# This is a fork of the (for now) unmaintained Sys::Syscall 0.25,
# specifically the Debian libsys-syscall-perl 0.25-6 version to
# fix upstream regressions in 0.25.
#
# See devel/syscall-list in the public-inbox source tree for maintenance
# <https://80x24.org/public-inbox.git>, and machines from the GCC Farm:
# <https://cfarm.tetaneutral.net/>
#
# This license differs from the rest of public-inbox
#
# This module is Copyright (c) 2005 Six Apart, Ltd.
# Copyright (C) all contributors <meta@public-inbox.org>
#
# All rights reserved.
#
# You may distribute under the terms of either the GNU General Public
# License or the Artistic License, as specified in the Perl README file.
package PublicInbox::Syscall;
use v5.12;
use parent qw(Exporter);
use POSIX qw(ENOENT ENOSYS EINVAL O_NONBLOCK);
use Socket qw(SOL_SOCKET SCM_RIGHTS);
use Config;

# $VERSION = '0.25'; # Sys::Syscall version
our @EXPORT_OK = qw(epoll_ctl epoll_create epoll_wait
                  EPOLLIN EPOLLOUT EPOLLET
                  EPOLL_CTL_ADD EPOLL_CTL_DEL EPOLL_CTL_MOD
                  EPOLLONESHOT EPOLLEXCLUSIVE
                  signalfd rename_noreplace);
our %EXPORT_TAGS = (epoll => [qw(epoll_ctl epoll_create epoll_wait
                             EPOLLIN EPOLLOUT
                             EPOLL_CTL_ADD EPOLL_CTL_DEL EPOLL_CTL_MOD
                             EPOLLONESHOT EPOLLEXCLUSIVE)],
                );

use constant {
	EPOLLIN => 1,
	EPOLLOUT => 4,
	# EPOLLERR => 8,
	# EPOLLHUP => 16,
	# EPOLLRDBAND => 128,
	EPOLLEXCLUSIVE => (1 << 28),
	EPOLLONESHOT => (1 << 30),
	EPOLLET => (1 << 31),
	EPOLL_CTL_ADD => 1,
	EPOLL_CTL_DEL => 2,
	EPOLL_CTL_MOD => 3,
	SIZEOF_int => $Config{intsize},
	SIZEOF_size_t => $Config{sizesize},
	NUL => "\0",
};

use constant {
	TMPL_size_t => SIZEOF_size_t == 8 ? 'Q' : 'L',
	BYTES_4_hole => SIZEOF_size_t == 8 ? 'L' : '',
	# cmsg_len, cmsg_level, cmsg_type
	SIZEOF_cmsghdr => SIZEOF_int * 2 + SIZEOF_size_t,
};

my @BYTES_4_hole = BYTES_4_hole ? (0) : ();
our $loaded_syscall = 0;

sub _load_syscall {
    # props to Gaal for this!
    return if $loaded_syscall++;
    my $clean = sub {
        delete @INC{qw<syscall.ph asm/unistd.ph bits/syscall.ph
                        _h2ph_pre.ph sys/syscall.ph>};
    };
    $clean->(); # don't trust modules before us
    my $rv = eval { require 'syscall.ph'; 1 } || eval { require 'sys/syscall.ph'; 1 };
    $clean->(); # don't require modules after us trust us
    $rv;
}


our (
     $SYS_epoll_create,
     $SYS_epoll_ctl,
     $SYS_epoll_wait,
     $SYS_signalfd4,
     $SYS_renameat2,
     );

my ($SYS_sendmsg, $SYS_recvmsg);
my $SYS_fstatfs; # don't need fstatfs64, just statfs.f_type
my ($FS_IOC_GETFLAGS, $FS_IOC_SETFLAGS);
my $SFD_CLOEXEC = 02000000; # Perl does not expose O_CLOEXEC
our $no_deprecated = 0;

if ($^O eq "linux") {
    my (undef, undef, $release, undef, $machine) = POSIX::uname();
    my ($maj, $min) = ($release =~ /\A([0-9]+)\.([0-9]+)/);
    $SYS_renameat2 = 0 if "$maj.$min" < 3.15;
    # whether the machine requires 64-bit numbers to be on 8-byte
    # boundaries.
    my $u64_mod_8 = 0;

    # if we're running on an x86_64 kernel, but a 32-bit process,
    # we need to use the x32 or i386 syscall numbers.
    if ($machine eq "x86_64" && $Config{ptrsize} == 4) {
        $machine = $Config{cppsymbols} =~ /\b__ILP32__=1\b/ ? 'x32' : 'i386';
    }

