[PATCH V2] fix readahead calculations in xfs_dir2_leaf_getdents()

[Alex Elder]

Eric Sandeen wrote:
> Christoph Hellwig wrote:
>> On Fri, Sep 25, 2009 at 02:42:26PM -0500, Eric Sandeen wrote:
>>> V2: use min() as suggested by Jeff, it's tidier.
>> 
>> I disagree with that, with the cast it looks pretty horrible.
>> At least use min_t to avoid the case, but what's wrong with:
>> 
>>> +		/* bufsize may have just been a guess; don't go negative */
>>> +		bufsize = min((bufsize - length), (size_t)0);
>> 
>> 		bufsize = bufsize - length > 0 ? bufsize - length : 0;
> 
> ok, that's fine too.
> 
> I'll pick one.
> 
>> Anyway, takes this as a
>> 
>> 
>> Reviewed-by: Christoph Hellwig <hch at lst.de>
>> 
>> for any variant.
>> 
> 
> thanks,
> -Eric

I'm going to put in this version:

		bufsize = bufsize > length ? bufsize - length : 0;

I.e.:

--- a/fs/xfs/xfs_dir2_leaf.c
+++ b/fs/xfs/xfs_dir2_leaf.c
@@ -854,6 +854,7 @@ xfs_dir2_leaf_getdents(
 			 */
 			ra_want = howmany(bufsize + mp->m_dirblksize,
 					  mp->m_sb.sb_blocksize) - 1;
+			ASSERT(ra_want >= 0);
 
 			/*
 			 * If we don't have as many as we want, and we haven't
@@ -1088,7 +1089,8 @@ xfs_dir2_leaf_getdents(
 		 */
 		ptr += length;
 		curoff += length;
-		bufsize -= length;
+		/* bufsize may have just been a guess; don't go negative */
+		bufsize = bufsize > length ? bufsize - length : 0;
 	}
 
 	/*

					-Alex