT-valloc.patch
coreutils-4.5.3-o_direct-copy-valloc.patch
coreutils-4.5.3-o_direct.patch

and I found the following differences between those ideas and what's
in coreutils CVS right now:

* Coreutils dd simply aligns the I/O buffers to getpagesize()
  boundaries, 4.5.3-33 has a complicated alignment strategy that I
  don't fully follow, but which seems to do the same thing.
  (There may be some differences if I/O errors occur; is that
  the point?)

* 4.5.3-33 aligns buffers to page size boundaries in copy.c.
  This looks to me like it's worth doing (independently of O_DIRECT),
  so I'll propose a patch along those lines via separate email
  to bug-coreutils.

* cp, mv, and md5sum have --o_direct options.  I'm not convinced that
  md5sum needs this (why not all the other commands that read files,
  too, while you're at it? cat, say?) but perhaps cp and mv should
  have it (what are the application areas here?).  Also, option names
  should not have underscores, so I'd suggest --direct (or perhaps
  --direct-io) as a better name for this sort of option.

* The dd options are spelled differently, e.g.:

  dd ibs=512 obs=1024 iflags=direct oflags=direct (coreutils CVS)
  dd --o_direct=512,1024   (4.5.3-33)

  Here I prefer the coreutils CVS version as it's a bit more orthogonal.