    # Similarly for mips64 vs mips
    if ($machine eq "mips64" && $Config{ptrsize} == 4) {
        $machine = "mips";
    }

    if ($machine =~ m/^i[3456]86$/) {
        $SYS_epoll_create = 254;
        $SYS_epoll_ctl    = 255;
        $SYS_epoll_wait   = 256;
        $SYS_signalfd4 = 327;
        $SYS_renameat2 //= 353;
	$SYS_fstatfs = 100;
	$SYS_sendmsg = 370;
	$SYS_recvmsg = 372;
	$FS_IOC_GETFLAGS = 0x80046601;
	$FS_IOC_SETFLAGS = 0x40046602;
    } elsif ($machine eq "x86_64") {
        $SYS_epoll_create = 213;
        $SYS_epoll_ctl    = 233;
        $SYS_epoll_wait   = 232;
        $SYS_signalfd4 = 289;
	$SYS_renameat2 //= 316;
	$SYS_fstatfs = 138;
	$SYS_sendmsg = 46;
	$SYS_recvmsg = 47;
	$FS_IOC_GETFLAGS = 0x80086601;
	$FS_IOC_SETFLAGS = 0x40086602;
    } elsif ($machine eq 'x32') {
        $SYS_epoll_create = 1073742037;
        $SYS_epoll_ctl = 1073742057;
        $SYS_epoll_wait = 1073742056;
        $SYS_signalfd4 = 1073742113;
	$SYS_renameat2 //= 0x40000000 + 316;
	$SYS_fstatfs = 138;
	$SYS_sendmsg = 0x40000206;
	$SYS_recvmsg = 0x40000207;
	$FS_IOC_GETFLAGS = 0x80046601;
	$FS_IOC_SETFLAGS = 0x40046602;
    } elsif ($machine eq 'sparc64') {
	$SYS_epoll_create = 193;
	$SYS_epoll_ctl = 194;
	$SYS_epoll_wait = 195;
	$u64_mod_8 = 1;
	$SYS_signalfd4 = 317;
	$SYS_renameat2 //= 345;
	$SFD_CLOEXEC = 020000000;
	$SYS_fstatfs = 158;
	$SYS_sendmsg = 114;
	$SYS_recvmsg = 113;
	$FS_IOC_GETFLAGS = 0x40086601;
	$FS_IOC_SETFLAGS = 0x80086602;
    } elsif ($machine =~ m/^parisc/) {
        $SYS_epoll_create = 224;
        $SYS_epoll_ctl    = 225;
        $SYS_epoll_wait   = 226;
        $u64_mod_8        = 1;
        $SYS_signalfd4 = 309;
    } elsif ($machine =~ m/^ppc64/) {
        $SYS_epoll_create = 236;
        $SYS_epoll_ctl    = 237;
        $SYS_epoll_wait   = 238;
        $u64_mod_8        = 1;
        $SYS_signalfd4 = 313;
	$SYS_renameat2 //= 357;
	$SYS_fstatfs = 100;
	$SYS_sendmsg = 341;
	$SYS_recvmsg = 342;
	$FS_IOC_GETFLAGS = 0x40086601;
	$FS_IOC_SETFLAGS = 0x80086602;
    } elsif ($machine eq "ppc") {
        $SYS_epoll_create = 236;
        $SYS_epoll_ctl    = 237;
        $SYS_epoll_wait   = 238;
        $u64_mod_8        = 1;
        $SYS_signalfd4 = 313;
	$SYS_renameat2 //= 357;
	$SYS_fstatfs = 100;
	$FS_IOC_GETFLAGS = 0x40086601;
	$FS_IOC_SETFLAGS = 0x80086602;
    } elsif ($machine =~ m/^s390/) { # untested, no machine on cfarm
        $SYS_epoll_create = 249;
        $SYS_epoll_ctl    = 250;
        $SYS_epoll_wait   = 251;
        $u64_mod_8        = 1;
        $SYS_signalfd4 = 322;
	$SYS_renameat2 //= 347;
	$SYS_fstatfs = 100;
	$SYS_sendmsg = 370;
	$SYS_recvmsg = 372;
    } elsif ($machine eq 'ia64') { # untested, no machine on cfarm
        $SYS_epoll_create = 1243;
        $SYS_epoll_ctl    = 1244;
        $SYS_epoll_wait   = 1245;
        $u64_mod_8        = 1;
        $SYS_signalfd4 = 289;
    } elsif ($machine eq "alpha") { # untested, no machine on cfarm
        # natural alignment, ints are 32-bits
        $SYS_epoll_create = 407;
        $SYS_epoll_ctl    = 408;
        $SYS_epoll_wait   = 409;
        $u64_mod_8        = 1;
        $SYS_signalfd4 = 484;
	$SFD_CLOEXEC = 010000000;
    } elsif ($machine =~ /\A(?:loong)?aarch64\z/ || $machine eq 'riscv64') {
        $SYS_epoll_create = 20;  # (sys_epoll_create1)
        $SYS_epoll_ctl    = 21;
        $SYS_epoll_wait   = 22;  # (sys_epoll_pwait)
        $u64_mod_8        = 1;
        $no_deprecated    = 1;
        $SYS_signalfd4 = 74;
	$SYS_renameat2 //= 276;
	$SYS_fstatfs = 44;
	$SYS_sendmsg = 211;
	$SYS_recvmsg = 212;
	$FS_IOC_GETFLAGS = 0x80086601;
	$FS_IOC_SETFLAGS = 0x40086602;
    } elsif ($machine =~ m/arm(v\d+)?.*l/) { # ARM OABI (untested on cfarm)
        $SYS_epoll_create = 250;
        $SYS_epoll_ctl    = 251;
        $SYS_epoll_wait   = 252;
        $u64_mod_8        = 1;
        $SYS_signalfd4 = 355;
	$SYS_renameat2 //= 382;
	$SYS_fstatfs = 100;
	$SYS_sendmsg = 296;
	$SYS_recvmsg = 297;
    } elsif ($machine =~ m/^mips64/) { # cfarm only has 32-bit userspace
        $SYS_epoll_create = 5207;
        $SYS_epoll_ctl    = 5208;
        $SYS_epoll_wait   = 5209;
        $u64_mod_8        = 1;
        $SYS_signalfd4 = 5283;
	$SYS_renameat2 //= 5311;
	$SYS_fstatfs = 5135;
	$SYS_sendmsg = 5045;
	$SYS_recvmsg = 5046;
	$FS_IOC_GETFLAGS = 0x40046601;
	$FS_IOC_SETFLAGS = 0x80046602;
    } elsif ($machine =~ m/^mips/) { # 32-bit, tested on mips64 cfarm machine
        $SYS_epoll_create = 4248;
        $SYS_epoll_ctl    = 4249;
        $SYS_epoll_wait   = 4250;
        $u64_mod_8        = 1;
        $SYS_signalfd4 = 4324;
	$SYS_renameat2 //= 4351;
	$SYS_fstatfs = 4100;
	$SYS_sendmsg = 4179;
	$SYS_recvmsg = 4177;
	$FS_IOC_GETFLAGS = 0x40046601;
	$FS_IOC_SETFLAGS = 0x80046602;
    } else {
        # as a last resort, try using the *.ph files which may not
        # exist or may be wrong
        _load_syscall();
        $SYS_epoll_create = eval { &SYS_epoll_create; } || 0;
        $SYS_epoll_ctl    = eval { &SYS_epoll_ctl;    } || 0;
        $SYS_epoll_wait   = eval { &SYS_epoll_wait;   } || 0;

