Hi Duncan, On Mon, Apr 27, 2020 at 09:06:14PM +1000, Duncan Roe wrote: > Hi Pablo, > > On Sun, Apr 26, 2020 at 03:23:53PM +0200, Pablo Neira Ayuso wrote: > > Hi Duncan, > > > > This is another turn / incremental update to the pktbuff API based on > > your feedback: > > > > Patch #1 adds pktb_alloc_head() to allocate the pkt_buff structure. > > This patch also adds pktb_build_data() to set up the pktbuff > > data pointer. > > > > Patch #2 updates the existing example to use pktb_alloc_head() and > > pktb_build_data(). > > > > Patch #3 adds a few helper functions to set up the pointer to the > > network header. > > > > Your goal is to avoid the memory allocation and the memcpy() in > > pktb_alloc(). With this scheme, users pre-allocate the pktbuff object > > from the configuration step, and then this object is recycled for each > > packet that is received from the kernel. > > > > Would this update fit for your usecase? > > No, sorry. The show-stopper is, no allowance for the "extra" arg, when you might > want to mangle a packet tobe larger than it was. I see, maybe pktb_build_data() can be extended to take the "extra" arg. Or something like this: void pktb_build_data(struct pkt_buff *pktb, uint8_t *payload, uint32_t size, uint32_t len) where size is the total buffer size, and len is the number of bytes that are in used in the buffer. > For "extra" support, you need something with the sophistication of pktb_malloc2. > If extra == 0, pktb_malloc2 optimises by leaving the packet data where it was. With this patchset, the user is in control of the data buffer memory area that is attached to the pkt_buff head, so you can just allocate the as many extra byte as you require. > Actually pktb_malloc2 doesn't need to make this decision. That can be deferred > to pktb_mangle, which could do the copy if it has been told to expand a packet > and the copy has not already been done (new "copy done" flag in the opaque > struct pkt_buff). I think it's fine if pktb_mangle() deals with this data buffer reallocation in case it needs to expand the packet, a extra patch on top of this should be fine. > My nfq-based accidentally-written ad blocker would benefit from that deferment - > I allow extra bytes in case I have to lengthen a domain name, but most of the > time I'm shortening them. Thanks for explaining.
