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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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