--- Begin Message ---
Subject: |
[PATCH] dd: sparse conv flag |
Date: |
Sat, 23 Jul 2011 20:08:01 +0400 |
---
doc/coreutils.texi | 4 +++
src/dd.c | 22 +++++++++++++++-
tests/Makefile.am | 1 +
tests/dd/sparse | 70 ++++++++++++++++++++++++++++++++++++++++++++++++++++
4 files changed, 96 insertions(+), 1 deletions(-)
create mode 100755 tests/dd/sparse
diff --git a/doc/coreutils.texi b/doc/coreutils.texi
index 424446c..761c698 100644
--- a/doc/coreutils.texi
+++ b/doc/coreutils.texi
@@ -8127,6 +8127,10 @@ 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.
address@hidden sparse
address@hidden sparse
+Make sparse output file.
+
@end table
The following ``conversions'' are really file flags
diff --git a/src/dd.c b/src/dd.c
index 0824f6c..49847f5 100644
--- a/src/dd.c
+++ b/src/dd.c
@@ -126,7 +126,8 @@ enum
C_NOCREAT = 010000,
C_EXCL = 020000,
C_FDATASYNC = 040000,
- C_FSYNC = 0100000
+ C_FSYNC = 0100000,
+ C_SPARSE = 0200000
};
/* Status bit masks. */
@@ -268,6 +269,7 @@ static struct symbol_value const conversions[] =
{"sync", C_SYNC}, /* Pad input records to ibs with NULs. */
{"fdatasync", C_FDATASYNC}, /* Synchronize output data before finishing. */
{"fsync", C_FSYNC}, /* Also synchronize output metadata. */
+ {"sparse", C_SPARSE}, /* Make sparse output file. */
{"", 0}
};
@@ -533,6 +535,9 @@ Each CONV symbol may be:\n\
fsync likewise, but also write metadata\n\
"), stdout);
fputs (_("\
+ sparse make sparse output file\n\
+"), stdout);
+ fputs (_("\
\n\
Each FLAG symbol may be:\n\
\n\
@@ -985,6 +990,21 @@ iwrite (int fd, char const *buf, size_t size)
{
ssize_t nwritten;
process_signals ();
+ if (conversions_mask & C_SPARSE)
+ {
+ off_t seek_size = 0;
+ while (buf[total_written + seek_size] == 0)
+ ++seek_size;
+ if (seek_size)
+ {
+ off_t cur_off = 0;
+ cur_off = lseek(fd, seek_size, SEEK_CUR);
+ if (cur_off < 0)
+ break;
+ total_written += seek_size;
+ continue;
+ }
+ }
nwritten = write (fd, buf + total_written, size - total_written);
if (nwritten < 0)
{
diff --git a/tests/Makefile.am b/tests/Makefile.am
index ebd1b11..0f1376a 100644
--- a/tests/Makefile.am
+++ b/tests/Makefile.am
@@ -364,6 +364,7 @@ TESTS = \
dd/skip-seek \
dd/skip-seek2 \
dd/skip-seek-past-file \
+ dd/sparse \
dd/stderr \
dd/unblock \
dd/unblock-sync \
diff --git a/tests/dd/sparse b/tests/dd/sparse
new file mode 100755
index 0000000..f0e0806
--- /dev/null
+++ b/tests/dd/sparse
@@ -0,0 +1,70 @@
+#!/bin/sh
+# Ensure that dd conv=sparse works.
+
+# Copyright (C) 2003, 2005-2011 Free Software Foundation, Inc.
+
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+# GNU General Public License for more details.
+
+# You should have received a copy of the GNU General Public License
+# along with this program. If not, see <http://www.gnu.org/licenses/>.
