The commit updates the style of function comments by adding parentheses
to function names in the descriptions where they are missing.

Done with:

---------8<------ fix_function_name.awk ---------8<------
/^\/\*\*/ {
    check_next = 1;
    print $0
    next
}
check_next == 1 && / \* struct/ {
    check_next = 0
    print $0
    next
}
check_next == 1 && / \* enum/ {
    check_next = 0
    print $0
    next
}
check_next == 1 && /^ \* [^ (]* -/ {
   modified_line = gensub(/^ \* ([^ ]*) -(.*)$/, " * \\1() -\\2", "g", $0)
   print modified_line
   check_next = 0;
   next
}
{
    print $0
    check_next = 0
}
---------8<------ fix_function_name.awk ---------8<------

Then

for file in *.[ch]; do
    cp ${file} ${file}.tmp && \
    awk -f fix_function_name.awk ${file}.tmp > ${file}
done

Signed-off-by: Laurent Vivier <lvivier@redhat.com>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

We always use imperative (no 'Returns:'), no tab after the ':' and
only one space, the first character is always lowercase.

This is fixed with:

 sed -i "s/Returns:/Return:/;s/Return:    /Return: /;s/Return:  */Return: /;s/Return: \([A-Z]\)/Return: \L\1/" *.[ch]

And manually updated to fix alignment of multiline comment and words
that must keep uppercase (like IPv4, TCP, UDP, Layer-4).

Signed-off-by: Laurent Vivier <lvivier@redhat.com>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

Several of the exposed functions in checksum.h are no longer directly used.
Remove them from the header, and make static.  In particular sum_16b()
should not be used outside: generally csum_unfolded() should be used which
will automatically use either the AVX2 optimized version or sum_16b() as
necessary.

csum_fold() and csum() could have external uses, but they're not used right
now.  We can expose them again if we need to.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

csum_unfolded() must call csum_avx2() with a 32byte aligned base address.

To be able to do that if the buffer is not correctly aligned,
it splits the buffers in 2 parts, the second part is 32byte aligned and
can be used with csum_avx2(), the first part is the remaining part, that
is not 32byte aligned and we use sum_16b() to compute the checksum.

A problem appears if the length of the first part is odd because
the checksum is using 16bit words to do the checksum.

If the length is odd, when the second part is computed, all words are
shifted by 1 byte, meaning weight of upper and lower byte is swapped.

For instance a 13 bytes buffer:

bytes:

aa AA bb BB cc CC dd DD ee EE ff FF gg

16bit words:

AAaa BBbb CCcc DDdd EEee FFff 00gg

If we don't split the sequence, the checksum is:

AAaa + BBbb + CCcc + DDdd + EEee + FFff + 00gg

If we split the sequence with an even length for the first part:

(AAaa + BBbb) + (CCcc + DDdd + EEee + FFff + 00gg)

But if the first part has an odd length:

(AAaa + BBbb + 00cc) + (ddCC + eeDD + ffEE + ggFF)

To avoid the problem, do not call csum_avx2() if the first part cannot
have an even length, and compute the checksum of all the buffer using
sum_16b().

This is slower but it can only happen if the buffer base address is odd,
and this can only happen if the binary is built using '-Os', and that
means we have chosen to prioritize size over speed.

Reported-by: Mike Jones <mike@mjones.io>
Link: https://bugs.passt.top/show_bug.cgi?id=108
Signed-off-by: Laurent Vivier <lvivier@redhat.com>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
[sbrivio: Added comment explaining why we check for pad & 1]
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

We usually want to checksum only the tail part of a frame, excluding at
least some headers.  csum_iov() does that for a frame represented as an
IO vector, not actually summing the entire IO vector.  We now have struct
iov_tail to explicitly represent this construct, so replace csum_iov()
with csum_iov_tail() taking that representation rather than 3 parameters.

We propagate the same change to csum_udp4() and csum_udp6() which take
similar parameters.  This slightly simplifies the code, and will allow some
further simplifications as struct iov_tail is more widely used.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

As for tcp_update_check_tcp4()/tcp_update_check_tcp6(),
change csum_udp4() and csum_udp6() to use an iovec array.

Signed-off-by: Laurent Vivier <lvivier@redhat.com>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

TCP header and payload are supposed to be in the same buffer,
and tcp_update_check_tcp4()/tcp_update_check_tcp6() compute
the checksum from the base address of the header using the
length of the IP payload.

In the future (for vhost-user) we need to dispatch the TCP header and
the TCP payload through several buffers. To be able to manage that, we
provide an iovec array that points to the data of the TCP frame.
We provide also an offset to be able to provide an array that contains
the TCP frame embedded in an lower level frame, and this offset points
to the TCP header inside the iovec array.

Signed-off-by: Laurent Vivier <lvivier@redhat.com>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

The offset allows any headers that are not part of the data
to checksum to be skipped.

Signed-off-by: Laurent Vivier <lvivier@redhat.com>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

At various points we need to track the lengths of a packet including or
excluding various different sets of headers.  We don't always use the same
variable names for doing so.  Worse in some places we use the same name
for different things: e.g. tcp_fill_headers[46]() use ip_len for the
length including the IP headers, but then tcp_send_flag() which calls it
uses it to mean the IP payload length only.

To improve clarity, standardise on these names:
   dlen:		L4 protocol payload length ("data length")
   l4len:		plen + length of L4 protocol header
   l3len:		l4len + length of IPv4/IPv6 header
   l2len:		l3len + length of L2 (ethernet) header

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

csum_ip4_header() takes the packet length as a network endian value.  In
general it's very error-prone to pass non-native-endian values as a raw
integer.  It's particularly bad here because this differs from other
checksum functions (e.g. proto_ipv4_header_psum()) which take host native
lengths.

It turns out all the callers have easy access to the native endian value,
so switch it to use host order like everything else.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>