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-rw-r--r--MANIFEST1
-rwxr-xr-xdevel/syscall-list10
-rw-r--r--lib/PublicInbox/IMAPTracker.pm6
-rw-r--r--lib/PublicInbox/LeiMailSync.pm6
-rw-r--r--lib/PublicInbox/MiscIdx.pm6
-rw-r--r--lib/PublicInbox/Msgmap.pm6
-rw-r--r--lib/PublicInbox/NDC_PP.pm34
-rw-r--r--lib/PublicInbox/Over.pm7
-rw-r--r--lib/PublicInbox/SearchIdx.pm7
-rw-r--r--lib/PublicInbox/SharedKV.pm6
-rw-r--r--lib/PublicInbox/Spawn.pm76
-rw-r--r--lib/PublicInbox/Syscall.pm46
-rw-r--r--lib/PublicInbox/Xapcmd.pm11
-rw-r--r--t/nodatacow.t36
14 files changed, 102 insertions, 156 deletions
diff --git a/MANIFEST b/MANIFEST
index 1287182d..ca840210 100644
--- a/MANIFEST
+++ b/MANIFEST
@@ -289,7 +289,6 @@ lib/PublicInbox/MsgIter.pm
 lib/PublicInbox/MsgTime.pm
 lib/PublicInbox/Msgmap.pm
 lib/PublicInbox/MultiGit.pm
-lib/PublicInbox/NDC_PP.pm
 lib/PublicInbox/NNTP.pm
 lib/PublicInbox/NNTPD.pm
 lib/PublicInbox/NNTPdeflate.pm
diff --git a/devel/syscall-list b/devel/syscall-list
index 3d55df1f..a6b1bfa7 100755
--- a/devel/syscall-list
+++ b/devel/syscall-list
@@ -26,8 +26,10 @@ system($cc, '-o', $x, $f, @cflags) == 0 or die "cc failed \$?=$?";
 exec($x);
 __DATA__
 #define _GNU_SOURCE
-#include <unistd.h>
 #include <sys/syscall.h>
+#include <sys/ioctl.h>
+#include <linux/fs.h>
+#include <unistd.h>
 #include <stdio.h>
 
 #define D(x) printf("$" #x " = %ld;\n", (long)x)
@@ -46,6 +48,12 @@ int main(void)
         D(SYS_inotify_add_watch);
         D(SYS_inotify_rm_watch);
         D(SYS_prctl);
+        D(SYS_fstatfs);
+#ifdef FS_IOC_GETFLAGS
+        printf("FS_IOC_GETFLAGS=%#lx\nFS_IOC_SETFLAGS=%#lx\n",
+                (unsigned long)FS_IOC_GETFLAGS, (unsigned long)FS_IOC_SETFLAGS);
+#endif
+
 #ifdef SYS_renameat2
         D(SYS_renameat2);
 #endif
diff --git a/lib/PublicInbox/IMAPTracker.pm b/lib/PublicInbox/IMAPTracker.pm
index 2fd66440..4efa8a7e 100644
--- a/lib/PublicInbox/IMAPTracker.pm
+++ b/lib/PublicInbox/IMAPTracker.pm
@@ -1,4 +1,4 @@
-# Copyright (C) 2018-2021 all contributors <meta@public-inbox.org>
+# Copyright (C) all contributors <meta@public-inbox.org>
 # License: AGPL-3.0+ <https://www.gnu.org/licenses/agpl-3.0.txt>
 package PublicInbox::IMAPTracker;
 use strict;
@@ -75,11 +75,11 @@ sub new {
         }
         if (!-f $dbname) {
                 require File::Path;
-                require PublicInbox::Spawn;
+                require PublicInbox::Syscall;
                 my ($dir) = ($dbname =~ m!(.*?/)[^/]+\z!);
                 File::Path::mkpath($dir);
+                PublicInbox::Syscall::nodatacow_dir($dir);
                 open my $fh, '+>>', $dbname or die "failed to open $dbname: $!";
-                PublicInbox::Spawn::nodatacow_fd(fileno($fh));
         }
         my $self = bless { lock_path => "$dbname.lock", url => $url }, $class;
         $self->lock_acquire;
diff --git a/lib/PublicInbox/LeiMailSync.pm b/lib/PublicInbox/LeiMailSync.pm
index 124eb969..182b0c22 100644
--- a/lib/PublicInbox/LeiMailSync.pm
+++ b/lib/PublicInbox/LeiMailSync.pm
@@ -1,4 +1,4 @@
-# Copyright (C) 2021 all contributors <meta@public-inbox.org>
+# Copyright (C) all contributors <meta@public-inbox.org>
 # License: AGPL-3.0+ <https://www.gnu.org/licenses/agpl-3.0.txt>
 
