man page: mention SEEK_HOLE

Mention that we fall-back to SEEK_HOLE when FIEMAP is not supported.

Change-Id: I3aec79f214982e6f4aec0f9900f26231a26c665f
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@intel.com>

diff --git a/docs/man1/bmaptool.1 b/docs/man1/bmaptool.1
index dffcc0824490ac2051fcad06a1c826d7b3d90b88..a1c6f0ee49b8167037653af9f051235899efb45c 100644 (file)
--- a/docs/man1/bmaptool.1
+++ b/docs/man1/bmaptool.1
@@ -222,8 +222,10 @@ from "imag.bmap.asc".
 
 .PP
 Generate bmap for a regular file IMAGE. Internally, this subcommand uses the
-Linux "FIEMAP" ioctl to find out which IMAGE blocks are mapped. By default, the
-resulting bmap file is printed to stdout, unless the "--output" option is used.
+Linux "FIEMAP" ioctl to find out which IMAGE blocks are mapped. However, if
+"FIEMAP" is not supported, the "SEEK_HOLE" feature of the "lseek" system call
+is used instead. By default, the resulting bmap file is printed to stdout,
+unless the "--output" option is used.
 
 .PP
 The IMAGE file is always synchronized before the block map is generated. And it