Set ESP output minimum size based on sector size

Based on the sector size, a minimum size is required for FAT32 to
be bootable by OVMF. Instead of wasting space by always using 512MB,
let's set the minimum size based on the given sector size.

mkosi/__init__.py

@@ -2107,9 +2107,17 @@ def make_esp(state: MkosiState, uki: Path) -> list[Partition]:
     definitions = state.workspace / "esp-definitions"
     definitions.mkdir(exist_ok=True)
 
-    # Use a minimum of 512MB because otherwise the generated FAT filesystem will have too few clusters to be considered
-    # a FAT32 filesystem by OVMF which will refuse to boot from it. Always reserve 10MB for filesystem metadata.
-    size = max(uki.stat().st_size, 502 * 1024**2) + 10 * 1024**2
+    # Use a minimum of 36MB or 260MB depending on sector size because otherwise the generated FAT filesystem will have
+    # too few clusters to be considered a FAT32 filesystem by OVMF which will refuse to boot from it.
+    # See https://superuser.com/questions/1702331/what-is-the-minimum-size-of-a-4k-native-partition-when-formatted-with-fat32/1717643#1717643
+    if state.config.sector_size == 512:
+        m = 36
+    # TODO: Figure out minimum size for 2K sector size
+    else:
+        m = 260
+
+    # Always reserve 10MB for filesystem metadata.
+    size = max(uki.stat().st_size, (m - 10) * 1024**2) + 10 * 1024**2
 
     # TODO: Remove the extra 4096 for the max size once https://github.com/systemd/systemd/pull/29954 is in a stable
     # release.