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    SubjectRe: dd PATCH: add conv=direct
    On Tue, Apr 06, 2004 at 05:33:26PM -0700, Andrew Morton wrote:
    > Andy Isaacson <adi@hexapodia.org> wrote:
    > > dd(1) is convenient for this purpose, but is lacking a method
    > > to force O_DIRECT. The enclosed patch adds a "conv=direct" flag to
    > > enable this usage.
    >
    > This would be rather nice to have. You'll need to ensure that the data
    > is page-aligned in memory.

    So, some confusion on my part about O_DIRECT: I can't get O_DIRECT to
    work on ext3, at all, on 2.4.25 -- open(O_DIRECT) succeeds, but the write
    returns EINVAL. Same code works fine when writing to a block device.
    If the problem is that ext3 can't support O_DIRECT, why does the open
    succeed?

    > While you're there, please add an fsync-before-closing option.

    Easy enough. How does this look? Note that C_TWOBUFS ensures the
    output buffer is getpagesize()-aligned.

    The next feature to add would be OpenBSD-style "KB/s" reporting. I'm
    not going there.

    -andy

    2004-04-07 Andy Isaacson <adi@hexapodia.org>

    * add conv=direct and conv=fsync options.

    diff -ur coreutils-5.0.91/doc/coreutils.texi coreutils-5.0.91-adi/doc/coreutils.texi
    --- coreutils-5.0.91/doc/coreutils.texi 2003-09-04 16:26:51.000000000 -0500
    +++ coreutils-5.0.91-adi/doc/coreutils.texi 2004-04-07 11:26:36.000000000 -0500
    @@ -6373,6 +6373,16 @@
    Pad every input block to size of @samp{ibs} with trailing zero bytes.
    When used with @samp{block} or @samp{unblock}, pad with spaces instead of
    zero bytes.
    +
    +@item fsync
    +@opindex fsync
    +Call @samp{fsync(2)} on the output file before exiting. This ensures
    +that the file data is written to permanent store.
    +
    +@item direct
    +@opindex direct
    +Open the output file with O_DIRECT, avoiding (on Linux) using the buffer
    +cache.
    @end table

    @end table
    diff -ur coreutils-5.0.91/src/dd.c coreutils-5.0.91-adi/src/dd.c
    --- coreutils-5.0.91/src/dd.c 2003-07-25 02:43:09.000000000 -0500
    +++ coreutils-5.0.91-adi/src/dd.c 2004-04-07 11:45:23.000000000 -0500
    @@ -66,6 +66,9 @@
    /* Default input and output blocksize. */
    #define DEFAULT_BLOCKSIZE 512

    +/* XXX hack */
    +#define HAVE_O_DIRECT 1
    +
    /* Conversions bit masks. */
    #define C_ASCII 01
    #define C_EBCDIC 02
    @@ -78,6 +81,8 @@
    #define C_NOERROR 0400
    #define C_NOTRUNC 01000
    #define C_SYNC 02000
    +#define C_FSYNC 010000
    +#define C_DIRECT 020000
    /* Use separate input and output buffers, and combine partial input blocks. */
    #define C_TWOBUFS 04000

    @@ -162,6 +167,10 @@
    {"noerror", C_NOERROR}, /* Ignore i/o errors. */
    {"notrunc", C_NOTRUNC}, /* Do not truncate output file. */
    {"sync", C_SYNC}, /* Pad input records to ibs with NULs. */
    + {"fsync", C_FSYNC}, /* call fsync(2) before closing output file */
    +#ifdef HAVE_O_DIRECT
    + {"direct", C_DIRECT | C_TWOBUFS}, /* open files with O_DIRECT */
    +#endif
    {NULL, 0}
    };

    @@ -1190,6 +1199,11 @@
    = (O_CREAT
    | (seek_records || (conversions_mask & C_NOTRUNC) ? 0 : O_TRUNC));

    +#if HAVE_O_DIRECT
    + if (conversions_mask & C_DIRECT)
    + opts |= O_DIRECT;
    +#endif
    +
    /* Open the output file with *read* access only if we might
    need to read to satisfy a `seek=' request. If we can't read
    the file, go ahead with write-only access; it might work. */
    @@ -1240,5 +1254,11 @@

    exit_status = dd_copy ();

    + if (conversions_mask & C_FSYNC)
    + {
    + if (fsync (STDOUT_FILENO) != 0)
    + error(0, errno, _("cannot fsync %s"), quote (output_file));
    + }
    +
    quit (exit_status);
    }
    -
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