	# Note: do NOT add new syscalls to depend on *.ph, here.
	# Better to miss syscalls (so we can fallback to IO::Poll)
	# than to use wrong ones, since the names are not stable
	# (at least not on FreeBSD), if the actual numbers are.
    }

    if ($u64_mod_8) {
        *epoll_wait = \&epoll_wait_mod8;
        *epoll_ctl = \&epoll_ctl_mod8;
    } else {
        *epoll_wait = \&epoll_wait_mod4;
        *epoll_ctl = \&epoll_ctl_mod4;
    }
}
# use Inline::C for *BSD-only or general POSIX stuff.
# Linux guarantees stable syscall numbering, BSDs only offer a stable libc
# use scripts/syscall-list on Linux to detect new syscall numbers

############################################################################
# epoll functions
############################################################################

sub epoll_defined { $SYS_epoll_create ? 1 : 0; }

sub epoll_create {
	syscall($SYS_epoll_create, $no_deprecated ? 0 : 100);
}

# epoll_ctl wrapper
# ARGS: (epfd, op, fd, events_mask)
sub epoll_ctl_mod4 {
    syscall($SYS_epoll_ctl, $_[0]+0, $_[1]+0, $_[2]+0, pack("LLL", $_[3], $_[2], 0));
}
sub epoll_ctl_mod8 {
    syscall($SYS_epoll_ctl, $_[0]+0, $_[1]+0, $_[2]+0, pack("LLLL", $_[3], 0, $_[2], 0));
}