 # for maintaining synchronization between lei/store <=> Maildir|MH|IMAP|JMAP
@@ -15,9 +15,9 @@ sub dbh_new {
         my $f = $self->{filename};
         my $creat = $rw && !-s $f;
         if ($creat) {
-                require PublicInbox::Spawn;
+                require PublicInbox::Syscall;
                 open my $fh, '+>>', $f or Carp::croak "open($f): $!";
-                PublicInbox::Spawn::nodatacow_fd(fileno($fh));
+                PublicInbox::Syscall::nodatacow_fh($fh);
         }
         my $dbh = DBI->connect("dbi:SQLite:dbname=$f",'','', {
                 AutoCommit => 1,
diff --git a/lib/PublicInbox/MiscIdx.pm b/lib/PublicInbox/MiscIdx.pm
index f5a374b2..dc15442d 100644
--- a/lib/PublicInbox/MiscIdx.pm
+++ b/lib/PublicInbox/MiscIdx.pm
@@ -1,4 +1,4 @@
-# Copyright (C) 2020-2021 all contributors <meta@public-inbox.org>
+# Copyright (C) all contributors <meta@public-inbox.org>
 # License: AGPL-3.0+ <https://www.gnu.org/licenses/agpl-3.0.txt>
 
 # like PublicInbox::SearchIdx, but for searching for non-mail messages.
@@ -16,11 +16,11 @@ use v5.10.1;
 use PublicInbox::InboxWritable;
 use PublicInbox::Search; # for SWIG Xapian and Search::Xapian compat
 use PublicInbox::SearchIdx qw(index_text term_generator add_val);
-use PublicInbox::Spawn qw(nodatacow_dir);
 use Carp qw(croak);
 use File::Path ();
 use PublicInbox::MiscSearch;
 use PublicInbox::Config;
+use PublicInbox::Syscall;
 my $json;
 
 sub new {
@@ -28,7 +28,7 @@ sub new {
         PublicInbox::SearchIdx::load_xapian_writable();
         my $mi_dir = "$eidx->{xpfx}/misc";
         File::Path::mkpath($mi_dir);
-        nodatacow_dir($mi_dir);
+        PublicInbox::Syscall::nodatacow_dir($mi_dir);
         my $flags = $PublicInbox::SearchIdx::DB_CREATE_OR_OPEN;
         $flags |= $PublicInbox::SearchIdx::DB_NO_SYNC if $eidx->{-no_fsync};
         $json //= PublicInbox::Config::json();
diff --git a/lib/PublicInbox/Msgmap.pm b/lib/PublicInbox/Msgmap.pm
index 699a8bf0..1041cd17 100644
--- a/lib/PublicInbox/Msgmap.pm
+++ b/lib/PublicInbox/Msgmap.pm
@@ -1,4 +1,4 @@
-# Copyright (C) 2015-2021 all contributors <meta@public-inbox.org>
+# Copyright (C) all contributors <meta@public-inbox.org>
 # License: AGPL-3.0+ <https://www.gnu.org/licenses/agpl-3.0.txt>
 
