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Merged
merged 3 commits into from
May 4, 2019
Merged

Add sendmmsg syscall wrapper #2326

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9babcac
std: improve msghdr definition
daurnimator Apr 21, 2019
217b95d
std: add msghdr_const
daurnimator Apr 21, 2019
fd05675
std: add sendmmsg on linux
daurnimator Apr 21, 2019
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32 changes: 27 additions & 5 deletions std/c/freebsd.zig
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Original file line number Diff line number Diff line change
Expand Up @@ -42,14 +42,36 @@ pub const pthread_attr_t = extern struct {
};

pub const msghdr = extern struct {
msg_name: *u8,
/// optional address
msg_name: ?*sockaddr,
/// size of address
msg_namelen: socklen_t,
msg_iov: *iovec,
/// scatter/gather array
msg_iov: [*]iovec,
/// # elements in msg_iov
msg_iovlen: i32,
__pad1: i32,
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Did you remove this padding field? Doesn't that break the ABI?

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This padding field isn't present in freebsd headers. It looked like someone just copy/pasted the linux definition without checking.

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Argh. That's a problem. Now the entire freebsd.zig file needs to be audited.

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likewise netbsd.zig; which seems to have been copied from freebsd....

msg_control: *u8,
/// ancillary data
msg_control: ?*c_void,
/// ancillary data buffer len
msg_controllen: socklen_t,
__pad2: socklen_t,
/// flags on received message
msg_flags: i32,
};

pub const msghdr_const = extern struct {
/// optional address
msg_name: ?*const sockaddr,
/// size of address
msg_namelen: socklen_t,
/// scatter/gather array
msg_iov: [*]iovec_const,
/// # elements in msg_iov
msg_iovlen: i32,
/// ancillary data
msg_control: ?*c_void,
/// ancillary data buffer len
msg_controllen: socklen_t,
/// flags on received message
msg_flags: i32,
};

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32 changes: 27 additions & 5 deletions std/c/netbsd.zig
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Original file line number Diff line number Diff line change
Expand Up @@ -42,14 +42,36 @@ pub const pthread_attr_t = extern struct {
};

pub const msghdr = extern struct {
msg_name: *u8,
/// optional address
msg_name: ?*sockaddr,
/// size of address
msg_namelen: socklen_t,
msg_iov: *iovec,
/// scatter/gather array
msg_iov: [*]iovec,
/// # elements in msg_iov
msg_iovlen: i32,
__pad1: i32,
msg_control: *u8,
/// ancillary data
msg_control: ?*c_void,
/// ancillary data buffer len
msg_controllen: socklen_t,
__pad2: socklen_t,
/// flags on received message
msg_flags: i32,
};

pub const msghdr_const = extern struct {
/// optional address
msg_name: ?*const sockaddr,
/// size of address
msg_namelen: socklen_t,
/// scatter/gather array
msg_iov: [*]iovec_const,
/// # elements in msg_iov
msg_iovlen: i32,
/// ancillary data
msg_control: ?*c_void,
/// ancillary data buffer len
msg_controllen: socklen_t,
/// flags on received message
msg_flags: i32,
};

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53 changes: 52 additions & 1 deletion std/os/linux.zig
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Expand Up @@ -12,6 +12,7 @@ pub use switch (builtin.arch) {
pub use @import("linux/errno.zig");

pub const PATH_MAX = 4096;
pub const IOV_MAX = 1024;

pub const STDIN_FILENO = 0;
pub const STDOUT_FILENO = 1;
Expand Down Expand Up @@ -1193,6 +1194,16 @@ pub const iovec_const = extern struct {
iov_len: usize,
};

pub const mmsghdr = extern struct {
msg_hdr: msghdr,
msg_len: u32,
};

pub const mmsghdr_const = extern struct {
msg_hdr: msghdr_const,
msg_len: u32,
};

pub fn getsockname(fd: i32, noalias addr: *sockaddr, noalias len: *socklen_t) usize {
return syscall3(SYS_getsockname, @bitCast(usize, isize(fd)), @ptrToInt(addr), @ptrToInt(len));
}
Expand All @@ -1213,10 +1224,50 @@ pub fn getsockopt(fd: i32, level: u32, optname: u32, noalias optval: [*]u8, noal
return syscall5(SYS_getsockopt, @bitCast(usize, isize(fd)), level, optname, @ptrToInt(optval), @ptrToInt(optlen));
}

pub fn sendmsg(fd: i32, msg: *const msghdr, flags: u32) usize {
pub fn sendmsg(fd: i32, msg: *msghdr_const, flags: u32) usize {
return syscall3(SYS_sendmsg, @bitCast(usize, isize(fd)), @ptrToInt(msg), flags);
}

pub fn sendmmsg(fd: i32, msgvec: [*]mmsghdr_const, vlen: u32, flags: u32) usize {
if (@typeInfo(usize).Int.bits > @typeInfo(@typeOf(mmsghdr(undefined).msg_len)).Int.bits) {
// workaround kernel brokenness:
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I opened #2380 to address this. I'd like to resolve that issue before merging this pull request. It's not a particularly big time investment for me to do that, so I can prioritize it to unblock you.

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@daurnimator daurnimator Apr 30, 2019 •
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I'm not sure #2380 is related :P
sendmmsg is not a posix API (see my comment here)

This is an oversight in the linux kernel when introducing 64bit support to code originally written for 32bit that has now resulted in a broken kernel ABI forever.
But it does of course bring up the question of: where does this wrapper belong?