# epoll_wait wrapper
# ARGS: (epfd, maxevents, timeout (milliseconds), arrayref)
#  arrayref: values modified to be [$fd, $event]
our $epoll_wait_events = '';
our $epoll_wait_size = 0;
sub epoll_wait_mod4 {
	my ($epfd, $maxevents, $timeout_msec, $events) = @_;
	# resize our static buffer if maxevents bigger than we've ever done
	if ($maxevents > $epoll_wait_size) {
		$epoll_wait_size = $maxevents;
		vec($epoll_wait_events, $maxevents * 12 * 8 - 1, 1) = 0;
	}
	@$events = ();
	my $ct = syscall($SYS_epoll_wait, $epfd, $epoll_wait_events,
			$maxevents, $timeout_msec);
	for (0..$ct - 1) {
		# 12-byte struct epoll_event
		# 4 bytes uint32_t events mask (skipped, useless to us)
		# 8 bytes: epoll_data_t union (first 4 bytes are the fd)
		# So we skip the first 4 bytes and take the middle 4:
		$events->[$_] = unpack('L', substr($epoll_wait_events,
							12 * $_ + 4, 4));
	}
}

sub epoll_wait_mod8 {
	my ($epfd, $maxevents, $timeout_msec, $events) = @_;

	# resize our static buffer if maxevents bigger than we've ever done
	if ($maxevents > $epoll_wait_size) {
		$epoll_wait_size = $maxevents;
		vec($epoll_wait_events, $maxevents * 16 * 8 - 1, 1) = 0;
	}
	@$events = ();
	my $ct = syscall($SYS_epoll_wait, $epfd, $epoll_wait_events,
			$maxevents, $timeout_msec,
			$no_deprecated ? undef : ());
	for (0..$ct - 1) {
		# 16-byte struct epoll_event
		# 4 bytes uint32_t events mask (skipped, useless to us)
		# 4 bytes padding (skipped, useless)
		# 8 bytes epoll_data_t union (first 4 bytes are the fd)
		# So skip the first 8 bytes, take 4, and ignore the last 4:
		$events->[$_] = unpack('L', substr($epoll_wait_events,
							16 * $_ + 8, 4));
	}
}

sub signalfd ($$) {
	my ($signos, $nonblock) = @_;
	if ($SYS_signalfd4) {
		my $set = POSIX::SigSet->new(@$signos);
		syscall($SYS_signalfd4, -1, "$$set",
			# $Config{sig_count} is NSIG, so this is NSIG/8:
			int($Config{sig_count}/8),
			# SFD_NONBLOCK == O_NONBLOCK for every architecture
			($nonblock ? O_NONBLOCK : 0) |$SFD_CLOEXEC);
	} else {
		$! = ENOSYS;
		undef;
	}
}

sub _rename_noreplace_racy ($$) {
	my ($old, $new) = @_;
	if (link($old, $new)) {
		warn "unlink $old: $!\n" if !unlink($old) && $! != ENOENT;
		1
	} else {
		undef;
	}
}

# TODO: support FD args?
sub rename_noreplace ($$) {
	my ($old, $new) = @_;
	if ($SYS_renameat2) { # RENAME_NOREPLACE = 1, AT_FDCWD = -100
		my $ret = syscall($SYS_renameat2, -100, $old, -100, $new, 1);
		if ($ret == 0) {
			1; # like rename() perlop
		} elsif ($! == ENOSYS || $! == EINVAL) {
			undef $SYS_renameat2;
			_rename_noreplace_racy($old, $new);
		} else {
			undef
		}
	} else {
		_rename_noreplace_racy($old, $new);
	}
}

sub nodatacow_fh ($) {
	my ($fh) = @_;
	my $buf = "\0" x 120;
	syscall($SYS_fstatfs // return, fileno($fh), $buf) == 0 or
		return warn("fstatfs: $!\n");
	my $f_type = unpack('l!', $buf); # statfs.f_type is a signed word
	return if $f_type != 0x9123683E; # BTRFS_SUPER_MAGIC

