Re: [PATCH] bitmap parsing/printing routines, version 4

[Matthew Dobson <colpatch@us.ibm.com>]

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Joe Korty wrote:
>>>However, IMHO you added too many comments.  Unlike Andrew, I do believe
>>>one can have too many comments.  Comments become 'too many' when they
>>>dilute to the point that the code can no longer be clearly read.
>>>
>>>If you reduce the comments to just those that say something not easily
>>>deduced from the code, then they would be acceptable to me, and would
>>>make a useful addition IMO.  That would be all but three, or perhaps four,
>>>of them.
>>>
>>>Andrew, if you do like the fully commented version, then please remove
>>>my name from the comment in the patch.  The dilute style of coding is
>>>not one I wish to have my name associated with.
>>>
>>>Thanks,
>>>Joe
>>
>>I'm sorry you feel that way, Joe.  I had no intention of "diluting" your 
>>code, and I certainly don't want you to remove your name from good code 
>>you spent significant time & effort on.  I'm just about to go to sleep, 
>>so I made this patch pretty quickly.  I think the 4 comments I kept are 
>>the most useful and non-obvious.  Let me know if this looks acceptable 
>>to you.  As I said, I have no desire to have you pull your name from the 
>>code, especially since I feel it is good code!
>>
>>Andrew, once Joe and I work out an acceptable patch, we'll make sure you 
>>get a copy.
> 
> 
> Much better, Matthew.  I can live with this latest patch:)
> Thanks,
> Joe

Great!  Ok Andrew, I've rediffed this patch against -mm5, and the 
attatched patch should apply cleanly.

Joe & Paul, kudos on the code.  Looks great!

-Matt


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diff -Nurp --exclude-from=/home/mcd/.dontdiff linux-2.6.1-mm5/lib/bitmap.c linux-2.6.1-bitmap_readability/lib/bitmap.c
--- linux-2.6.1-mm5/lib/bitmap.c	Tue Jan 20 08:56:40 2004
+++ linux-2.6.1-bitmap_readability/lib/bitmap.c	Tue Jan 20 09:00:28 2004
@@ -210,13 +210,13 @@ EXPORT_SYMBOL(bitmap_snprintf);
  * bits of the resultant bitmask.  No chunk may specify a value larger
  * than 32 bits (-EOVERFLOW), and if a chunk specifies a smaller value
  * then leading 0-bits are prepended.  -EINVAL is returned for illegal
- * characters and for grouping errors such as "1,,5", ,44", "," and "".
+ * characters and for grouping errors such as "1,,5", ",44", "," and "".
  * Leading and trailing whitespace accepted, but not embedded whitespace.
  */
 int bitmap_parse(const char __user *ubuf, unsigned int ubuflen,
         unsigned long *maskp, int nmaskbits)
 {
-	int i, c, oc, ndigits, totaldigits, nchunks, nbits;
+	int i, c, old_c, totaldigits, ndigits, nchunks, nbits;
 	u32 chunk;
 
 	bitmap_clear(maskp, nmaskbits);
@@ -224,21 +224,39 @@ int bitmap_parse(const char __user *ubuf
 	nchunks = nbits = totaldigits = c = 0;
 	do {
 		chunk = ndigits = 0;
+
+		/* Get the next chunk of the bitmap */
 		while (ubuflen) {
-			oc = c;
+			old_c = c;
 			if (get_user(c, ubuf++))
 				return -EFAULT;
 			ubuflen--;
 			if (isspace(c))
 				continue;
-			if (totaldigits && c && isspace(oc))
+
+			/*
+			 * If the last character was a space and the current 
+			 * character isn't '\0', we've got embedded whitespace.
+			 * This is a no-no, so throw an error.
+			 */
+			if (totaldigits && c && isspace(old_c))
 				return -EINVAL;
-			if (!c || c == ',')
+
+			/* A '\0' or a ',' signal the end of the chunk */
+			if (c == '\0' || c == ',')
 				break;
+
 			if (!isxdigit(c))
 				return -EINVAL;
+
+			/*
+			 * Make sure there are at least 4 free bits in 'chunk'.
+			 * If not, this hexdigit will overflow 'chunk', so 
+			 * throw an error.
+			 */
 			if (chunk & ~((1UL << (CHUNKSZ - 4)) - 1))
 				return -EOVERFLOW;
+
 			chunk = (chunk << 4) | unhex(c);
 			ndigits++; totaldigits++;
 		}
@@ -246,6 +264,7 @@ int bitmap_parse(const char __user *ubuf
 			return -EINVAL;
 		if (nchunks == 0 && chunk == 0)
 			continue;
+
 		bitmap_shift_right(maskp, maskp, CHUNKSZ, nmaskbits);
 		for (i = 0; i < CHUNKSZ; i++)
 			if (chunk & (1 << i))
@@ -256,8 +275,6 @@ int bitmap_parse(const char __user *ubuf
 			return -EOVERFLOW;
 	} while (ubuflen && c == ',');
 
-	if (totaldigits == 0)
-		return -EINVAL;
 	return 0;
 }
 EXPORT_SYMBOL(bitmap_parse);