Ensure superblock always fits SIMPLEFS_BLOCK_SIZE

[HotMercury]

This commit ensures that the padding size always matches the block size defined by SIMPLEFS_BLOCK_SIZE.

[jserv]

In the commit message, instead of stating that "This commit ensures...," you should explain the issues or limitations present in the current implementation, such as poor cache locality. Additionally, if the proposed changes aim to enhance performance and/or improve the memory layout, utilize the term "improve" in the git commit message to accurately reflect the intended improvements.

[jserv]

_Static_assert is not a macro. It is a keyword in C11.

[jserv]

Consider the following changes:

--- a/mkfs.c
+++ b/mkfs.c
@@ -17,6 +17,8 @@ struct superblock {
     };
 };

+_Static_assert(sizeof(struct superblock) == SIMPLEFS_BLOCK_SIZE);
+
 /**
  * DIV_ROUND_UP - round up a division
  * @n: dividend
@@ -239,7 +241,6 @@ static int write_data_blocks(int fd, struct superblock *sb)

 int main(int argc, char **argv)
 {
-    _Static_assert(sizeof(struct superblock) == SIMPLEFS_BLOCK_SIZE);
     if (argc != 2) {
         fprintf(stderr, "Usage: %s disk\n", argv[0]);
         return EXIT_FAILURE;

In git commit message, you should explain why union does matter.

[jserv]

Thank @HotMercury for contributing!