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Instead of std.os.posix mapping directly to OS-specific files, it will provide a "zig flavored POSIX" API on top of the native OS API. This is where kernel limitations will be worked around; fork might call clone on Linux, etc.

I think this applies to the sendmmsg workaround. std.os.linux.sendmmsg is meant to be completely raw. std.os.posix.sendmmsg will be a compile error on systems that don't have it, that's fine. Zig is using std.os.posix to mean a specific, slightly different thing than it means in C and that's OK.

// if adding up all iov_len overflows a i32 then split into multiple calls
// see https://www.openwall.com/lists/musl/2014/06/07/5
const kvlen = if (vlen > IOV_MAX) IOV_MAX else vlen; // matches kernel
var next_unsent: usize = 0;
for (msgvec[0..kvlen]) |*msg, i| {
var size: i32 = 0;
const msg_iovlen = @intCast(usize, msg.msg_hdr.msg_iovlen); // kernel side this is treated as unsigned
for (msg.msg_hdr.msg_iov[0..msg_iovlen]) |iov, j| {
if (iov.iov_len > std.math.maxInt(i32) or @addWithOverflow(i32, size, @intCast(i32, iov.iov_len), &size)) {
// batch-send all messages up to the current message
if (next_unsent < i) {
const batch_size = i - next_unsent;
const r = syscall4(SYS_sendmmsg, @bitCast(usize, isize(fd)), @ptrToInt(&msgvec[next_unsent]), batch_size, flags);
if (getErrno(r) != 0) return next_unsent;
if (r < batch_size) return next_unsent + r;
}
// send current message as own packet
const r = sendmsg(fd, &msg.msg_hdr, flags);
if (getErrno(r) != 0) return r;
// Linux limits the total bytes sent by sendmsg to INT_MAX, so this cast is safe.
msg.msg_len = @intCast(u32, r);
next_unsent = i + 1;
break;
}
}
}
if (next_unsent < kvlen or next_unsent == 0) { // want to make sure at least one syscall occurs (e.g. to trigger MSG_EOR)
const batch_size = kvlen - next_unsent;
const r = syscall4(SYS_sendmmsg, @bitCast(usize, isize(fd)), @ptrToInt(&msgvec[next_unsent]), batch_size, flags);
if (getErrno(r) != 0) return r;
return next_unsent + r;
}
return kvlen;
}
return syscall4(SYS_sendmmsg, @bitCast(usize, isize(fd)), @ptrToInt(msgvec), vlen, flags);
}

pub fn connect(fd: i32, addr: *const c_void, len: socklen_t) usize {
return syscall3(SYS_connect, @bitCast(usize, isize(fd)), @ptrToInt(addr), len);
}
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19 changes: 16 additions & 3 deletions std/os/linux/arm64.zig
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Expand Up @@ -2,6 +2,7 @@ const std = @import("../../std.zig");
const linux = std.os.linux;
const socklen_t = linux.socklen_t;
const iovec = linux.iovec;
const iovec_const = linux.iovec_const;

pub const SYS_io_setup = 0;
pub const SYS_io_destroy = 1;
Expand Down Expand Up @@ -415,12 +416,24 @@ pub fn syscall6(
pub extern fn clone(func: extern fn (arg: usize) u8, stack: usize, flags: u32, arg: usize, ptid: *i32, tls: usize, ctid: *i32) usize;

pub const msghdr = extern struct {
msg_name: *u8,
msg_name: ?*sockaddr,
msg_namelen: socklen_t,
msg_iov: *iovec,
msg_iov: [*]iovec,
msg_iovlen: i32,
__pad1: i32,
msg_control: *u8,
msg_control: ?*c_void,
msg_controllen: socklen_t,
__pad2: socklen_t,
msg_flags: i32,
};

pub const msghdr_const = extern struct {
msg_name: ?*const sockaddr,
msg_namelen: socklen_t,
msg_iov: [*]iovec_const,
msg_iovlen: i32,
__pad1: i32,
msg_control: ?*c_void,
msg_controllen: socklen_t,
__pad2: socklen_t,
msg_flags: i32,
Expand Down
20 changes: 17 additions & 3 deletions std/os/linux/x86_64.zig
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@@ -1,7 +1,9 @@
const std = @import("../../std.zig");
const linux = std.os.linux;
const sockaddr = linux.sockaddr;
const socklen_t = linux.socklen_t;
const iovec = linux.iovec;
const iovec_const = linux.iovec_const;

pub const SYS_read = 0;
pub const SYS_write = 1;
Expand Down Expand Up @@ -483,12 +485,24 @@ pub nakedcc fn restore_rt() void {
}

pub const msghdr = extern struct {
msg_name: *u8,
msg_name: ?*sockaddr,
msg_namelen: socklen_t,
msg_iov: *iovec,
msg_iov: [*]iovec,
msg_iovlen: i32,
__pad1: i32,
msg_control: *u8,
msg_control: ?*c_void,
msg_controllen: socklen_t,
__pad2: socklen_t,
msg_flags: i32,
};

pub const msghdr_const = extern struct {
msg_name: ?*const sockaddr,
msg_namelen: socklen_t,
msg_iov: [*]iovec_const,
msg_iovlen: i32,
__pad1: i32,
msg_control: ?*c_void,
msg_controllen: socklen_t,
__pad2: socklen_t,
msg_flags: i32,
Expand Down