 # bidirectional Message-ID <-> Article Number mapping for the NNTP
@@ -13,7 +13,6 @@ use v5.10.1;
 use DBI;
 use DBD::SQLite;
 use PublicInbox::Over;
-use PublicInbox::Spawn;
 use Scalar::Util qw(blessed);
 
 sub new_file {
@@ -53,7 +52,8 @@ sub tmp_clone {
         require File::Temp;
         my $tmp = "mm_tmp-$$-XXXX";
         my ($fh, $fn) = File::Temp::tempfile($tmp, EXLOCK => 0, DIR => $dir);
-        PublicInbox::Spawn::nodatacow_fd(fileno($fh));
+        require PublicInbox::Syscall;
+        PublicInbox::Syscall::nodatacow_fh($fh);
         $self->{dbh}->sqlite_backup_to_file($fn);
         $tmp = ref($self)->new_file($fn, 2);
         $tmp->{dbh}->do('PRAGMA journal_mode = MEMORY');
diff --git a/lib/PublicInbox/NDC_PP.pm b/lib/PublicInbox/NDC_PP.pm
deleted file mode 100644
index 57abccbe..00000000
--- a/lib/PublicInbox/NDC_PP.pm
+++ /dev/null
@@ -1,34 +0,0 @@
-# Copyright (C) 2020-2021 all contributors <meta@public-inbox.org>
-# License: AGPL-3.0+ <https://www.gnu.org/licenses/agpl-3.0.txt>
-
-# Pure-perl class for Linux non-Inline::C users to disable COW for btrfs
-package PublicInbox::NDC_PP;
-use strict;
-use v5.10.1;
-
-sub nodatacow_dir ($) {
-        my ($path) = @_;
-        open my $mh, '<', '/proc/self/mounts' or return;
-        for (grep(/ btrfs /, <$mh>)) {
-                my (undef, $mnt_path, $type) = split(/ /);
-                next if $type ne 'btrfs'; # in case of false-positive from grep
-
-                # weird chars are escaped as octal
-                $mnt_path =~ s/\\(0[0-9]{2})/chr(oct($1))/egs;
-                $mnt_path .= '/' unless $mnt_path =~ m!/\z!;
-                if (index($path, $mnt_path) == 0) {
-                        # error goes to stderr, but non-fatal for us
-                        system('chattr', '+C', $path);
-                        last;
-                }
-        }
-}
-
-sub nodatacow_fd ($) {
-        my ($fd) = @_;
-        return if $^O ne 'linux';
-        defined(my $path = readlink("/proc/self/fd/$fd")) or return;
-        nodatacow_dir($path);
-}
-
-1;
diff --git a/lib/PublicInbox/Over.pm b/lib/PublicInbox/Over.pm
index 30ad949d..786f9d92 100644
--- a/lib/PublicInbox/Over.pm
+++ b/lib/PublicInbox/Over.pm
@@ -1,4 +1,4 @@
-# Copyright (C) 2018-2021 all contributors <meta@public-inbox.org>
+# Copyright (C) all contributors <meta@public-inbox.org>
 # License: AGPL-3.0+ <https://www.gnu.org/licenses/agpl-3.0.txt>
 
