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Date: Wed, 18 Jul 2007 23:51:03 -0700 (PDT) From: vinay ravuri <vinaynyc@...oo.com> To: Stephen Hemminger <shemminger@...ux-foundation.org> Cc: netdev@...r.kernel.org Subject: Re: Socket Buffers and Memory Managment How about the following approach: I allocate an skb of 0 bytes and replace data element of skb struct (i.e. skb.data = addr_given_by_hw) when the h/w interrupts me with a packet. I register for a destructor for this skb and when the kernel is ready to free the skb, I make sure that my free is invoked - Ofcourse this is assuming that their is a facility in linux socket buffers to be able to do destructors. Is this approach a viable, if so, are any gottcha's? -Vinay --- Stephen Hemminger <shemminger@...ux-foundation.org> wrote: > On Tue, 17 Jul 2007 10:20:58 -0700 (PDT) > vinay ravuri <vinaynyc@...oo.com> wrote: > > > Hi, > > > > I am fairly new to linux socket buffers and have > the > > following questions! > > > > I am working with a custom ethernet MAC that does > not > > allow me to specify a particular memory location > for > > the h/w to DMA the packet into (Rx side). > Instead, it > > has a pool of fixed size buffers with some h/w > > specific headers around each buffer that are > managed > > by h/w and will pick a free buffer and DMA the > packet. > > Sounds like sucky hardware... > You need to copy to a newly allocated skb, see > 8139too.c > > > It appears dev_alloc_skb() actually allocates the > > physical memory and doesn't allow the user to > specify > > the skb.data to something specific to what I want > > which is a problem for me. First is my assumption > > correct that I am cannot pick an arbitrary > skb.data > > location in struct sk_buff? I want to avoid > copying > > the dma'ed data into a new socket buffer as it is > > expense. Is there any ways around this problem? > > You could play tricks with skb frags but it would be > fragile > and not worth the trouble. The problem is that the > receive > skb can stay in the system for a really long time > (until the application > reads the data) so your fixed size buffer pool in > hardware > would get exhausted. > > > Also, if the h/w gives me a single packet in > multiple > > locations (i.e. non-contiguous chunks of memory), > can > > socket buffers handle chains of buffers? I am > looking > > for a facility like mbuf's in netbsd where one can > > chain multiple buffers together to make construct > a > > single packet. > > Yes, skb frag list could be used for that but you > don't > want to do that. See above. Copy the data into an > new > skb and reserve any necessary bytes so IP header is > aligned. I.e. if using ethernet header (14 bytes), > do > skb_reserve(skb, 2) before copying the data. > ____________________________________________________________________________________ Looking for a deal? Find great prices on flights and hotels with Yahoo! FareChase. http://farechase.yahoo.com/ - To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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