shred: provide --remove methods to avoid excessive syncing

A sync operation is very often expensive.  For illustration
I timed the following python script which indicated that
each ext4 dir sync was taking about 2ms and 12ms, on an
SSD and traditional disk respectively.

  import os
  d=os.open(".", os.O_DIRECTORY|os.O_RDONLY)
  for i in range(1000):
     os.fdatasync(d)

So syncing for each character for each file can result
in significant delays.  Often this overhead is redundant,
as only the data is sensitive and not the file name.
Even if the names are sensitive, your file system may
employ synchronous metadata updates, which also makes
explicit syncing redundant.

* tests/misc/shred-remove.sh: Ensure all the new parameters
actually unlink the file.
* doc/coreutils.texi (shred invocation): Describe the new
parameters to the --remove option.
* src/shred.c (Usage): Likewise.
(main): Parse the new options.
(wipename): Inspect the new enum to see which of
the now optional tasks to perform.
* NEWS: Mention the new feature.
* THANKS.in: Add reporter Joseph D. Wagner

1 files changed, 3 insertions, 0 deletions

diff --git a/NEWS b/NEWS
index 5791a2701..f9f3a9e8d 100644
--- a/NEWS
+++ b/NEWS
@@ -76,6 +76,9 @@ GNU coreutils NEWS                                    -*- outline -*-
   csplit accepts a new option: --suppressed-matched, to elide the lines
   used to identify the split points.
 
+  shred accepts new parameters to the --remove option to give greater
+  control over that operation, which can greatly reduce sync overhead.
+
   shuf accepts a new option: --repetitions (-r), to allow repetitions
   of input items in the permuted output.