Both tcp.c and tcp_splice.c define CONN_IDX() variants to find the index
of their connection structures in the connection table, now become the
unified flow table. We can easily combine these into a common helper.
While we're there, add some trickery for some additional type safety.
They also define their own CONN() versions, which aren't so easily combined
since they need to return different types, but we can have them use a
common helper.
In the process, we standardise on always using an unsigned type to store
the connection / flow index, which makes more sense. tcp.c's conn_at_idx()
remains for now, but we change its parameter to unsigned to match. That in
turn means we can remove a check for negative values from it.
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
We want to generalise "connection" tracking to things other than true TCP
connections. Continue implenenting this by renaming the TCP connection
table to the "flow table" and moving it to flow.c. The definitions are
split between flow.h and flow_table.h - we need this separation to avoid
circular dependencies: the definitions in flow.h will be needed by many
headers using the flow mechanism, but flow_table.h needs all those protocol
specific headers in order to define the full flow table entry.
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Currently TCP connections use a 1-bit selector, 'spliced', to determine the
rest of the contents of the structure. We want to generalise the TCP
connection table to other types of flows in other protocols. Make a start
on this by replacing the tcp_conn_common structure with a new flow_common
structure with an enum rather than a simple boolean indicating the type of
flow.
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Types size_t and ssize_t are not necessarily long, it depends on the
architecture.
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
valgrind complains if we pass a NULL buffer to recv(), even if we use
MSG_TRUNC, in which case it's actually safe. For a long time we've had
a valgrind suppression for this. It singles out the recv() in
tcp_sock_consume(), the only place we use MSG_TRUNC.
However, tcp_sock_consume() only has a single caller, which makes it a
prime candidate for inlining. If inlined, it won't appear on the stack and
valgrind won't match the correct suppression.
It appears that certain compiler versions (for example gcc-13.2.1 in
Fedora 39) will inline this function even with the -O0 we use for valgrind
builds. This breaks the suppression leading to a spurious failure in the
tests.
There's not really any way to adjust the suppression itself without making
it overly broad (we don't want to match other recv() calls). So, as a hack
explicitly prevent inlining of this function when we're making a valgrind
build. To accomplish this add an explicit -DVALGRIND when making such a
build.
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
tcp_port_rebind() is desgined to be called from NS_CALL() and has two
disjoint cases: one where it enters the namespace (outbound forwards) and
one where it doesn't (inbound forwards).
We only actually need the NS_CALL() framing for the outbound case, for
inbound we can just call tcp_port_do_rebind() directly. So simplify
tcp_port_rebind() to tcp_port_rebind_outbound(), allowing us to eliminate
an awkward parameters structure.
With that done we can safely rename tcp_port_do_rebind() to
tcp_port_rebind() for brevity.
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
tcp_port_rebind() has two cases with almost but not quite identical code.
Simplify things a bit by factoring this out into a single parameterised
helper, tcp_port_do_rebind().
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
On the L2 tap side, we see TCP headers and know the TCP window that the
ultimate receiver is advertising. In order to avoid unnecessary buffering
within passt/pasta (or by the kernel on passt/pasta's behalf) we attempt
to advertise that window back to the original sock-side sender using
TCP_WINDOW_CLAMP.
However, TCP_WINDOW_CLAMP just doesn't work like this. Prior to kernel
commit 3aa7857fe1d7 ("tcp: enable mid stream window clamp"), it simply
had no effect on established sockets. After that commit, it does affect
established sockets but doesn't behave the way we need:
* It appears to be designed only to shrink the window, not to allow it to
re-expand.
* More importantly, that commit has a serious bug where if the
setsockopt() is made when the existing kernel advertised window for the
socket happens to be zero, it will now become locked at zero, stopping
any further data from being received on the socket.
Since this has never worked as intended, simply remove it. It might be
possible to re-implement the intended behaviour by manipulating SO_RCVBUF,
so we leave a comment to that effect.
This kernel bug is the underlying cause of both the linked passt bug and
the linked podman bug. We attempted to fix this before with passt commit
d3192f67 ("tcp: Force TCP_WINDOW_CLAMP before resetting STALLED flag").
However while that commit masked the bug for some cases, it didn't really
address the problem.
