lib: make the loop device size can be increased

index f927fc6..9c412be 100644
@@ -1323,12 +1323,16 @@ Following functions similar to the LTP C interface are available.
 * tst_rmdir()
 * tst_fs_has_free()
 * tst_mkfs()
-* tst_acquire_device()
 * tst_release_device()
 
-There is one more function called 'tst_check_cmds()' that gets unspecified
-number of parameters and asserts that each parameter is a name of an
-executable in '$PATH' and exits the test with 'TCONF' on first missing.
+One more function called 'tst_check_cmds()' that gets unspecified number
+of parameters and asserts that each parameter is a name of an executable
+in '$PATH' and exits the test with 'TCONF' on first missing.
+
+Another one is 'tst_acquire_device()' that looks for LTP_DEV env variable
+first (which may be passed by the test driver or by a user) and returns while
+it's value greater than 150MB. It also does clear first sectors of $LTP_DEV
+and makes the block device size can be increased according to real need.
 
 tst_sleep
 +++++++++

index c5b643f..1b83738 100644
@@ -12,3 +12,4 @@ test11
 test12
 test13
 tst_safe_fileops
+tst_device

index a1fa2d9..76b7062 100644
@@ -283,11 +283,15 @@ EXPECT_FAIL()
 
 tst_acquire_device()
 {
+	local acq_dev_size=${1:-150}
+
 	if [ -z ${TST_TMPDIR} ]; then
 		tst_brkm "Use 'tst_tmpdir' before 'tst_acquire_device'"
 	fi
 
-	if [ -n "${LTP_DEV}" ]; then
+	ltp_dev_size=$((`blockdev --getsize64 $LTP_DEV`/1024/1024))
+
+	if [ -n "${LTP_DEV}" ] && [ ${acq_dev_size} -le ${ltp_dev_size} ]; then
 		tst_resm TINFO "Using test device LTP_DEV='${LTP_DEV}'"
 		if [ ! -b ${LTP_DEV} ]; then
 			tst_brkm TBROK "${LTP_DEV} is not a block device"

@@ -300,7 +304,7 @@ tst_acquire_device()
 		return
 	fi
 
-	ROD_SILENT dd if=/dev/zero of=test_dev.img bs=1024 count=153600
+	ROD_SILENT dd if=/dev/zero of=test_dev.img bs=1024 count=$((1024*$acq_dev_size))
 
 	TST_DEVICE=$(losetup -f)
 	if [ $? -ne 0 ]; then

index a27f24f..384ff09 100644
@@ -904,6 +904,10 @@ If '.needs_device' flag in the 'struct tst_test' is set the the 'tst_device'
 structure is initialized with a path to a test device and default filesystem
 to be used.
 
+You can also request minimal device size in megabytes by setting
+'.device_min_size' in the 'struct tst_test' structure. The device is
+guaranteed to have at least the requested size then.
+
 [source,c]
 -------------------------------------------------------------------------------
 #include "tst_test.h"

@@ -919,8 +923,10 @@ int tst_umount(const char *path);
 -------------------------------------------------------------------------------
 
 In case that 'LTP_DEV' is passed to the test in an environment, the library
-checks that the file exists and that it's a block device. Otherwise a
-temporary file is created and attached to a free loop device.
+checks that the file exists and that it's a block device, if
+'.device_min_size' is set the device size is checked as well. If 'LTP_DEV'
+wasn't set or if size requirements were not met a temporary file is created
+and attached to a free loop device.
 
 If there is no usable device and loop device couldn't be initialized the test
 exits with 'TCONF'.

@@ -1330,14 +1336,24 @@ Following functions similar to the LTP C interface are available.
 * tst_mkfs()
 * tst_release_device()
 
-One more function called 'tst_check_cmds()' that gets unspecified number
-of parameters and asserts that each parameter is a name of an executable
-in '$PATH' and exits the test with 'TCONF' on first missing.
+tst_check_cmds
+++++++++++++++
+
+The 'tst_check_cmds()' function that gets unspecified number of parameters and
+asserts that each parameter is a name of an executable in '$PATH' and exits
+the test with 'TCONF' on first missing.
+
+tst_acquire_device
+++++++++++++++++++
+
+The 'tst_acquire_device()' can be used to obtain a block device for testing,
+the function takes optional parameter which can be used to request device
+minimal size in megabytes.
 
-Another one is 'tst_acquire_device()' that looks for LTP_DEV env variable
-first (which may be passed by the test driver or by a user) and returns while
-it's value greater than 150MB. It also does clear first sectors of $LTP_DEV
-and makes the block device size can be increased according to real need.
+The function returns device passed in 'LTP_DEV' environment variable if it's
+set, points to a block device, and if size requirements are met. If 'LTP_DEV'
+is not set or found suitable a temporary file is created and attached to a
+free loop device.
 
 tst_sleep
 +++++++++