fallocate: Clarify that space can also be deallocated

The functionality is already there, with --punch-hole, but the text was for the
preallocation case only.

Signed-off-by: Rodrigo Campos <rodrigo@sdfg.com.ar>
fallocate: Hide #ifdef tricks to call fallocate in a function

Future patches will add more calls to fallocate(), so it will be useful to have
all these tricks inside a function.

The error message when fallocate is not supported is slightly changed: the file
name is not printed as a prefix because is not available in the context of the
function. Also, to only print one of the two possible errors (as happens when
using directly exit()), an else clause was added.

Signed-off-by: Rodrigo Campos <rodrigo@sdfg.com.ar>
fallocate: Add "--dig-holes" option

This option tries to detect chunk of '\0's and punch a hole, making the file
sparse in-place.

[kzak@redhat.com: - fix coding style, use xalloc.h and err.h]

Signed-off-by: Rodrigo Campos <rodrigo@sdfg.com.ar>
Signed-off-by: Karel Zak <kzak@redhat.com>
build-sys: allow per directory build targets

The new --disable-miscutils type of options are meant added for
distribution maintainers who need sometimes only to build util-linux
libraries to bootstrap fresh systems or new architectures.

References: http://www.spinics.net/lists/util-linux-ng/index.html#08695
Signed-off-by: Sami Kerola <kerolasa@iki.fi>
build-sys: add libs-only to config-gen.d

Signed-off-by: Sami Kerola <kerolasa@iki.fi>
tools: make config-gen to require build target argument

When argument is not supplied help user by telling what arguments can be
used.

Signed-off-by: Sami Kerola <kerolasa@iki.fi>
tests: check commands needed for running a test exist

Signed-off-by: Sami Kerola <kerolasa@iki.fi>