Fixes: d3192f67c4 ("tcp: Force TCP_WINDOW_CLAMP before resetting STALLED flag")
Link: https://github.com/containers/podman/issues/20170
Link: https://bugs.passt.top/show_bug.cgi?id=74
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
tcp_clamp_window() is _mostly_ about using TCP_WINDOW_CLAMP to control the
sock side advertised window, but it is also responsible for actually
updating the conn->wnd_from_tap value.
Rename to tcp_tap_window_update() to reflect that broader purpose, and pull
the logic that's not TCP_WINDOW_CLAMP related out to the front.
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
logmsg() takes printf like arguments, but because it's not a built in, the
compiler won't generate warnings if the format string and parameters don't
match. Enable those by using the format attribute.
Strictly speaking this is a gcc extension, but I believe it is also
supported by some other common compilers. We already use some other
attributes in various places. For now, just use it and we can worry about
compilers that don't support it if it comes up.
This exposes some warnings from existing callers, both in gcc and in
clang-tidy:
- Some are straight out bugs, which we correct
- It's occasionally useful to invoke the logging functions with an empty
string, which gcc objects to, so disable that specific warning in the
Makefile
- Strictly speaking the C standard requires that the parameter for a %p
be a (void *), not some other pointer type. That's only likely to cause
problems in practice on weird architectures with different sized
representations for pointers to different types. Nonetheless add the
casts to make it happy.
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Use of tcp_l2_mh has been removed in commit 38fbfdbcb9,
but its declaration and initialization are always in the code.
Remove them as they are useless.
Fixes: 38fbfdbcb9 ("tcp: Get rid of iov with cached MSS, drop sendmmsg(), add deferred flush")
Signed-off-by: Laurent Vivier <lvivier@redhat.com>
Acked-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
For now, packets passed to the various *_tap_handler() functions always
come from the single "tap" interface. We want to allow the possibility to
broaden that in future. As preparation for that, have the code in tap.c
pass the pif id of the originating interface to each of those handler
functions.
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
For certain socket types, we record in the epoll ref whether they're
sockets in the namespace, or on the host. We now have the notion of "pif"
to indicate what "place" a socket is associated with, so generalise the
simple one-bit 'ns' to a pif id.
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
get_bound_ports_*() now only use their context and ns parameters to
determine which forwarding maps they're operating on. Each function needs
the map they're actually updating, as well as the map for the other
direction, to avoid creating forwarding loops. The UDP function also
requires the corresponding TCP map, to implement the behaviour where we
forward UDP ports of the same number as bound TCP ports for tools like
iperf3.
Passing those maps directly as parameters simplifies the code without
making the callers life harder, because those already know the relevant
maps. IMO, invoking these functions in terms of where they're looking for
updated forwarding also makes more logical sense than in terms of where
they're looking for bound ports. Given that new way of looking at the
functions, also rename them to port_fwd_scan_*().
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Currently get_bound_ports() takes a parameter to determine if it scans for
UDP or TCP bound ports, but in fact there's almost nothing in common
between those two paths. The parameter appears primarily to have been
a convenience for when we needed to invoke this function via NS_CALL().
Now that we don't need that, split it into separate TCP and UDP versions.
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
When we want to scan for bound ports in the namespace we use NS_CALL() to
run get_bound_ports() in the namespace. However, the only thing it
actually needed to be in the namespace for was to open the /proc/net file
it was scanning. Since we now always pre-open those, we no longer need
to switch to the namespace for the actual get_bound_ports() calls.
That in turn means that tcp_port_detect() doesn't need to run in the ns
either, and we can just replace it with inline calls to get_bound_ports().
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
The implementation of scanning /proc files to do automatic port forwarding
is a bit awkwardly split between procfs_scan_listen() in util.c,
get_bound_ports() and related functions in conf.c and the initial setup
code in conf().
Consolidate all of this into port_fwd.h, which already has some related
definitions, and a new port_fwd.c.
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
...so that we'll retry sending them, instead of more-or-less silently
dropping them. This happens quite frequently if our sending buffer on
the UNIX domain socket is heavily constrained (for instance, by the
208 KiB default memory limit).
It might be argued that dropping frames is part of the expected TCP
flow: we don't dequeue those from the socket anyway, so we'll
eventually retransmit them.
