On Wed, Jan 01, 2025 at 10:54:37PM +0100, Stefano Brivio wrote: > On Fri, 20 Dec 2024 19:35:30 +1100 > David Gibson wrote: > > > Two places in the code use the packet_get_try() variant on packet_get(). > > The difference is that packet_get_try() passes a NULL 'func' to > > packet_get_do(), which suppresses log messages. The places we use this > > are ones where we expect to sometimes have a failure retreiving the packet > > range, even in normal cases. So, suppressing the log messages seems like > > it makes sense, except: > > > > 1) It suppresses log messages on all errors. We (somewhat) expect to hit > > the case where the requested range is not within the received packet. > > However, it also suppresses message in cases where the requested packet > > index doesn't exist, the requested range has a nonsensical length or > > doesn't lie in even the right vague part of memory. None of those > > latter cases are expected, and the message would be helpful if we ever > > actually hit them. > > > > 2) The suppressed messages aren't actually that disruptive. For the case > > in ip.c, we'd log only if we run out of IPv6 packet before reaching a > > (non-option) L4 header. That shouldn't be the case in normal operation > > so getting a message (at trave level) is not unreasonable. > > For the case in dhcpv6.c we do suppress a message every time we look for > > but don't find a specific DHCPv6 option. That can happen in perfectly > > ok cases, but, again these are trace() level and DHCPv6 transactions > > aren't that common. Suppressing the message for this case doesn't > > seem worth the drawbacks of (1). > > The reason why I implemented packet_get_try() is that the messages from > packet_get_do() indicate serious issues, and if I'm debugging something > by looking at traces it's not great to have messages indicating that we > hit a serious issue while we're simply validating identity associations. I'm not following your argument here. It's exactly because (most of) the message indicate serious issues that I don't want to suppress them. I don't know what you mean by "validating identity associations". > It's not about the amount of logged messages, it's about the type of > message being logged and the distracting noise possibly resulting in a > substantial time waste. > > About 1): dhcpv6_opt() always picks pool index 0, and the base offset > was already checked by the caller. Right, but dhcpv6_opt() is called in a loop, that only stops when it returns NULL. So, by construction the last call to dhcpv6_opt(), which terminates the loop, _will_ have a failing call to packet_get(). At this point - at least assuming a correctly constructed packet - the offset will point to just past the last option, which should be exactly at the end of the packet. > In ipv6_l4hdr(), the index was > already validated by a previous call to packet_get(), and the starting > offset as well. Not AFAICT, the initial packet_get just validates the basic IPv6 header. The calls to packet_get_try() in the loop validate additional IP options. I don't think it will ever fail on a well-constructed packet, but it could on a bogus (or truncated) packet, where the nexthdr field indicates an option that's actually missing. This is kind of my point: it will only trip on a badly constructed packet, in which case I don't think we want to suppress messages. > I guess the main reason to have this patch in this series is to make a > later change simpler, but I'm not sure which one, so I don't know what > to suggest as an alternative. Mostly the next one - making more distinction between the different error severities that can occur here. Having to deal with the possibility of func being NULL complicates things. > > Signed-off-by: David Gibson > > --- > > dhcpv6.c | 2 +- > > ip.c | 2 +- > > packet.c | 18 +++++------------- > > packet.h | 3 --- > > 4 files changed, 7 insertions(+), 18 deletions(-) > > > > diff --git a/dhcpv6.c b/dhcpv6.c > > index 0523bba8..c0d05131 100644 > > --- a/dhcpv6.c > > +++ b/dhcpv6.c > > @@ -271,7 +271,7 @@ static struct opt_hdr *dhcpv6_opt(const struct pool *p, size_t *offset, > > if (!*offset) > > *offset = sizeof(struct udphdr) + sizeof(struct msg_hdr); > > > > - while ((o = packet_get_try(p, 0, *offset, sizeof(*o), &left))) { > > + while ((o = packet_get(p, 0, *offset, sizeof(*o), &left))) { > > unsigned int opt_len = ntohs(o->l) + sizeof(*o); > > > > if (ntohs(o->l) > left) > > diff --git a/ip.c b/ip.c > > index 2cc7f654..e391f81b 100644 > > --- a/ip.c > > +++ b/ip.c > > @@ -51,7 +51,7 @@ char *ipv6_l4hdr(const struct pool *p, int idx, size_t offset, uint8_t *proto, > > if (!IPV6_NH_OPT(nh)) > > goto found; > > > > - while ((o = packet_get_try(p, idx, offset, sizeof(*o), dlen))) { > > + while ((o = packet_get(p, idx, offset, sizeof(*o), dlen))) { > > nh = o->nexthdr; > > hdrlen = (o->hdrlen + 1) * 8; > > > > diff --git a/packet.c b/packet.c > > index bcac0375..c921aa15 100644 > > --- a/packet.c > > +++ b/packet.c > > @@ -112,27 +112,19 @@ void *packet_get_do(const struct pool *p, size_t idx, size_t offset, > > char *ptr; > > > > if (idx >= p->size || idx >= p->count) { > > - if (func) { > > - trace("packet %zu from pool size: %zu, count: %zu, " > > - "%s:%i", idx, p->size, p->count, func, line); > > - } > > + trace("packet %zu from pool size: %zu, count: %zu, %s:%i", > > + idx, p->size, p->count, func, line); > > If you change this, the documentation of the arguments for > packet_get_do() should be updated as well. Fixed. The doc for packet_add_do() also changed, where it was already wrong. > > return NULL; > > } > > > > if (len > PACKET_MAX_LEN) { > > - if (func) { > > - trace("packet data length %zu, %s:%i", > > - len, func, line); > > - } > > + trace("packet data length %zu, %s:%i", len, func, line); > > return NULL; > > } > > > > if (len + offset > p->pkt[idx].iov_len) { > > - if (func) { > > - trace("data length %zu, offset %zu from length %zu, " > > - "%s:%i", len, offset, p->pkt[idx].iov_len, > > - func, line); > > - } > > + trace("data length %zu, offset %zu from length %zu, %s:%i", > > + len, offset, p->pkt[idx].iov_len, func, line); > > return NULL; > > } > > > > diff --git a/packet.h b/packet.h > > index 05d37695..f95cda08 100644 > > --- a/packet.h > > +++ b/packet.h > > @@ -45,9 +45,6 @@ void pool_flush(struct pool *p); > > #define packet_get(p, idx, offset, len, left) \ > > packet_get_do(p, idx, offset, len, left, __func__, __LINE__) > > > > -#define packet_get_try(p, idx, offset, len, left) \ > > - packet_get_do(p, idx, offset, len, left, NULL, 0) > > - > > #define PACKET_POOL_DECL(_name, _size, _buf) \ > > struct _name ## _t { \ > > char *buf; \ > -- David Gibson (he or they) | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you, not the other way | around. http://www.ozlabs.org/~dgibson