 # for XOVER, OVER in NNTP, and feeds/homepage/threads in PSGI
@@ -18,11 +18,10 @@ sub dbh_new {
         my $f = delete $self->{filename};
         if (!-s $f) { # SQLite defaults mode to 0644, we want 0666
                 if ($rw) {
-                        require PublicInbox::Spawn;
+                        require PublicInbox::Syscall;
                         my ($dir) = ($f =~ m!(.+)/[^/]+\z!);
-                        PublicInbox::Spawn::nodatacow_dir($dir);
+                        PublicInbox::Syscall::nodatacow_dir($dir);
                         open my $fh, '+>>', $f or die "failed to open $f: $!";
-                        PublicInbox::Spawn::nodatacow_fd(fileno($fh));
                 } else {
                         $self->{filename} = $f; # die on stat() below:
                 }
diff --git a/lib/PublicInbox/SearchIdx.pm b/lib/PublicInbox/SearchIdx.pm
index 4e5d7d44..95b14c3a 100644
--- a/lib/PublicInbox/SearchIdx.pm
+++ b/lib/PublicInbox/SearchIdx.pm
@@ -1,4 +1,4 @@
-# Copyright (C) 2015-2021 all contributors <meta@public-inbox.org>
+# Copyright (C) all contributors <meta@public-inbox.org>
 # License: AGPL-3.0+ <https://www.gnu.org/licenses/agpl-3.0.txt>
 # based on notmuch, but with no concept of folders, files
 #
@@ -20,7 +20,7 @@ use Carp qw(croak carp);
 use POSIX qw(strftime);
 use Time::Local qw(timegm);
 use PublicInbox::OverIdx;
-use PublicInbox::Spawn qw(spawn nodatacow_dir);
+use PublicInbox::Spawn qw(spawn);
 use PublicInbox::Git qw(git_unquote);
 use PublicInbox::MsgTime qw(msg_timestamp msg_datestamp);
 use PublicInbox::Address;
@@ -139,7 +139,8 @@ sub idx_acquire {
                 if (!-d $dir && (!$is_shard ||
                                 ($is_shard && need_xapian($self)))) {
                         File::Path::mkpath($dir);
-                        nodatacow_dir($dir);
+                        require PublicInbox::Syscall;
+                        PublicInbox::Syscall::nodatacow_dir($dir);
                         $self->{-set_has_threadid_once} = 1;
                 }
         }
diff --git a/lib/PublicInbox/SharedKV.pm b/lib/PublicInbox/SharedKV.pm
index 4297efed..95a3cb14 100644
--- a/lib/PublicInbox/SharedKV.pm
+++ b/lib/PublicInbox/SharedKV.pm
@@ -1,4 +1,4 @@
-# Copyright (C) 2020-2021 all contributors <meta@public-inbox.org>
+# Copyright (C) all contributors <meta@public-inbox.org>
 # License: AGPL-3.0+ <https://www.gnu.org/licenses/agpl-3.0.txt>
 
 # fork()-friendly key-value store.  Will be used for making
@@ -49,9 +49,9 @@ sub new {
         my $f = $self->{filename} = "$dir/$base.sqlite3";
         $self->{lock_path} = $opt->{lock_path} // "$dir/$base.flock";
         unless (-s $f) {
-                PublicInbox::Spawn::nodatacow_dir($dir); # for journal/shm/wal
+                require PublicInbox::Syscall;
+                PublicInbox::Syscall::nodatacow_dir($dir); # for journal/shm/wal
                 open my $fh, '+>>', $f or die "failed to open $f: $!";
-                PublicInbox::Spawn::nodatacow_fd(fileno($fh));
         }
         $self;
 }
diff --git a/lib/PublicInbox/Spawn.pm b/lib/PublicInbox/Spawn.pm
index e0a51c21..137b8087 100644
--- a/lib/PublicInbox/Spawn.pm
+++ b/lib/PublicInbox/Spawn.pm
@@ -1,4 +1,4 @@
-# Copyright (C) 2016-2021 all contributors <meta@public-inbox.org>
+# Copyright (C) all contributors <meta@public-inbox.org>
 # License: AGPL-3.0+ <https://www.gnu.org/licenses/agpl-3.0.txt>
 #
 # This allows vfork to be used for spawning subprocesses if
@@ -21,7 +21,7 @@ use Symbol qw(gensym);
 use Fcntl qw(LOCK_EX SEEK_SET);
 use IO::Handle ();
 use PublicInbox::ProcessPipe;
-our @EXPORT_OK = qw(which spawn popen_rd run_die nodatacow_dir);
+our @EXPORT_OK = qw(which spawn popen_rd run_die);
 our @RLIMITS = qw(RLIMIT_CPU RLIMIT_CORE RLIMIT_DATA);
 
 BEGIN {
@@ -268,62 +268,12 @@ void recv_cmd4(PerlIO *s, SV *buf, STRLEN n)
 #endif /* defined(CMSG_SPACE) && defined(CMSG_LEN) */
 ALL_LIBC
 
