genfile: improve sparse mode

* tests/genfile.c (generate_sparse_file): Handle '-' argument
(read from stdin);
If content strings starts with '=', treat it as fragment size and
use default pattern to fill it.
* doc/genfile.texi: Document changes to genfile.

1 files changed, 22 insertions, 11 deletions

diff --git a/doc/genfile.texi b/doc/genfile.texi
index e0f4e35..bd2e505 100644
--- a/doc/genfile.texi
+++ b/doc/genfile.texi
@@ -124,9 +124,8 @@ the rest of the command line specifies a so-called @dfn{file map}.
 descriptors}. Each descriptor is composed of two values: a number,
 specifying fragment offset from the end of the previous fragment or,
 for the very first fragment, from the beginning of the file, and
-@dfn{contents string}, i.e., a string of characters, specifying the
-pattern to fill the fragment with. File offset can be suffixed with
-the following quantifiers:
+@dfn{contents string}, that specifies the pattern to fill the fragment
+with. File offset can be suffixed with the following quantifiers:
 
 @table @samp
 @item k
@@ -140,17 +139,29 @@ The number is expressed in megabytes.
 The number is expressed in gigabytes.
 @end table
 
-    For each letter in contents string @command{genfile} will generate
-a @dfn{block} of data, filled with this letter and will write it to
-the fragment. The size of block is given by @option{--block-size}
-option. It defaults to 512. Thus, if the string consists of @var{n}
-characters, the resulting file fragment will contain
-@code{@var{n}*@var{block-size}} of data.
-
-    Last fragment descriptor can have only file offset part. In this
+    Contents string can be either a fragment size or a pattern.
+Fragment size is a decimal number, prefixed with an equals sign.  It
+can be suffixed with a quantifier, as discussed above.  If fragment
+size is given, the fragment of that size will be filled with the
+currently selected pattern (@pxref{Generate Mode, --pattern}) and
+written to the file.  
+
+    A pattern is a string of arbitrary ASCII characters.  For each
+of them, @command{genfile} will generate a @dfn{block} of data,
+filled with that character and will write it to the fragment. The size
+of block is given by @option{--block-size} option. It defaults to 512.
+Thus, if pattern consists of @var{n} characters, the resulting file
+fragment will contain @code{@var{n}*@var{block-size}} bytes of data.
+
+    The last fragment descriptor can have only file offset part. In this
 case @command{genfile} will create a hole at the end of the file up to
 the given offset.
 
+    A dash appearing as a fragment descriptor instructs
+@command{genfile} to read file map from the standard input.  Each line
+of input should consist of fragment offset and contents string,
+separated by any amount of whitespace.
+
     For example, consider the following invocation:
 
 @smallexample