Messages in this thread | | | From | "Sirotkin, Alexander" <> | Date | Tue, 13 Jan 2004 11:25:56 +0200 | Subject | adding preallocated data to skb |
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A number of other OSs I worked with (namely windows and VxWorks) has this sometimes very convinient feature - you can allocate dma buffers and then, after DMA receive is finished, you can allocate an empty mblock (which is a VxWorks skb) and just add preallocated data to this empty mblock.
This is extremely convinient, especially for fragmented packets.
I could not find anything similar in Linux, however it seems to me that it should be quite streightforward to implement.
All that needs to be done is to break alloc_skb() into two functions, similar to the following : (it's just a C pseudo code, it does not compile - only demonstrates an idea)
struct sk_buff *alloc_empty_skb() { struct sk_buff *skb;
if (in_interrupt() && (gfp_mask & __GFP_WAIT)) { static int count = 0; if (++count < 5) { printk(KERN_ERR "alloc_skb called nonatomically " "from interrupt %p\n", NET_CALLER(size)); BUG(); } gfp_mask &= ~__GFP_WAIT; }
/* Get the HEAD */ skb = skb_head_from_pool(); if (skb == NULL) { skb = kmem_cache_alloc(skbuff_head_cache, gfp_mask & ~__GFP_DMA); if (skb == NULL) goto nohead; }
atomic_set(&skb->users, 1);
return skb;
nohead: return NULL; }
int skb_add_data(u8 * data, struct sk_buff * skb, int size) { if (data == NULL) goto nodata;
/* XXX: does not include slab overhead */ skb->truesize = size + sizeof(struct sk_buff);
/* Load the data pointers. */ skb->head = data; skb->data = data; skb->tail = data; skb->end = data + size;
/* Set up other state */ skb->len = 0; skb->cloned = 0; skb->data_len = 0;
atomic_set(&(skb_shinfo(skb)->dataref), 1); skb_shinfo(skb)->nr_frags = 0; skb_shinfo(skb)->frag_list = NULL; return 0; }
Any ideas why it should/should not work ? Anybody ever implemented anything similar ?
-- Alexander Sirotkin SW Engineer
Texas Instruments Broadband Communications Israel (BCIL) Tel: +972-9-9706587 ________________________________________________________________________ "Those who do not understand Unix are condemned to reinvent it, poorly." -- Henry Spencer
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