But we don't need the receiver to tell us (by the way of duplicate or
missing ACKs) that we couldn't send them: we already know as
sendmsg() reports that. This seems to considerably increase
throughput stability and throughput itself for TCP connections with
default wmem_max values.
Unfortunately, the 16 bits left as padding in the frame descriptors
we use internally aren't enough to uniquely identify for which
connection we should update sequence numbers: create a parallel
array of pointers to sequence numbers and L4 lengths, of
TCP_FRAMES_MEM size, and go through it after calling sendmsg().
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
It looks like we need it as workaround for this situation, readily
reproducible at least with a 6.5 Linux kernel, with default rmem_max
and wmem_max values:
- an iperf3 client on the host sends about 160 KiB, typically
segmented into five frames by passt. We read this data using
MSG_PEEK
- the iperf3 server on the guest starts receiving
- meanwhile, the host kernel advertised a zero-sized window to the
sender, as expected
- eventually, the guest acknowledges all the data sent so far, and
we drop it from the buffer, courtesy of tcp_sock_consume(), using
recv() with MSG_TRUNC
- the client, however, doesn't get an updated window value, and
even keepalive packets are answered with zero-window segments,
until the connection is closed
It looks like dropping data from a socket using MSG_TRUNC doesn't
cause a recalculation of the window, which would be expected as a
result of any receiving operation that invalidates data on a buffer
(that is, not with MSG_PEEK).
Strangely enough, setting TCP_WINDOW_CLAMP via setsockopt(), even to
the previous value we clamped to, forces a recalculation of the
window which is advertised to the sender.
I couldn't quite confirm this issue by following all the possible
code paths in the kernel, yet. If confirmed, this should be fixed in
the kernel, but meanwhile this workaround looks robust to me (and it
will be needed for backward compatibility anyway).
Reported-by: Matej Hrica <mhrica@redhat.com>
Link: https://bugs.passt.top/show_bug.cgi?id=74
Analysed-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
cppcheck 2.12.0 (and maybe some other versions) things this if condition
is always true, which is demonstrably not true. Work around the bug for
now.
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Newer versions of cppcheck (as of 2.12.0, at least) added a warning for
pointers which could be declared to point at const data, but aren't.
Based on that, make many pointers throughout the codebase const.
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
We have a bunch of variants of the siphash functions for different data
sizes. The callers, in tcp.c, need to pack the various values they want to
hash into a temporary structure, then call the appropriate version. We can
avoid the copy into the temporary by directly using the incremental
siphash functions.
The length specific hash functions also have an undocumented constraint
that the data pointer they take must, in fact, be aligned to avoid
unaligned accesses, which may cause crashes on some architectures.
So, prefer the incremental approach and remove the length-specific
functions.
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Some of the siphas_*b() functions return 64-bit results, others 32-bit
results, with no obvious pattern. siphash_32b() also appears to do this
incorrectly - taking the 64-bit hash value and simply returning it
truncated, rather than folding the two halves together.
Since SipHash proper is defined to give a 64-bit hash, make all of them
return 64-bit results. In the one caller which needs a 32-bit value,
tcp_seq_init() do the fold down to 32-bits ourselves.
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
We have several workarounds for a clang-tidy bug where the checker doesn't
recognize that a number of system calls write to - and therefore initialise
- a socket address. We can't neatly use a suppression, because the bogus
warning shows up some time after the actual system call, when we access
a field of the socket address which clang-tidy erroneously thinks is
uninitialised.
Consolidate these workarounds into one place by using macros to implement
wrappers around affected system calls which add a memset() of the sockaddr
to silence clang-tidy. This removes the need for the individual memset()
workarounds at the callers - and the somewhat longwinded explanatory
comments.
We can then use a #define to not include the hack in "real" builds, but
only consider it for clang-tidy.
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
A classic gotcha of the standard C library is that its unwise to call any
variable 'index' because it will shadow the standard string library
function index(3). This can cause warnings from cppcheck amongst others,
and it also means that if the variable is removed you tend to get confusing
type errors (or sometimes nothing at all) instead of a nice simple "name is
not defined" error.
