[PATCH v2 2/2] runqemu: resize rootfs image to power of 2 for SD or pflash

[Jon Mason <jon.mason@arm.com>]

QEMU requires that SD and pflash images are sized to be a power of 2
(e.g., 32M, 64M, etc).  So, if the image being used is not a power of 2
and it's being used for SD or pflash, increase it to the next power of 2
size via the truncate command.

This might not be an actual spec requirement, and is being investigated
in https://gitlab.com/qemu-project/qemu/-/issues/1754

Signed-off-by: Jon Mason <jon.mason@arm.com>
---
 scripts/runqemu | 25 ++++++++++++++++++++++---
 1 file changed, 22 insertions(+), 3 deletions(-)

diff --git a/scripts/runqemu b/scripts/runqemu
index a8144aa68c3d..21d75ad8a319 100755
--- a/scripts/runqemu
+++ b/scripts/runqemu
@@ -421,8 +421,27 @@ class BaseConfig(object):
         else:
             raise RunQemuError("Unknown path arg %s" % p)
 
-    def uncompress_rootfs(self):
-        """Decompress ZST rootfs image if needed"""
+    def rootfs_fixups(self):
+
+        """Decompress and/or resize the rootfs image, if needed"""
+        qb_rootfs_opt = self.get('QB_ROOTFS_OPT')
+
+        # Check if sdcard size is a power of 2, as that is currently a requirement for qemu
+        # See https://gitlab.com/qemu-project/qemu/-/issues/1754
+        rootfs_size = os.path.getsize(self.rootfs)
+        rootfs_size_pwr2 = 1 << (rootfs_size - 1).bit_length()
+        if ("if=sd" in qb_rootfs_opt or "if=pflash" in qb_rootfs_opt) and rootfs_size != rootfs_size_pwr2:
+            logger.info("Using sd-card or pflash and is not power of 2. File size %d, power of 2 size %d" %(rootfs_size, rootfs_size_pwr2))
+            logger.info("Attempting to use truncate to correct this.")
+
+            # Ensure the 'truncate' tool is installed before attempting to make a power of 2.
+            if not shutil.which('truncate'):
+                raise RunQemuError(f"'truncate' is required to make {self.rootfs} a power of 2 in size but was not found in PATH")
+            try:
+                subprocess.check_call(['truncate', '-s', str(rootfs_size_pwr2), self.rootfs])
+            except subprocess.CalledProcessError as e:
+                raise RunQemuError(f"Failed to make {self.rootfs} power of 2 in size: {e}")
+
         if not self.rootfs or not self.fstype.endswith('.zst'):
             return
         
@@ -1808,7 +1827,7 @@ def main():
         config.check_args()
         config.read_qemuboot()
         config.check_and_set()
-        config.uncompress_rootfs()
+        config.rootfs_fixups()
         # Check whether the combos is valid or not
         config.validate_combos()
         config.print_config()
-- 
2.50.1 (Apple Git-155)