fallocate: (man) add hint about off/len limitations

Signed-off-by: Karel Zak <kzak@redhat.com>

diff --git a/sys-utils/fallocate.1 b/sys-utils/fallocate.1
index 9e214c73624030755c1adb3eb6fe1c76ec6db0d4..cabc41fdb1a9bd5ca3388369a3a275de0ab0c522 100644 (file)
--- a/sys-utils/fallocate.1
+++ b/sys-utils/fallocate.1
@@ -33,6 +33,17 @@ preallocation is done quickly by allocating blocks and marking them as
 uninitialized, requiring no IO to the data blocks.
 This is much faster than creating a file by filling it with zeroes.
 .PP
+.PP
+Note that a filesystem may place limitations on the granularity of some
+fallocate operations.  Typically,
+.I offset
+and
+.I lenght
+must be a multiple of the
+filesystem logical block size, which varies according to the filesystem type
+and configuration.  If a filesystem has such a requirement, the operation will
+fail with the error EINVAL (Invalid argument) if this requirement is violated.
+.PP
 The exit status returned by
 .B fallocate
 is 0 on success and 1 on failure.