-# btrfs on Linux is copy-on-write (COW) by default.  As of Linux 5.7,
-# this still leads to fragmentation for SQLite and Xapian files where
-# random I/O happens, so we disable COW just for SQLite files and Xapian
-# directories.  Disabling COW disables checksumming, so we only do this
-# for regeneratable files, and not canonical git storage (git doesn't
-# checksum refs, only data under $GIT_DIR/objects).
-        my $set_nodatacow = $^O eq 'linux' ? <<'SET_NODATACOW' : '';
-#include <sys/ioctl.h>
-#include <sys/vfs.h>
-#include <linux/magic.h>
-#include <linux/fs.h>
-#include <dirent.h>
-
-void nodatacow_fd(int fd)
-{
-        struct statfs buf;
-        int val = 0;
-
-        if (fstatfs(fd, &buf) < 0) {
-                fprintf(stderr, "fstatfs: %s\\n", strerror(errno));
-                return;
-        }
-
-        /* only btrfs is known to have this problem, so skip for non-btrfs */
-        if (buf.f_type != BTRFS_SUPER_MAGIC)
-                return;
-
-        if (ioctl(fd, FS_IOC_GETFLAGS, &val) < 0) {
-                fprintf(stderr, "FS_IOC_GET_FLAGS: %s\\n", strerror(errno));
-                return;
-        }
-        val |= FS_NOCOW_FL;
-        if (ioctl(fd, FS_IOC_SETFLAGS, &val) < 0)
-                fprintf(stderr, "FS_IOC_SET_FLAGS: %s\\n", strerror(errno));
-}
-
-void nodatacow_dir(const char *dir)
-{
-        DIR *dh = opendir(dir);
-        int fd;
-
-        if (!dh) croak("opendir(%s): %s", dir, strerror(errno));
-        fd = dirfd(dh);
-        if (fd >= 0)
-                nodatacow_fd(fd);
-        /* ENOTSUP probably won't happen under Linux... */
-        closedir(dh);
-}
-SET_NODATACOW
-
         my $inline_dir = $ENV{PERL_INLINE_DIRECTORY} //= (
                         $ENV{XDG_CACHE_HOME} //
                         ( ($ENV{HOME} // '/nonexistent').'/.cache' )
                 ).'/public-inbox/inline-c';
         warn "$inline_dir exists, not writable\n" if -e $inline_dir && !-w _;
-        $set_nodatacow = $all_libc = undef unless -d _ && -w _;
+        $all_libc = undef unless -d _ && -w _;
         if (defined $all_libc) {
                 my $f = "$inline_dir/.public-inbox.lock";
                 open my $oldout, '>&', \*STDOUT or die "dup(1): $!";
@@ -337,17 +287,10 @@ SET_NODATACOW
                 # CentOS 7.x ships Inline 0.53, 0.64+ has built-in locking
                 flock($fh, LOCK_EX) or die "LOCK_EX($f): $!";
                 eval <<'EOM';
-use Inline C => $all_libc.$set_nodatacow, BUILD_NOISY => 1;
+use Inline C => $all_libc, BUILD_NOISY => 1;
 EOM
                 my $err = $@;
                 my $ndc_err = '';
-                if ($err && $set_nodatacow) { # missing Linux kernel headers
-                        $ndc_err = "with set_nodatacow: <\n$err\n>\n";
-                        undef $set_nodatacow;
-                        eval <<'EOM';
-use Inline C => $all_libc, BUILD_NOISY => 1;
-EOM
-                };
                 $err = $@;
                 open(STDERR, '>&', $olderr) or warn "restore stderr: $!";
                 open(STDOUT, '>&', $oldout) or warn "restore stdout: $!";
@@ -356,22 +299,13 @@ EOM
                         my @msg = <$fh>;
                         warn "Inline::C build failed:\n",
                                 $ndc_err, $err, "\n", @msg;
-                        $set_nodatacow = $all_libc = undef;
-                } elsif ($ndc_err) {
-                        warn "Inline::C build succeeded w/o set_nodatacow\n",
-                                "error $ndc_err";
+                        $all_libc = undef;
                 }
         }
         unless ($all_libc) {
                 require PublicInbox::SpawnPP;
                 *pi_fork_exec = \&PublicInbox::SpawnPP::pi_fork_exec
         }
-        unless ($set_nodatacow) {
-                require PublicInbox::NDC_PP;
-                no warnings 'once';
-                *nodatacow_fd = \&PublicInbox::NDC_PP::nodatacow_fd;
-                *nodatacow_dir = \&PublicInbox::NDC_PP::nodatacow_dir;
-        }
 } # /BEGIN
 
