Messages in this thread Patches in this message | | | Date | Thu, 9 Jan 2014 06:42:10 -0700 | From | Matthew Wilcox <> | Subject | [RFC] Easier printing of unknown-size quantities |
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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:
diff --git a/include/linux/kernel.h b/include/linux/kernel.h index ecb8754..011b55e 100644 --- a/include/linux/kernel.h +++ b/include/linux/kernel.h @@ -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): diff --git a/fs/buffer.c b/fs/buffer.c index 6024877..50e2596 100644 --- a/fs/buffer.c +++ b/fs/buffer.c @@ -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."
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