Strictly speaking this only occurs if <string.h> is included, but that
is so common that as a rule it's best to just avoid it always. We
have a number of places which hit this trap, so rename variables and
parameters to avoid it.
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
The reporter is running a SMTP server behind pasta, and the client
waits for the server's banner before sending any data. In turn, the
server waits for our ACK after sending SYN,ACK, which never comes.
If we use the ACK_IF_NEEDED indication to tcp_send_flag(), given that
there's no pending data, we delay sending the ACK segment at the end
of the three-way handshake until we have some data to send to the
server.
This was actually intended, as I thought we would lower the latency
for new connections, but we can't assume that the client will start
sending data first (SMTP is the typical example where this doesn't
happen).
And, trying out this patch with SSH (where the client starts sending
data first), the reporter actually noticed we have a lower latency
by forcing an ACK right away. Comparing a capture before the patch:
13:07:14.007704 IP 10.1.2.1.42056 > 10.1.2.140.1234: Flags [S], seq 1797034836, win 65535, options [mss 4096,nop,wscale 7], length 0
13:07:14.007769 IP 10.1.2.140.1234 > 10.1.2.1.42056: Flags [S.], seq 2297052481, ack 1797034837, win 65480, options [mss 65480,nop,wscale 7], length 0
13:07:14.008462 IP 10.1.2.1.42056 > 10.1.2.140.1234: Flags [.], seq 1:22, ack 1, win 65535, length 21
13:07:14.008496 IP 10.1.2.140.1234 > 10.1.2.1.42056: Flags [.], ack 22, win 512, length 0
13:07:14.011799 IP 10.1.2.140.1234 > 10.1.2.1.42056: Flags [P.], seq 1:515, ack 22, win 512, length 514
and after:
13:10:26.165364 IP 10.1.2.1.59508 > 10.1.2.140.1234: Flags [S], seq 4165939595, win 65535, options [mss 4096,nop,wscale 7], length 0
13:10:26.165391 IP 10.1.2.140.1234 > 10.1.2.1.59508: Flags [S.], seq 985607380, ack 4165939596, win 65480, options [mss 65480,nop,wscale 7], length 0
13:10:26.165418 IP 10.1.2.1.59508 > 10.1.2.140.1234: Flags [.], ack 1, win 512, length 0
13:10:26.165683 IP 10.1.2.1.59508 > 10.1.2.140.1234: Flags [.], seq 1:22, ack 1, win 512, length 21
13:10:26.165698 IP 10.1.2.140.1234 > 10.1.2.1.59508: Flags [.], ack 22, win 512, length 0
13:10:26.167107 IP 10.1.2.140.1234 > 10.1.2.1.59508: Flags [P.], seq 1:515, ack 22, win 512, length 514
the latency between the initial SYN segment and the first data
transmission actually decreases from 792µs to 334µs. This is not
statistically relevant as we have a single measurement, but it can't
be that bad, either.
Reported-by: cr3bs (from IRC)
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
When the guest tries to establish a connection, it could give up on it by
sending a FIN,ACK instead of a plain ACK to our SYN,ACK. It could then
make a new attempt to establish a connection with the same addresses and
ports with a new SYN.
Although it's unlikely, it could send the 2nd SYN very shortly after the
FIN,ACK resulting in both being received in the same batch of packets from
the tap interface.
Currently, we don't handle that correctly, when we receive a FIN,ACK on a
not fully established connection we discard the remaining packets in the
batch, and so will never process the 2nd SYN. Correct this by returning
1 from tcp_tap_handler() in this case, so we'll just consume the FIN,ACK
and continue to process the rest of the batch.
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
There are a number of conditions where we will issue a TCP RST in response
to something unexpected we received from the tap interface. These occur in
both tcp_data_from_tap() and tcp_tap_handler(). In tcp_tap_handler() use
a 'goto out of line' technique to consolidate all these paths into one
place. For the tcp_data_from_tap() cases use a negative return code and
direct that to the same path in tcp_tap_handler(), its caller.
In this case we want to discard all remaining packets in the batch we have
received: even if they're otherwise good, they'll be invalidated when the
guest receives the RST we're sending. This is subtly different from the
case where we *receive* an RST, where we could in theory get a new SYN
immediately afterwards. Clarify that with a common on the now common
reset path.