 sub which ($) {
diff --git a/lib/PublicInbox/Syscall.pm b/lib/PublicInbox/Syscall.pm
index c00385b9..bcfae2cb 100644
--- a/lib/PublicInbox/Syscall.pm
+++ b/lib/PublicInbox/Syscall.pm
@@ -5,7 +5,7 @@
 # This license differs from the rest of public-inbox
 #
 # This module is Copyright (c) 2005 Six Apart, Ltd.
-# Copyright (C) 2019-2021 all contributors <meta@public-inbox.org>
+# Copyright (C) all contributors <meta@public-inbox.org>
 #
 # All rights reserved.
 #
@@ -68,6 +68,7 @@ our (
      $SYS_renameat2,
      );
 
+my $SYS_fstatfs; # don't need fstatfs64, just statfs.f_type
 my $SFD_CLOEXEC = 02000000; # Perl does not expose O_CLOEXEC
 our $no_deprecated = 0;
 
@@ -96,18 +97,21 @@ if ($^O eq "linux") {
         $SYS_epoll_wait   = 256;
         $SYS_signalfd4 = 327;
         $SYS_renameat2 //= 353;
+        $SYS_fstatfs = 100;
     } elsif ($machine eq "x86_64") {
         $SYS_epoll_create = 213;
         $SYS_epoll_ctl    = 233;
         $SYS_epoll_wait   = 232;
         $SYS_signalfd4 = 289;
         $SYS_renameat2 //= 316;
+        $SYS_fstatfs = 138;
     } elsif ($machine eq 'x32') {
         $SYS_epoll_create = 1073742037;
         $SYS_epoll_ctl = 1073742057;
         $SYS_epoll_wait = 1073742056;
         $SYS_signalfd4 = 1073742113;
         $SYS_renameat2 //= 0x40000000 + 316;
+        $SYS_fstatfs = 138;
     } elsif ($machine eq 'sparc64') {
         $SYS_epoll_create = 193;
         $SYS_epoll_ctl = 194;
@@ -116,6 +120,7 @@ if ($^O eq "linux") {
         $SYS_signalfd4 = 317;
         $SYS_renameat2 //= 345;
         $SFD_CLOEXEC = 020000000;
+        $SYS_fstatfs = 158;
     } elsif ($machine =~ m/^parisc/) {
         $SYS_epoll_create = 224;
         $SYS_epoll_ctl    = 225;
@@ -129,6 +134,7 @@ if ($^O eq "linux") {
         $u64_mod_8        = 1;
         $SYS_signalfd4 = 313;
         $SYS_renameat2 //= 357;
+        $SYS_fstatfs = 100;
     } elsif ($machine eq "ppc") {
         $SYS_epoll_create = 236;
         $SYS_epoll_ctl    = 237;
@@ -136,6 +142,7 @@ if ($^O eq "linux") {
         $u64_mod_8        = 1;
         $SYS_signalfd4 = 313;
         $SYS_renameat2 //= 357;
+        $SYS_fstatfs = 100;
     } elsif ($machine =~ m/^s390/) {
         $SYS_epoll_create = 249;
         $SYS_epoll_ctl    = 250;
@@ -143,6 +150,7 @@ if ($^O eq "linux") {
         $u64_mod_8        = 1;
         $SYS_signalfd4 = 322;
         $SYS_renameat2 //= 347;
+        $SYS_fstatfs = 100;
     } elsif ($machine eq "ia64") {
         $SYS_epoll_create = 1243;
         $SYS_epoll_ctl    = 1244;
@@ -165,6 +173,7 @@ if ($^O eq "linux") {
         $no_deprecated    = 1;
         $SYS_signalfd4 = 74;
         $SYS_renameat2 //= 276;
+        $SYS_fstatfs = 44;
     } elsif ($machine =~ m/arm(v\d+)?.*l/) {
         # ARM OABI
         $SYS_epoll_create = 250;
@@ -173,6 +182,7 @@ if ($^O eq "linux") {
         $u64_mod_8        = 1;
         $SYS_signalfd4 = 355;
         $SYS_renameat2 //= 382;
+        $SYS_fstatfs = 100;
     } elsif ($machine =~ m/^mips64/) {
         $SYS_epoll_create = 5207;
         $SYS_epoll_ctl    = 5208;
@@ -180,6 +190,7 @@ if ($^O eq "linux") {
         $u64_mod_8        = 1;
         $SYS_signalfd4 = 5283;
         $SYS_renameat2 //= 5311;
+        $SYS_fstatfs = 5135;
     } elsif ($machine =~ m/^mips/) {
         $SYS_epoll_create = 4248;
         $SYS_epoll_ctl    = 4249;
@@ -187,6 +198,7 @@ if ($^O eq "linux") {
         $u64_mod_8        = 1;
         $SYS_signalfd4 = 4324;
         $SYS_renameat2 //= 4351;
+        $SYS_fstatfs = 4100;
     } else {
         # as a last resort, try using the *.ph files which may not
         # exist or may be wrong
@@ -323,6 +335,38 @@ sub rename_noreplace ($$) {
         }
 }
 
