[PATCH] classes-recipe/image: Add variable to create rootfs with a exact size

[Fabio Berton <fbberton@gmail.com>]

From: Fabio Berton <fabio.berton@criticaltechworks.com>

Add the IMAGE_ROOTFS_EXACT_SIZE variable to allow the creation of a root
filesystem with an exact size as specified by the user. This bypasses
the default size calculation done by the get_rootfs_size function.

This feature is useful for creating a small ext4 filesystem with a block
size of 1k. The get_rootfs_size function uses a block size of 4k to
determine the size of IMAGE_ROOTFS, which may be larger than the value
set in IMAGE_ROOTFS_SIZE. If an ext4 rootfs with a block size of 1K is
nearly full, the .ext4 file generated by Yocto will be larger than
expected due to the way get_rootfs_size calculates the size.

By using IMAGE_ROOTFS_EXACT_SIZE, users can specify the exact size
required. Users should ensure that the size is set correctly according
to the filesystem requirements. It is not easy to predict the block size
that is used by a filesystem because it can be set by a parameter or it
can be added automatically by the tool that creates the file system.

Signed-off-by: Fabio Berton <fabio.berton@criticaltechworks.com>
---
 meta/classes-recipe/image.bbclass | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/meta/classes-recipe/image.bbclass b/meta/classes-recipe/image.bbclass
index 378d3bd0d4..419bb6cc14 100644
--- a/meta/classes-recipe/image.bbclass
+++ b/meta/classes-recipe/image.bbclass
@@ -132,7 +132,7 @@ python () {
 
 def rootfs_variables(d):
     from oe.rootfs import variable_depends
-    variables = ['IMAGE_DEVICE_TABLE','IMAGE_DEVICE_TABLES','BUILD_IMAGES_FROM_FEEDS','IMAGE_TYPES_MASKED','IMAGE_ROOTFS_ALIGNMENT','IMAGE_OVERHEAD_FACTOR','IMAGE_ROOTFS_SIZE','IMAGE_ROOTFS_EXTRA_SPACE',
+    variables = ['IMAGE_DEVICE_TABLE','IMAGE_DEVICE_TABLES','BUILD_IMAGES_FROM_FEEDS','IMAGE_TYPES_MASKED','IMAGE_ROOTFS_ALIGNMENT','IMAGE_OVERHEAD_FACTOR','IMAGE_ROOTFS_SIZE', 'IMAGE_ROOTFS_EXACT_SIZE', 'IMAGE_ROOTFS_EXTRA_SPACE',
                  'IMAGE_ROOTFS_MAXSIZE','IMAGE_NAME','IMAGE_LINK_NAME','IMAGE_MANIFEST','DEPLOY_DIR_IMAGE','IMAGE_FSTYPES','IMAGE_INSTALL_COMPLEMENTARY','IMAGE_LINGUAS', 'IMAGE_LINGUAS_COMPLEMENTARY', 'IMAGE_LOCALES_ARCHIVE',
                  'MULTILIBRE_ALLOW_REP','MULTILIB_TEMP_ROOTFS','MULTILIB_VARIANTS','MULTILIBS','ALL_MULTILIB_PACKAGE_ARCHS','MULTILIB_GLOBAL_VARIANTS','BAD_RECOMMENDATIONS','NO_RECOMMENDATIONS',
                  'PACKAGE_ARCHS','PACKAGE_CLASSES','TARGET_VENDOR','TARGET_ARCH','TARGET_OS','OVERRIDES','BBEXTENDVARIANT','FEED_DEPLOYDIR_BASE_URI','INTERCEPT_DIR','USE_DEVFS',
@@ -596,9 +596,14 @@ def get_rootfs_size(d):
     return base_size
 
 python set_image_size () {
-        rootfs_size = get_rootfs_size(d)
-        d.setVar('ROOTFS_SIZE', str(rootfs_size))
-        d.setVarFlag('ROOTFS_SIZE', 'export', '1')
+    rootfs_size = d.getVar('IMAGE_ROOTFS_EXACT_SIZE')
+    # If IMAGE_ROOTFS_EXACT_SIZE variable is not set, use the result of
+    # get_rootfs_size as ROOTFS_SIZE.
+    if not rootfs_size:
+        rootfs_size = str(get_rootfs_size(d))
+
+    d.setVar('ROOTFS_SIZE', rootfs_size)
+    d.setVarFlag('ROOTFS_SIZE', 'export', '1')
 }
 
 #
-- 
2.49.0