On Tue, Apr 28, 2020 at 12:34:07PM +0200, Pablo Neira Ayuso wrote: > On Tue, Apr 28, 2020 at 02:33:02PM +1000, Duncan Roe wrote: > > On Mon, Apr 27, 2020 at 07:06:56PM +0200, Pablo Neira Ayuso wrote: > > > 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. > > > > I really do not like the direction this is taking. pktb_build_data() is one of 4 > > new functions you are suggesting, the others being pktb_alloc_head(), > > pktb_reset_network_header() and pktb_set_network_header(). In > > https://www.spinics.net/lists/netfilter-devel/msg65830.html, you asked > > > > > I wonder if all these new functions can be consolidated into one > > > single function, something like: > > > > > > struct pkt_buff *pktb_alloc2(int family, void *head, size_t head_size, void *data, size_t len, size_t extra); > > pktb_alloc2() still has a memcpy which is not needed by people that do > not need to mangle the packet. No it does not. Please look again. There is only a memcpy if the caller specifies extra > 0, in which case she clearly intends to mangle it (perhaps depending on its contents). "depending on its contents" is where the memcpy deferral comes in. pktb_alloc2() verifies that the supplied buffer is big enough (size >= len + extra). The user declared it as a stack variable that size so it will be. With the deferral enhancement, pktb_alloc2() records the buffer address and extra in the enlarged struct pktbuff (extra is needed to tell pktb_mangle how much memory to memset to 0). If pktb_mangle() finds it has to make the packet larger then its original length and the packet is still in its original location then copy it and zero extra. (i.e. pktb_mangle() doesn't just check whether it was asked to make the packet bigger: it might have previously been asked to make it smaller). Also (and this *is* tricky, update relevant pointers in the struct pktbuff). That invalidates any poiners the caller may have obtained from e.g. pktb_data() - see end of email. > > > That's what I have delivered, except for 2 extra args on the end for the packet > > copy buffer. And I get rid of pktb_free(), or at least deprecate and move it off > > the main doc page into the "Other functions" page. > > > > Also pktb_set_network_header() makes no allowance for AF_BRIDGE. > > This is not a problem, you only have to call this function with > ETH_HLEN to set the offset in case of bridge. > > > Can we please just stick with > > > > > struct pkt_buff *pktb_alloc2(int family, void *head, size_t headsize, > > > void *data, size_t len, size_t extra, > > > void *buf, size_t bufsize) > > I'm fine if you still like the simplified pktb_alloc2() call, that's OK. > > [...] > > > 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. > > > > OK - will start on a patch based on > > https://www.spinics.net/lists/netfilter-devel/msg66710.html > > Revisiting, I would prefer to keep things simple. The caller should > make sure that pktb_mangle() has a buffer containing enough room. I > think it's more simple for the caller to allocate a buffer that is > large enough for any mangling. Yes it's more complex. No problem with the buffer - the user gave that to pktb_alloc2(). Problem is that if mangler moves the packet, then any packet pointer the caller had is invalid (points to the un-mangled copy). This applies at all levels, e.g. nfq_udp_get_payload(). There is no way for the mangler functions to address this: it just has to be highlighted in the documentation. Still, I really like the deferred copy enhancement. Your thoughts? Cheers ... Duncan.