+sub nodatacow_fh {
+        return if !defined($SYS_fstatfs);
+        my $buf = '';
+        vec($buf, 120 * 8 - 1, 1) = 0;
+        my ($fh) = @_;
+        syscall($SYS_fstatfs, fileno($fh), $buf) == 0 or
+                return warn("fstatfs: $!\n");
+        my $f_type = unpack('l!', $buf); # statfs.f_type is a signed word
+        return if $f_type != 0x9123683E; # BTRFS_SUPER_MAGIC
+
+        state ($FS_IOC_GETFLAGS, $FS_IOC_SETFLAGS);
+        unless (defined $FS_IOC_GETFLAGS) {
+                if (substr($Config{byteorder}, 0, 4) eq '1234') {
+                        $FS_IOC_GETFLAGS = 0x80086601;
+                        $FS_IOC_SETFLAGS = 0x40086602;
+                } else { # Big endian
+                        $FS_IOC_GETFLAGS = 0x40086601;
+                        $FS_IOC_SETFLAGS = 0x80086602;
+                }
+        }
+        ioctl($fh, $FS_IOC_GETFLAGS, $buf) //
+                return warn("FS_IOC_GET_FLAGS: $!\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_SET_FLAGS: $!\n");
+}
+
+sub nodatacow_dir {
+        if (open my $fh, '<', $_[0]) { nodatacow_fh($fh) }
+}
+
 1;
 
 =head1 WARRANTY
diff --git a/lib/PublicInbox/Xapcmd.pm b/lib/PublicInbox/Xapcmd.pm
index 44e0f8e5..10685636 100644
--- a/lib/PublicInbox/Xapcmd.pm
+++ b/lib/PublicInbox/Xapcmd.pm
@@ -1,8 +1,9 @@
-# Copyright (C) 2018-2021 all contributors <meta@public-inbox.org>
+# Copyright (C) all contributors <meta@public-inbox.org>
 # License: AGPL-3.0+ <https://www.gnu.org/licenses/agpl-3.0.txt>
 package PublicInbox::Xapcmd;
 use strict;
-use PublicInbox::Spawn qw(which popen_rd nodatacow_dir);
+use PublicInbox::Spawn qw(which popen_rd);
+use PublicInbox::Syscall;
 use PublicInbox::Admin qw(setup_signals);
 use PublicInbox::Over;
 use PublicInbox::SearchIdx;
@@ -211,7 +212,7 @@ sub prepare_run {
                 my $v = PublicInbox::Search::SCHEMA_VERSION();
                 my $wip = File::Temp->newdir("xapian$v-XXXX", DIR => $dir);
                 $tmp->{$old} = $wip;
-                nodatacow_dir($wip->dirname);
+                PublicInbox::Syscall::nodatacow_dir($wip->dirname);
                 push @queue, [ $old, $wip ];
         } elsif (defined $old) {
                 opendir my $dh, $old or die "Failed to opendir $old: $!\n";
@@ -242,7 +243,7 @@ sub prepare_run {
                         same_fs_or_die($old, $wip->dirname);
                         my $cur = "$old/$dn";
                         push @queue, [ $src // $cur , $wip ];
-                        nodatacow_dir($wip->dirname);
+                        PublicInbox::Syscall::nodatacow_dir($wip->dirname);
                         $tmp->{$cur} = $wip;
                 }
                 # mark old shards to be unlinked
@@ -443,7 +444,7 @@ sub cpdb ($$) { # cb_spawn callback
                 $ft = File::Temp->newdir("$new.compact-XXXX", DIR => $dir);
                 setup_signals();
                 $tmp = $ft->dirname;
-                nodatacow_dir($tmp);
+                PublicInbox::Syscall::nodatacow_dir($tmp);
         } else {
                 $tmp = $new;
         }
diff --git a/t/nodatacow.t b/t/nodatacow.t
index 19247c10..0940d908 100644
--- a/t/nodatacow.t
+++ b/t/nodatacow.t
@@ -1,48 +1,42 @@
 #!perl -w
-# Copyright (C) 2020-2021 all contributors <meta@public-inbox.org>
+# Copyright (C) all contributors <meta@public-inbox.org>
 # License: AGPL-3.0+ <https://www.gnu.org/licenses/agpl-3.0.txt>
 use strict; use v5.10.1; use PublicInbox::TestCommon;
 use File::Temp 0.19;
-use_ok 'PublicInbox::NDC_PP';
+use_ok 'PublicInbox::Syscall';
+
+# btrfs on Linux is copy-on-write (COW) by default.  As of Linux 5.7,
+# this still leads to fragmentation for SQLite and Xapian files where
+# random I/O happens, so we disable COW just for SQLite files and Xapian
+# directories.  Disabling COW disables checksumming, so we only do this
+# for regeneratable files, and not canonical git storage (git doesn't
+# checksum refs, only data under $GIT_DIR/objects).
 