	$FS_IOC_GETFLAGS //
		return warn('FS_IOC_GETFLAGS undefined for platform');
	ioctl($fh, $FS_IOC_GETFLAGS, $buf) //
		return warn("FS_IOC_GETFLAGS: $!\n");
	my $attr = unpack('l!', $buf);
	return if ($attr & 0x00800000); # FS_NOCOW_FL;
	ioctl($fh, $FS_IOC_SETFLAGS, pack('l', $attr | 0x00800000)) //
		warn("FS_IOC_SETFLAGS: $!\n");
}

sub nodatacow_dir {
	if (open my $fh, '<', $_[0]) { nodatacow_fh($fh) }
}

sub CMSG_ALIGN ($) { ($_[0] + SIZEOF_size_t - 1) & ~(SIZEOF_size_t - 1) }
use constant CMSG_ALIGN_SIZEOF_cmsghdr => CMSG_ALIGN(SIZEOF_cmsghdr);
sub CMSG_SPACE ($) { CMSG_ALIGN($_[0]) + CMSG_ALIGN_SIZEOF_cmsghdr }
sub CMSG_LEN ($) { CMSG_ALIGN_SIZEOF_cmsghdr + $_[0] }
use constant msg_controllen => CMSG_SPACE(10 * SIZEOF_int) + 16; # 10 FDs

if (defined($SYS_sendmsg) && defined($SYS_recvmsg)) {
no warnings 'once';
*send_cmd4 = sub ($$$$) {
	my ($sock, $fds, undef, $flags) = @_;
	my $iov = pack('P'.TMPL_size_t,
			$_[2] // NUL, length($_[2] // NUL) || 1);
	my $cmsghdr = pack(TMPL_size_t . # cmsg_len
			'LL' .  # cmsg_level, cmsg_type,
			('i' x scalar(@$fds)),
			CMSG_LEN(scalar(@$fds) * SIZEOF_int), # cmsg_len
			SOL_SOCKET, SCM_RIGHTS, # cmsg_{level,type}
			@$fds); # CMSG_DATA
	my $mh = pack('PL' . # msg_name, msg_namelen (socklen_t (U32))
			BYTES_4_hole . # 4-byte padding on 64-bit
			'P'.TMPL_size_t . # msg_iov, msg_iovlen,
			'P'.TMPL_size_t . # msg_control, msg_controllen,
			'i', # msg_flags
			NUL, 0, # msg_name, msg_namelen (unused)
			@BYTES_4_hole,
			$iov, 1, # msg_iov, msg_iovlen
			$cmsghdr, # msg_control
			CMSG_SPACE(scalar(@$fds) * SIZEOF_int), # msg_controllen
			0); # msg_flags
	my $sent;
	my $try = 0;
	do {
		$sent = syscall($SYS_sendmsg, fileno($sock), $mh, $flags);
	} while ($sent < 0 &&
			($!{ENOBUFS} || $!{ENOMEM} || $!{ETOOMANYREFS}) &&
			(++$try < 50) &&
			warn "sleeping on sendmsg: $! (#$try)\n" &&
			select(undef, undef, undef, 0.1) == 0);
	$sent >= 0 ? $sent : undef;
};

*recv_cmd4 = sub ($$$) {
	my ($sock, undef, $len) = @_;
	vec($_[1], ($len + 1) * 8, 1) = 0;
	my $cmsghdr = "\0" x msg_controllen; # 10 * sizeof(int)
	my $iov = pack('P'.TMPL_size_t, $_[1], $len);
	my $mh = pack('PL' . # msg_name, msg_namelen (socklen_t (U32))
			BYTES_4_hole . # 4-byte padding on 64-bit
			'P'.TMPL_size_t . # msg_iov, msg_iovlen,
			'P'.TMPL_size_t . # msg_control, msg_controllen,
			'i', # msg_flags
			NUL, 0, # msg_name, msg_namelen (unused)
			@BYTES_4_hole,
			$iov, 1, # msg_iov, msg_iovlen
			$cmsghdr, # msg_control
			msg_controllen,
			0); # msg_flags
	my $r = syscall($SYS_recvmsg, fileno($sock), $mh, 0);
	return (undef) if $r < 0; # $! set
	substr($_[1], $r, length($_[1]), '');
	my @ret;
	if ($r > 0) {
		my ($len, $lvl, $type, @fds) = unpack(TMPL_size_t . # cmsg_len
					'LLi*', # cmsg_level, cmsg_type, @fds
					$cmsghdr);
		if ($lvl == SOL_SOCKET && $type == SCM_RIGHTS) {
			$len -= CMSG_ALIGN_SIZEOF_cmsghdr;
			@ret = @fds[0..(($len / SIZEOF_int) - 1)];
		}
	}
	@ret;
};
}

1;

=head1 WARRANTY

This is free software. IT COMES WITHOUT WARRANTY OF ANY KIND.

=head1 AUTHORS

Brad Fitzpatrick <brad@danga.com>