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Although it's unlikely in practice, the guest could theoretically
reset one TCP connection then immediately start a new one with the
same addressses and ports, such that we get an RST then a SYN in the
same batch of received packets in tcp_tap_handler().
We don't correctly handle that unlikely case, because when we receive
the RST, we discard any remaining packets in the batch so we'd never
see the SYN. This could happen in either tcp_tap_handler() or
tcp_data_from_tap(). Correct that by returning 1, so that the caller
will continue calling tcp_tap_handler() on subsequent packets allowing
us to process any subsequent SYN.
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Currently tcp_data_from_tap() is assumed to consume all packets remaining
in the packet pool it is given. However there are some edge cases where
that's not correct. In preparation for fixing those, change it to return
a count of packets consumed and use that in its caller.
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
>From a practical point of view, when a TCP connection ends, whether by
FIN or by RST, we set the CLOSED event, then some time later we remove the
connection from the hash table and clean it up. However, from a protocol
point of view, once it's closed, it's gone, and any new packets with
matching addresses and ports are either forming a new connection, or are
invalid packets to discard.
Enforce these semantics in the TCP hash logic by never hash matching closed
connections.
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Both tcp_data_from_tap() and tcp_tap_handler() call packet_get() to get
the entire L4 packet length, then immediately call it again to check that
the packet is long enough to include a TCP header. The features of
packet_get() let us easily combine these together, we just need to adjust
the length slightly, because we want the value to include the TCP header
length.
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
In both tap4_handler() and tap6_handler(), once we've sorted incoming l3
packets into "sequences", we then step through all the packets in each TCP
sequence calling tcp_tap_handler(). Or so it appears.
In fact, tcp_tap_handler() doesn't take an index and always looks at packet
0 of the sequence, except when it calls tcp_data_from_tap() to process
data packets. It appears to be written with the idea that the struct pool
is a queue, from which it consumes packets as it processes them, but that's
not how the pool data structure works - they are more like an array of
packets.
We only get away with this, because setup packets for TCP tend to come in
separate batches (because we need to reply in between) and so we only get
a bunch of packets for the same connection together when they're data
packets (tcp_data_from_tap() has its own loop through packets).
Correct this by adding an index parameter to tcp_tap_handler() and altering
the loops in tap.c to step through the pool properly.
Link: https://bugs.passt.top/show_bug.cgi?id=68
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
tcp_defer_handler() performs a potentially expensive linear scan of the
connection table. So, to mitigate the cost of that we skip if if we're not
under at least moderate pressure: either 30% of available connections or
30% (estimated) of available fds used.
But, the calculation for this has been broken since it was introduced: we
calculate "max_conns" based on c->tcp.conn_count, not TCP_MAX_CONNS,
meaning we only exit early if conn_count is less than 30% of itself, i.e.
never.
If that calculation is "corrected" to be based on TCP_MAX_CONNS, it
completely tanks the TCP CRR times for passt - from ~60ms to >1000ms on my
laptop. My guess is that this is because in the case of many short lived
connections, we're letting the table become much fuller before compacting
it. That means that other places which perform a table scan now have to
do much, much more.
For the time being, simply remove the tests, since they're not doing
anything useful. We can reintroduce them more carefully if we see a need
for them.
This also removes the only user of c->tcp.splice_conn_count, so that can
be removed as well.
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
The in_epoll boolean is one of only two fields (currently) in the common
structure shared between tap and spliced connections. It seems like it
belongs there, because both tap and spliced connections use it, and it has
roughly the same meaning.
Roughly, however, isn't exactly: which fds this flag says are in the epoll
varies between the two connection types, and are in type specific fields.
So, it's only possible to meaningfully use this value locally in type
specific code anyway.
This common field is going to get in the way of more widespread
generalisation of connection / flow tracking, so move it to separate fields
in the tap and splice specific structures.
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Because packets sent on the tap interface will always be going to the
guest/namespace, we more-or-less know what address they'll be going to. So
we pre-fill this destination address in our header buffers for IPv4. We
can't do the same for IPv6 because we could need either the global or
link-local address for the guest. In future we're going to want more
flexibility for the destination address, so this pre-filling will get in
the way.
