bug#45648: closed (`dd` seek/skip which way is up?)

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Your message dated Tue, 22 Feb 2022 09:12:42 -0800
with message-id <236820c4-1e7d-08f9-32e2-481f97af5bde@cs.ucla.edu>
and subject line Re: bug#45648: `dd` seek/skip which way is up?
has caused the debbugs.gnu.org bug report #45648,
regarding `dd` seek/skip which way is up?
to be marked as done.

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45648: http://debbugs.gnu.org/cgi/bugreport.cgi?bug=45648
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--- Begin Message --- Subject: `dd` seek/skip which way is up? Date: Sun, 3 Jan 2021 19:03:17 -0800

Hello --

I constantly confuse 'seek=N' and 'skip=N'.  The two words have no natural affinity to one I/O direction or the other.

I previously encountered a `dd` implementation which also accepted 'oseek=N' and 'iseek=N', which I found far more natural and easy to remember.

Here is a small patch implementing the same for coreutils `dd`.  Patch is against just-gotten git tree; `dd --version` reports 'dd (coreutils) 8.32.101-ebf2c-dirty'.  (I probably got the .texi formatting wrong; please repair as needed.)

While in the area, I slightly improved some of the help (and therefore man page).

>Bela<

========================================================================

diff --git a/doc/coreutils.texi b/doc/coreutils.texi

index e9dd21c4e..417857c5e 100644

--- a/doc/coreutils.texi

+++ b/doc/coreutils.texi

@@ -9100,6 +9100,15 @@ Skip @var{n} @samp{obs}-byte blocks in the output file before copying.

 if @samp{oflag=seek_bytes} is specified, @var{n} is interpreted

 as a byte count rather than a block count.

 

+@item oseek

+@item iseek

+@opindex oseek

+@opindex iseek

+As the distinction between @samp{seek} and @samp{skip}

+is easily confused, @samp{oseek} is accepted as an alias

+for @samp{seek}; @samp{iseek} for @samp{skip}.

+Do not use these in scripts, as this reduces compatibility.

+

 @item count=@var{n}

 @opindex count

 Copy @var{n} @samp{ibs}-byte blocks from the input file, instead

@@ -9457,6 +9466,15 @@ rather than a block count, which allows specifying

 an offset that is not a multiple of the I/O block size.

 This flag can be used only with @code{oflag}.

 

+@item oseek_bytes

+@item iseek_bytes

+@opindex oseek_bytes

+@opindex iseek_bytes

+As the distinction between @samp{seek_bytes} and @samp{skip_bytes}

+is easily confused, @samp{oseek_bytes} is accepted as an alias

+for @samp{seek_bytes}; @samp{iseek_bytes} for @samp{skip_bytes}.

+Do not use these in scripts, as this reduces compatibility.

+

 @end table

 

 These flags are not supported on all systems, and @samp{dd} rejects

diff --git a/src/dd.c b/src/dd.c

index 9152a2550..a187522c2 100644

--- a/src/dd.c

+++ b/src/dd.c

@@ -381,7 +381,9 @@ static struct symbol_value const flags[] =

   {"fullblock",   O_FULLBLOCK}, /* Accumulate full blocks from input.  */

   {"count_bytes", O_COUNT_BYTES},

   {"skip_bytes",  O_SKIP_BYTES},

+  {"iseek_bytes", O_SKIP_BYTES},

   {"seek_bytes",  O_SEEK_BYTES},

+  {"oseek_bytes", O_SEEK_BYTES},

   {"", 0}

 };

 

@@ -571,7 +573,7 @@ Copy a file, converting and formatting according to the operands.\n\

                   overrides ibs and obs\n\

   cbs=BYTES       convert BYTES bytes at a time\n\

   conv=CONVS      convert the file as per the comma separated symbol list\n\

-  count=N         copy only N input blocks\n\

+  count=N         copy only N input blocks (bytes if iflag=count_bytes)\n\

   ibs=BYTES       read up to BYTES bytes at a time (default: 512)\n\

 "), stdout);

       fputs (_("\

@@ -580,8 +582,8 @@ Copy a file, converting and formatting according to the operands.\n\

   obs=BYTES       write BYTES bytes at a time (default: 512)\n\

   of=FILE         write to FILE instead of stdout\n\

   oflag=FLAGS     write as per the comma separated symbol list\n\

-  seek=N          skip N obs-sized blocks at start of output\n\

-  skip=N          skip N ibs-sized blocks at start of input\n\

+  seek=N (or oseek=N)  skip N obs-sized blocks at start of output (bytes if oflag=seek_bytes)\n\

+  skip=N (or iseek=N)  skip N ibs-sized blocks at start of input (bytes if iflag=skip_bytes)\n\

   status=LEVEL    The LEVEL of information to print to stderr;\n\

                   'none' suppresses everything but error messages,\n\

                   'noxfer' suppresses the final transfer statistics,\n\

@@ -660,10 +662,10 @@ Each FLAG symbol may be:\n\

         fputs (_("  count_bytes  treat 'count=N' as a byte count (iflag only)\n\

 "), stdout);

       if (O_SKIP_BYTES)

-        fputs (_("  skip_bytes  treat 'skip=N' as a byte count (iflag only)\n\

+        fputs (_("  skip_bytes (or iseek_bytes)  treat 'skip=N' as a byte count (iflag only)\n\

 "), stdout);

       if (O_SEEK_BYTES)

-        fputs (_("  seek_bytes  treat 'seek=N' as a byte count (oflag only)\n\

+        fputs (_("  seek_bytes (or oseek_bytes)  treat 'seek=N' as a byte count (oflag only)\n\

 "), stdout);

 

       {

@@ -1554,9 +1556,11 @@ scanargs (int argc, char *const *argv)

               n_max = SIZE_MAX;

               conversion_blocksize = n;

             }

-          else if (operand_is (name, "skip"))

+          else if (operand_is (name, "skip") ||

+                    operand_is (name, "iseek"))

             skip = n;

-          else if (operand_is (name, "seek"))

+          else if (operand_is (name, "seek") ||

+                   operand_is (name, "oseek"))

             seek = n;

           else if (operand_is (name, "count"))

             count = n;

--- End Message ---

--- Begin Message --- Subject: Re: bug#45648: `dd` seek/skip which way is up? Date: Tue, 22 Feb 2022 09:12:42 -0800 User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.5.0

On 1/4/21 20:08, Paul Eggert wrote:

On 1/4/21 7:44 PM, Bela Lubkin wrote:

TLDR: *huge* existing presence of 'iseek' and 'oseek'; most OSes document
them as pure synonyms for 'skip' and 'seek'.

Thanks for doing all that research. It's compelling, and I think your patch (or something like it) should go in. I'll wait for a bit to hear other opinions.

After thinking about the patch a bit more, let's omit the part about adding new conversions iseek_bytes etc., as I think there's a better way to address that issue. I proposed something in <https://bugs.gnu.org/54112>.

So instead of your patch, I installed the attached patches. The first one adds the iseek and oseek operands that you suggested; the second one clarifies dd documentation, as I found several things were confusing when rereading it carefully. Something like these patches should appear in the next coreutils release.

0001-dd-support-iseek-and-oseek.patch
Description: Text Data

0002-dd-improve-doc-relative-to-POSIX.patch
Description: Text Data

--- End Message ---