Easier printing of unknown-size quantities

We have a number of types whose sizes are architecture- or config-dependent such as pgoff_t or sector_t. The recommendation for printing them is to cast them to (unsigned long long) and print them with %Lu/%llx/... That's entirely reasonable except that it's so verbose. I was wishing that C had a more succinct way to express that, when it struct me that we can fix this without changing the compiler or language spec, viz:

index ecb8754..011b55e 100644
@@ -28,7 +28,7 @@
 #define LLONG_MIN	(-LLONG_MAX - 1)
 #define ULLONG_MAX	(~0ULL)
 #define SIZE_MAX	(~(size_t)0)
+#define ULL(x)		((unsigned long long)(x))
 
 #define STACK_MAGIC	0xdeadbeef
 

For demonstration purposes only (because I have another patch series that would conflict with this):

index 6024877..50e2596 100644
@@ -148,7 +148,7 @@ static void buffer_io_error(struct buffer_head *bh)
 {
 	char b[BDEVNAME_SIZE];
 	printk(KERN_ERR "Buffer I/O error on device %s, logical block %Lu\n",
-			bdevname(bh->b_bdev, b),
-			(unsigned long long)bh->b_blocknr);
+			bdevname(bh->b_bdev, b), ULL(bh->b_blocknr));
 }
 

/*
@@ -257,8 +256,7 @@ __find_get_block_slow(struct block_device *bdev, sector_t block)

printk("__find_get_block_slow() failed. "
"block=%llu, b_blocknr=%llu\n",
- (unsigned long long)block,
- (unsigned long long)bh->b_blocknr);
+ ULL(block), ULL(bh->b_blocknr));
printk("b_state=0x%08lx, b_size=%zu\n",
bh->b_state, bh->b_size);
printk("device %s blocksize: %d\n", bdevname(bdev, b),
@@ -1083,8 +1081,7 @@ grow_buffers(struct block_device *bdev, sector_t block, int size)
char b[BDEVNAME_SIZE];

printk(KERN_ERR "%s: requested out-of-range block %llu for "
- "device %s\n",
- __func__, (unsigned long long)block,
+ "device %s\n", __func__, ULL(block),
bdevname(bdev, b));
return -EIO;
}

Seems like a clear win to me. What do others think? Might create a bit of churn, but I find the "after" version easier to read than the former.

This is an RFC, not a PATCH, so I have deliberately mangled the patches to not apply. I'm happy to supply working patches after we've bikeshedded this one around a bit. I'm also happy to introduce it, but forbid any mass conversion patches for a year until code has had the chance to start using it.

In fact, let me help start the bikeshedding. I was trying to decide what I wanted this to print:

	unsigned int x, y;
	x = y = 0x80000000;
	printf("%llx\n", ULL(x+y));

I decided that I didn't want to magically fix the overflow, but rather expose it. After all, if the user wants the promotion, they can always write ULL(x)+y. That's why there are extra parens in the definition of ULL.

I also considered naming the macro Lu(x) so you could use it like this:

	printf("%Lu\n", Lu(x));

which is kind of cute, but it seemed clearer to me to name it the same as the integer suffixes.

Matthew Wilcox				Intel Open Source Technology Centre
"Bill, look, we understand that you're interested in selling us this
operating system, but compare it to ours.  We can't possibly take such
a retrograde step."

[]

	printk(KERN_ERR "Buffer I/O error on device %s, logical block %Lu\n",
			bdevname(bh->b_bdev, b), (u64)bh->b_blocknr);