Change the flow so we always fill in the IPv4 destination address for each
packet, rather than prefilling it from proto_update_l2_buf(). In fact for
TCP we already redundantly filled the destination for each packet anyway.
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
We partially prepopulate IP and TCP header structures including, amongst
other things the destination address, which for IPv4 is always the known
address of the guest/namespace. We partially precompute both the IPv4
header checksum and the TCP checksum based on this.
In future we're going to want more flexibility with controlling the
destination for IPv4 (as we already do for IPv6), so this precomputed value
gets in the way. Therefore remove the IPv4 destination from the
precomputed checksum and fold it into the checksum update when we actually
send a packet.
Doing this means we no longer need to recompute those partial sums when
the destination address changes ({tcp,udp}_update_l2_buf()) and instead
the computation can be moved to compile time. This means while we perform
slightly more computations on each packet, we slightly reduce the amount of
memory we need to access.
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
In tcp_seq_init() the meaning of "src" and "dst" isn't really clear since
it's used for connections in both directions. However, these values are
just feeding a hash, so as long as we're consistent and include all the
information we want, it doesn't really matter.
Oddly, for the "src" side we supply the (tap side) forwarding address but
the (tap side) endpoint port. This again doesn't really matter, but it's
confusing. So swap this with dstport, so "src" is always forwarding
and "dst" is always endpoint.
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
In a number of places the comments and variable names we use to describe
addresses and ports are ambiguous. It's not sufficient to describe a port
as "tap-facing" or "socket-facing", because on both the tap side and the
socket side there are two ports for the two ends of the connection.
Similarly, "local" and "remote" aren't particularly helpful, because it's
not necessarily clear whether we're talking from the point of view of the
guest/namespace, the host, or passt itself.
This patch makes a number of changes to be more precise about this. It
introduces two new terms in aid of this:
A "forwarding" address (or port) refers to an address which is local
from the point of view of passt itself. That is a source address for
traffic sent by passt, whether it's to the guest via the tap interface
or to a host on the internet via a socket.
The "endpoint" address (or port) is the reverse: a remote address
from passt's point of view, the destination address for traffic sent
by passt.
Between them the "side" (either tap/guest-facing or sock/host-facing)
and forwarding vs. endpoint unambiguously describes which address or
port we're talking about.
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
The tap code passes the IPv4 or IPv6 destination address of packets it
receives to the protocol specific code. Currently that protocol code
doesn't use the source address, but we want it to in future. So, in
preparation, pass the IPv4/IPv6 source address of tap packets to those
functions as well.
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
tcp_sock_handler() handles both listening TCP sockets, and connected TCP
sockets, but what it needs to do in those cases has essentially nothing in
common. Therefore, give listening sockets their own epoll_type value and
dispatch directly to their own handler from the top level. Furthermore,
the two handlers need essentially entirely different information from the
reference: we re-(ab)used the index field in the tcp_epoll_ref to indicate
the port for the listening socket, but that's not the same meaning. So,
switch listening sockets to their own reference type which we can lay out
as we please. That lets us remove the listen and outbound fields from the
normal (connected) tcp_epoll_ref, reducing it to just the connection table
index.
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
tcp_sock_handler() actually handles several different types of fd events.
This includes timerfds that aren't sockets at all. The handling of these
has essentially nothing in common with the other cases. So, give the
TCP timers there own epoll_type value and dispatch directly to their
handler. This also means we can remove the timer field from tcp_epoll_ref,
the information it encoded is now implicit in the epoll_type value.
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
The epoll_ref type includes fields for the IP protocol of a socket, and the
socket fd. However, we already have a few things in the epoll which aren't
protocol sockets, and we may have more in future. Rename these fields to
an abstract "fd type" and file descriptor for more generality.
Similarly, rather than using existing IP protocol numbers for the type,
introduce our own number space. For now these just correspond to the
supported protocols, but we'll expand on that in future.
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
union epoll_ref has a deeply nested set of structs and unions to let us
subdivide it into the various different fields we want. This means that
referencing elements can involve an awkward long string of intermediate
fields.
Using C11 anonymous structs and unions lets us do this less clumsily.
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
In practical terms, passt doesn't benefit from the additional
protection offered by the AGPL over the GPL, because it's not
suitable to be executed over a computer network.