+
+. "${srcdir=.}/init.sh"; path_prepend_ ../src
+print_ver_ dd
+
+# sometimes we may read less than 1M
+dd if=/dev/zero of=sample0 count=1 bs=1M 2> /dev/null || fail=1
+[ "`stat -c %s sample0`" = "1048576" ] || fail=1
+dd if=/dev/urandom of=sample1 count=1 bs=1M 2> /dev/null || fail=1
+[ "`stat -c %s sample1`" = "1048576" ] || fail=1
+
+# test 1
+dd if=sample1 of=test1 seek=0 bs=1M 2> /dev/null || fail=1
+dd if=sample0 of=test1 seek=1 bs=1M 2> /dev/null || fail=1
+dd if=sample1 of=test1 seek=2 bs=1M 2> /dev/null || fail=1
+
+# test 1-1
+dd if=test1 of=out1-1 conv=sparse bs=1M 2> /dev/null || fail=1
+dd if=sample1 of=out1-1-check bs=1M 2> /dev/null || fail=1
+dd if=sample1 of=out1-1-check seek=2 bs=1M 2> /dev/null || fail=1
+[ "`stat -c '%s %b %B' out1-1`" = "`stat -c '%s %b %B' out1-1-check`" ] ||
fail=1
+
+# test 1-2
+dd if=test1 of=out1-2 seek=1 conv=sparse bs=1M 2> /dev/null || fail=1
+dd if=sample1 of=out1-2-check seek=1 bs=1M 2> /dev/null || fail=1
+dd if=sample1 of=out1-2-check seek=3 bs=1M 2> /dev/null || fail=1
+[ "`stat -c '%s %b %B' out1-2`" = "`stat -c '%s %b %B' out1-2-check`" ] ||
fail=1
+
+# test 1-3
+dd if=test1 of=out1-3 seek=1 skip=1 conv=sparse bs=1M 2> /dev/null || fail=1
+dd if=sample1 of=out1-3-check seek=2 bs=1M 2> /dev/null || fail=1
+[ "`stat -c '%s %b %B' out1-3`" = "`stat -c '%s %b %B' out1-3-check`" ] ||
fail=1
+
+# test 2
+dd if=sample0 of=test2 seek=0 bs=1M 2> /dev/null || fail=1
+dd if=sample1 of=test2 seek=1 bs=1M 2> /dev/null || fail=1
+dd if=sample0 of=test2 seek=2 bs=1M 2> /dev/null || fail=1
+
+# test 2-1
+dd if=test2 of=out2-1 conv=sparse bs=1M 2> /dev/null || fail=1
+dd if=sample1 of=out2-1-check seek=1 bs=1M 2> /dev/null || fail=1
+[ "`stat -c '%s %b %B' out2-1`" = "`stat -c '%s %b %B' out2-1-check`" ] ||
fail=1
+
+# test 2-2
+dd if=test2 of=out2-2 seek=1 conv=sparse bs=1M 2> /dev/null || fail=1
+dd if=sample1 of=out2-2-check seek=2 bs=1M 2> /dev/null || fail=1
+[ "`stat -c '%s %b %B' out2-2`" = "`stat -c '%s %b %B' out2-2-check`" ] ||
fail=1
+
+# test 2-3
+dd if=test2 of=out2-3 seek=1 skip=1 conv=sparse bs=1M 2> /dev/null || fail=1
+dd if=sample1 of=out2-3-check seek=1 bs=1M 2> /dev/null || fail=1
+[ "`stat -c '%s %b %B' out2-3`" = "`stat -c '%s %b %B' out2-3-check`" ] ||
fail=1
+
+Exit $fail
--
1.7.0.4
--- End Message ---
--- Begin Message ---
Subject: |
Re: bug#9157: [PATCH] dd: sparse conv flag |
Date: |
Tue, 28 Feb 2012 21:49:43 +0000 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:6.0) Gecko/20110816 Thunderbird/6.0 |
On 02/28/2012 06:24 PM, Paul Eggert wrote:
> On 02/28/2012 09:01 AM, Pádraig Brady wrote:
>
>> Doing that would be "dangerous" as I said above,
>> or in other words, surprising to users to not update
>> possibly non NUL data in the output file.
>
> It's not surprising at all. It's what I want and
> expect. For example, suppose every nonzero byte of file A
> has an offset that is in a hole of file B. Then I should
> be able to overlay A and B into another file C, as follows:
>
> dd if=A of=C conv=sparse
> dd if=B of=C conv=sparse,notrunc
>
> This is akin to the "or" operation on files, and it'd be a nice
> operation to have. Even if A's contents don't fit in B's holes,
> I still might want to do the above, to allow B's non-holes to
> override A's contents. Why disable this useful functionality?
>
> Any surprise issues can be dealt with by documenting dd's
> behavior appropriately.
Fair enough. So this is the "write mask" functionality
I referred to, and which is now supported consistently
since the write(fd,"\0",1) to ftruncate() change.
>> +Try to seek rather than write @sc{nul} output blocks.
>> +This will create sparse output when extending.
>> +This option is ignored in conjunction with
>> address@hidden or @samp{oflag=append}.
>
> I still dubious about this level of handholding.
> dd is meant for low-level use, and as far as possible
> options should be orthogonal. For example, with dd,
> oflag=append does not disable seek=N -- both flags operate,
> which means that the seek is ineffective unless it
> is past the end of file. conv=sparse oflag=append
> should be similar: all it should mean is that the
> writes are sparse when they're past the end of
> the file (this latter functionality should work, but
> doesn't work with the proposed patch).
OK I'll remove the 2 restrictions, and essentially
move the comments for them from code to texinfo.
cheers,
Pádraig.
--- End Message ---