> -----Original Message----- > From: Alexander Duyck [mailto:alexander.h.duyck@xxxxxxxxxx] > Sent: Thursday, October 16, 2014 11:28 PM > To: Pan Jiafei-B37022; Eric Dumazet > Cc: David Miller; jkosina@xxxxxxx; netdev@xxxxxxxxxxxxxxx; Li Yang-Leo-R58472; > linux-doc@xxxxxxxxxxxxxxx > Subject: Re: [PATCH] net: use hardware buffer pool to allocate skb > > > On 10/15/2014 10:15 PM, Jiafei.Pan@xxxxxxxxxxxxx wrote: > >> -----Original Message----- > >> From: Eric Dumazet [mailto:eric.dumazet@xxxxxxxxx] > >> Sent: Thursday, October 16, 2014 12:15 PM > >> To: Pan Jiafei-B37022 > >> Cc: David Miller; jkosina@xxxxxxx; netdev@xxxxxxxxxxxxxxx; Li Yang-Leo-R58472; > >> linux-doc@xxxxxxxxxxxxxxx > >> Subject: Re: [PATCH] net: use hardware buffer pool to allocate skb > >> > >> On Thu, 2014-10-16 at 02:17 +0000, Jiafei.Pan@xxxxxxxxxxxxx wrote: > >> > >>> Thanks for your comments and suggestion. In my case, I want to build skb > >>> from hardware block specified memory, I only can see two ways, one is > modified > >>> net card driver replace common skb allocation function with my specially > >>> functions, another way is to hack common skb allocation function in which > >>> redirect to my specially functions. My patch is just for the second way. > >>> Except these two ways, would you please give me some advice for some other > >>> ways for my case? Thanks > >> I suggest you read drivers/net/ethernet numerous examples. > >> > >> No need to change anything in net/* or include/*, really. > >> > >> For a start, look at drivers/net/ethernet/intel/igb/igb_main.c > >> > >> Mentioning 'hack' in your mails simply should hint you are doing > >> something very wrong. > >> > >> What makes you think your hardware is so special ? > >> > > In fact, I am developing a bridge driver, it can bridge between any other the > > third party net card and my own net card. My target is to let any other the > > third party net card can directly use my own net card specified buffer, then > > there will be no memory copy in the whole bridge process. > > By the way, I don’t see any similar between igb_main.c and my case. And also > > My bridge also can’t implemented with "skb frag" in order to aim at zero > memory > > copy. > > I think the part you are not getting is that is how buffers are > essentially handled now. [Pan Jiafei] Hi, Alex, thanks for your comments. I don’t confirm that you have catch my concerns. For example, I want to add igb net card into my bridge, and want to igb net driver allocate skb by using my specified memory address, but I don’t want to modify igb net driver directly, how to do this in my bridge drivers? Thanks, Jiafei. So for example in the case if igb the only > part we have copied out is usually the header, or the entire frame in > the case of small packets. This has to happen in order to allow for > changes to the header for routing and such. Beyond that the frags that > are passed are the buffers that igb is still holding onto. So > effectively what the other device transmits in a bridging/routing > scenario is my own net card specified buffer plus the copied/modified > header. > > For a brief period igb used build_skb but that isn't valid on most > systems as memory mapped for a device can be overwritten if the page is > unmapped resulting in any changes to the header for routing/bridging > purposes being invalidated. Thus we cannot use the buffers for both the > skb->data header which may be changed and Rx DMA simultaneously. > > Thanks, > > Alex ��.n��������+%������w��{.n�����{����* jg��� �����ݢj����G���� ���j:+v���w�m������w�������h�����٥
