Xen devel - Oct 2004 - xen 2.6.8.1 sparse diff

So, I''m begining to look more closely at xen.  Trying to get it all to
compile, and work with our hardware.

After overlaying the 2.6.8.1 sparse tree, I looked at the diff of the source.
In net/core/skbuff.c, I see a function alloc_skb_from_cache.  This function
uses goto, when it''s not needed.

+struct sk_buff *alloc_skb_from_cache(kmem_cache_t *cp,
+                                    unsigned int size, int gfp_mask)
+{
+       struct sk_buff *skb;
+       u8 *data;
+
+       /* Get the HEAD */
+       skb = kmem_cache_alloc(skbuff_head_cache,
+                              gfp_mask & ~__GFP_DMA);
+       if (!skb)
+               goto out;

Replace the above 2 lines with:

if (!skb)
	return NULL;

+
+       /* Get the DATA. */
+       size = SKB_DATA_ALIGN(size);
+       data = kmem_cache_alloc(cp, gfp_mask);
+       if (!data)
+               goto nodata;

Replace the above 2 lines with:

if (!data) {
	kmem_cache_free(skbuff_head_cache, skb);
	return NULL;
}

+
+       memset(skb, 0, offsetof(struct sk_buff, truesize));
+       skb->truesize = size + sizeof(struct sk_buff);
+       atomic_set(&skb->users, 1);
+       skb->head = data;
+       skb->data = data;
+       skb->tail = data;
+       skb->end  = data + size;
+
+       atomic_set(&(skb_shinfo(skb)->dataref), 1);
+       skb_shinfo(skb)->nr_frags  = 0;
+       skb_shinfo(skb)->tso_size = 0;
+       skb_shinfo(skb)->tso_segs = 0;
+       skb_shinfo(skb)->frag_list = NULL;
+out:

Remove this line.

+       return skb;
+nodata:
+       kmem_cache_free(skbuff_head_cache, skb);
+       skb = NULL;
+       goto out;

Remove these 4 lines.

Also, why use atomic_set here?  Wouldn''t this newly allocated skb only
have
one reference?


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> So, I''m begining to look more closely at xen.  Trying to get it
all to
> compile, and work with our hardware.
> 
> After overlaying the 2.6.8.1 sparse tree, I looked at the diff of the
source.
> In net/core/skbuff.c, I see a function alloc_skb_from_cache.  This function
> uses goto, when it''s not needed.
Firstly, that function is a minimal modification of
alloc_skb(). Secondly, that style of exit/error/unusual path using
''goto'' is used throughout Linux, for good reasons:
 1. Having a common exit path per function reduces bugs as only need
    to write epilogue code once. Hence the ''out'' label.
 2. Older gcc versions need help in outlining rarely-executed basic
    blocks. Hence the ''nodata'' label.

 -- Keir


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Use IT products in your business? Tell us what you think of them. Give us
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Xen-devel@lists.sourceforge.net
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