 SKIP: {
         my $nr = 2;
         skip 'test is Linux-only', $nr if $^O ne 'linux';
         my $dir = $ENV{BTRFS_TESTDIR};
         skip 'BTRFS_TESTDIR not defined', $nr unless defined $dir;
-        require_cmd('chattr', 1) or skip 'chattr(1) not installed', $nr;
+
         my $lsattr = require_cmd('lsattr', 1) or
                 skip 'lsattr(1) not installed', $nr;
+
         my $tmp = File::Temp->newdir('nodatacow-XXXX', DIR => $dir);
         my $dn = $tmp->dirname;
 
         my $name = "$dn/pp.f";
         open my $fh, '>', $name or BAIL_OUT "open($name): $!";
-        my $pp_sub = \&PublicInbox::NDC_PP::nodatacow_fd;
-        $pp_sub->(fileno($fh));
+        PublicInbox::Syscall::nodatacow_fh($fh);
         my $res = xqx([$lsattr, $name]);
+
+        BAIL_OUT "lsattr(1) fails in $dir" if $?;
         like($res, qr/C.*\Q$name\E/, "`C' attribute set on fd with pure Perl");
 
         $name = "$dn/pp.d";
         mkdir($name) or BAIL_OUT "mkdir($name) $!";
-        PublicInbox::NDC_PP::nodatacow_dir($name);
+        PublicInbox::Syscall::nodatacow_dir($name);
         $res = xqx([$lsattr, '-d', $name]);
         like($res, qr/C.*\Q$name\E/, "`C' attribute set on dir with pure Perl");
-
-        $name = "$dn/ic.f";
-        my $ic_sub = \&PublicInbox::Spawn::nodatacow_fd;
-        $pp_sub == $ic_sub and
-                skip 'Inline::C or Linux kernel headers missing', 2;
-        open $fh, '>', $name or BAIL_OUT "open($name): $!";
-        $ic_sub->(fileno($fh));
-        $res = xqx([$lsattr, $name]);
-        like($res, qr/C.*\Q$name\E/, "`C' attribute set on fd with Inline::C");
-
-        $name = "$dn/ic.d";
-        mkdir($name) or BAIL_OUT "mkdir($name) $!";
-        PublicInbox::Spawn::nodatacow_dir($name);
-        $res = xqx([$lsattr, '-d', $name]);
-        like($res, qr/C.*\Q$name\E/, "`C' attribute set on dir with Inline::C");
 };
 
 done_testing;