Further, restricting the distribution under the version 3 of the GPL
wouldn't provide any practical advantage either, as long as the passt
codebase is concerned, and might cause unnecessary compatibility
dilemmas.
Change licensing terms to the GNU General Public License Version 2,
or any later version, with written permission from all current and
past contributors, namely: myself, David Gibson, Laine Stump, Andrea
Bolognani, Paul Holzinger, Richard W.M. Jones, Chris Kuhn, Florian
Weimer, Giuseppe Scrivano, Stefan Hajnoczi, and Vasiliy Ulyanov.
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Since commit cc6d8286d1 ("tcp: Reset ACK_FROM_TAP_DUE flag only as
needed, update timer"), we don't clear ACK_FROM_TAP_DUE whenever we
process an ACK segment, but, more correctly, only if we're really not
waiting for a further ACK segment, that is, only if the acknowledged
sequence matches what we sent.
In the new function implementing this, tcp_update_seqack_from_tap(),
we also reset the retransmission counter and store the updated ACK
sequence. Both should be done iff forward progress is acknowledged,
implied by the fact that the new ACK sequence is greater than the
one we previously stored.
At that point, it looked natural to also include the statements that
clear and set the ACK_FROM_TAP_DUE flag inside the same conditional
block: if we're not making forward progress, the need for an ACK, or
lack thereof, should remain unchanged.
There might be cases where this isn't true, though: without the
previous commit 4e73e9bd65 ("tcp: Don't special case the handling
of the ack of a syn"), this would happen if a tap-side client
initiated a connection, and the server didn't send any data.
At that point we would never, in the established state of the
connection, call tcp_update_seqack_from_tap() with reported forward
progress.
That issue itself is fixed by the previous commit, now, but clearing
ACK_FROM_TAP_DUE only on ACK sequence progress doesn't really follow
any logic.
Clear the ACK_FROM_TAP_DUE flag regardless of reported forward
progress. If we clear it when it's already unset, conn_flag() will do
nothing with it.
This doesn't fix any known functional issue, rather a conceptual one.
Fixes: cc6d8286d1 ("tcp: Reset ACK_FROM_TAP_DUE flag only as needed, update timer")
Reported-by: David Gibson <david@gibson.dropbear.id.au>
Analysed-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
TCP treats the SYN packets as though they occupied 1 byte in the logical
data stream described by the sequence numbers. That is, the very first ACK
(or SYN-ACK) each side sends should acknowledge a sequence number one
greater than the initial sequence number given in the SYN or SYN-ACK it's
responding to.
In passt we were tracking that by advancing conn->seq_to_tap by one when
we send a SYN or SYN-ACK (in tcp_send_flag()). However, we also
initialized conn->seq_ack_from_tap, representing the acks we've already
seen from the tap side, to ISN+1, meaning we treated it has having
acknowledged the SYN before it actually did.
There were apparently reasons for this in earlier versions, but it causes
problems now. Because of this when we actually did receive the initial ACK
or SYN-ACK, we wouldn't see the acknoweldged serial number as advancing,
and so wouldn't clear the ACK_FROM_TAP_DUE flag.
In most cases we'd get away because subsequent packets would clear the
flag. However if one (or both) sides didn't send any data, the other side
would (correctly) keep sending ISN+1 as the acknowledged sequence number,
meaning we would never clear the ACK_FROM_TAP_DUE flag. That would mean
we'd treat the connection as if we needed to retransmit (although we had
0 bytes to retransmit), and eventaully (after around 30s) reset the
connection due to too many retransmits. Specifically this could cause the
iperf3 throughput tests in the testsuite to fail if set for a long enough
test period.
Correct this by initializing conn->seq_ack_from_tap to the ISN and only
advancing it when we actually get the first ACK (or SYN-ACK).
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Comments suggest that this should only be called for an ESTABLISHED
connection. However, it's non-trivial to ascertain that from the actual
control flow in the caller. Add an ASSERT() to make it very clear that
this is only called in ESTABLISHED state.
In fact, there were some circumstances where it could be called on a CLOSED
connection. In a sense that is "established", but with that assert this
does require specific (trivial) handling to avoid a spurious abort().
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
