log2phys - lookup physical locations of file extents on Darwin

log2phys

#!/usr/bin/perl

use v5.10;
use strict;

# https://github.com/apple-oss-distributions/xnu/blob/94d3b452840153a99b38a3a9659680b2a006908e/bsd/sys/fcntl.h#L326C9-L326C23
use constant F_LOG2PHYS_EXT => 65;

foreach (@ARGV) {
    say "==== $_ ====";
    open my $fh, "<",  $_ or die "open: $!";

    my @stat = stat $fh or die "fstat: $!";
    printf "st_dev:  % 20d    st_ino: % 20d\n", $stat[0], $stat[1];
    my $sz = $stat[7];

    my $pos = 0;
    while ($pos < $sz) {
        # from fcntl(2):
        #
        # struct log2phys {
        #     u_int32_t l2p_flags;        /* unused so far */
        #     off_t     l2p_contigbytes;  /* IN: number of bytes to be queried;
        #                                    OUT: number of contiguous bytes allocated at this position */
        #     off_t     l2p_devoffset;    /* IN: bytes into file;
        #                                    OUT: bytes into device */
        # };
        my $log2phys = pack("LQQ", 0, $sz - $pos, $pos);
        fcntl $fh, F_LOG2PHYS_EXT, $log2phys or die "fcntl: $!";
        my ($l2p_flags, $l2p_contigbytes, $l2p_devoffset) = unpack "LQQ", $log2phys;

        printf "logaddr: % 20d    flags: %08x    len: % 20d    physaddr: % 20d\n", $pos, $l2p_flags, $l2p_contigbytes, $l2p_devoffset;

        $pos += $l2p_contigbytes;
    }

    say "";
}