MDEV-15655: Add Linux abstract socket support
The functionality of the socket system variable is extended
here such that a preciding '@' indicates that the socket
will be an abstract socket. Thie socket name wil be
the remainder of the name after the '@'. This is consistent
with the approached used by systemd in socket activation.
Thanks to Sergey Vojtovich:
On OS X sockaddr_un is defined as:
struct sockaddr_un
{
u_char sun_len;
u_char sun_family;
char sun_path[104];
};
There is a comment in man 7 unix (on linux):
"
On Linux, the above offsetof() expression equates to the same value as sizeof(sa_family_t),
but some other implementations include other fields before sun_path, so the offsetof()
expression more portably describes the size of the address structure.
"
As such, use the offsetof for Linux and use the previous sizeof(UNIXaddr)
for non-unix platforms as that's what worked before and they don't
support abstract sockets so there's no compatibility problem..
strace -fe trace=networking mysqld --skip-networking --socket @abc ...
...
[pid 10578] socket(AF_UNIX, SOCK_STREAM|SOCK_CLOEXEC, 0) = 22
[pid 10578] setsockopt(22, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
[pid 10578] bind(22, {sa_family=AF_UNIX, sun_path=@"abc"}, 6) = 0
[pid 10578] listen(22, 80) = 0
...
Version: '10.3.6-MariaDB-log' socket: '@abc' port: 0 Source distribution
$ lsof -p 10578
mysqld 10578 dan 22u unix 0x00000000087e688c 0t0 4787815 @abc type=STREAM
2018-03-25 04:42:48 +02:00
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select 1;
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