stat: revert %X-%Y-%Z change; use e.g., %:X to print fractional seconds

This reverts part of the recent commit 9069af45,
"stat: print timestamps to full resolution", which made %X, %Y, %Z
print floating point numbers.  We prefer to retain portability of
%X, %Y and %Z uses, while still providing access to full-resolution
time stamps via modified format strings.  Also make the new
%W consistent.
* src/stat.c: Include "xstrtol.h".
(print_it): Accept a new %...:[XYZ] format directive,
e.g., %:X, to print the nanoseconds portion of the corresponding time.
For example, %3.3:Y prints the zero-padded, truncated, milliseconds
part of the time of last modification.
(print_it): Update print_func signature to match.
(neg_to_zero): New helper function.
(epoch_time): Remove function; replace with...
(epoch_sec): New function; use timetostr.
(out_ns): New function.  Use "09" only when no other modifier
is specified.
(print_statfs): Change type of "m" to unsigned int,
now that it must accommodate values larger than 255.
(print_stat): Likewise.
Map :X to a code of 'X' + 256.  Likewise for Y, Z and W.
(usage): Update.
* tests/touch/60-seconds: Use %Y.%:Y in place of %Y.
* tests/misc/stat-nanoseconds: New file.
* tests/Makefile.am (TESTS): Add it.
* NEWS (Changes in behavior): Mention this.
With improvements by Pádraig Brady.
Thanks to Andreas Schwab for raising the issue.

1 files changed, 26 insertions, 1 deletions

diff --git a/doc/coreutils.texi b/doc/coreutils.texi
index 0b5a3d341..be5999ffe 100644
--- a/doc/coreutils.texi
+++ b/doc/coreutils.texi
@@ -10706,15 +10706,40 @@ The valid @var{format} directives for files with @option{--format} and
 @item %u - User ID of owner
 @item %U - User name of owner
 @item %w - Time of file birth, or @samp{-} if unknown
-@item %W - Time of file birth as seconds since Epoch, or @samp{-}
+@item %W - Time of file birth as seconds since Epoch, or @samp{0}
+@item %:W - Time of file birth: nanoseconds remainder, or @samp{0}
 @item %x - Time of last access
 @item %X - Time of last access as seconds since Epoch
+@item %:X - Time of last access: nanoseconds remainder
 @item %y - Time of last modification
 @item %Y - Time of last modification as seconds since Epoch
+@item %:Y - Time of last modification: nanoseconds remainder
 @item %z - Time of last change
 @item %Z - Time of last change as seconds since Epoch
+@item %:Z - Time of last change: nanoseconds remainder
 @end itemize
 
+Note that each of @samp{%:W}, @samp{%:X}, @samp{%:Y} and @samp{%:Z}
+prints its zero-padded number of nanoseconds on a field of width 9.
+However, if you specify anything between the @samp{%} and @samp{:},
+e.g., @samp{%10:X}, your modifier replaces the default of @samp{09}.
+
+Here are some examples:
+
+@example
+zero pad:
+  $ stat -c '[%015:Y]' /usr
+  [000000031367045]
+space align:
+  $ stat -c '[%15:Y]' /usr
+  [       31367045]
+  $ stat -c '[%-15:Y]' /usr
+  [31367045       ]
+truncate:
+  $ stat -c '[%.3:Y]' /usr
+  [031]
+@end example
+
 The mount point printed by @samp{%m} is similar to that output
 by @command{df}, except that:
 @itemize @bullet