From 6be1ba8a63f53b4167262250be1c122c7c08f61d Mon Sep 17 00:00:00 2001

From: Richard Jones <rjones@redhat.com>

Date: Fri, 16 Jul 2010 18:11:56 +0100

Subject: [PATCH] df: Minimize the number of times we launch the libguestfs appliance.

This commit greatly improves the performance of the 'virt-df'

command by batching as many disks as possible onto a single appliance.

In many situations this means the appliance is launched only once,

versus one launch per domain as before.

However doing it this way is a lot more complex:

(1) Because of limits in Linux and virtio-blk, we can only attach

26 disks maximum at a time to the appliance.

(2) We have to use LVM filters (lvm-set-filter) to confine LVM to

the disks of a single guest.

(cherry picked from commit 45a4cd79215752234c4a5a47fb4c9c6741b1594c)

---

 tools/virt-df |  217 ++++++++++++++++++++++++++++++++++++++++++++++-----------

 1 files changed, 177 insertions(+), 40 deletions(-)

diff --git a/tools/virt-df b/tools/virt-df

index 45b7869..790dd6a 100755

--- a/tools/virt-df

+++ b/tools/virt-df

@@ -20,12 +20,11 @@ use warnings;

 use strict;

 use Sys::Guestfs;

-use Sys::Guestfs::Lib qw(open_guest get_partitions);

+use Sys::Guestfs::Lib qw(feature_available);

 use Pod::Usage;

 use Getopt::Long;

-use Data::Dumper;

-use XML::Writer;

+use File::Basename qw(basename);

 use POSIX qw(ceil);

 use Locale::TextDomain 'libguestfs';

@@ -151,9 +150,22 @@ if ($version) {

 # RHBZ#600977

 die __"virt-df: cannot use -h and --csv options together\n" if $human && $csv;

-# Open the guest handle.

+# Get the list of domains and block devices.

+#

+# We can't use Sys::Guestfs::Lib::open_guest here because we want to

+# create the libguestfs handle/appliance as few times as possible.

+#

+# If virt-df is called with no parameters, then run the libvirt

+# equivalent of "virsh list --all", get the XML for each domain, and

+# get the disk devices.

+#

+# If virt-df is called with parameters, assume it must either be a

+# single disk image filename, a list of disk image filenames, or a

+# single libvirt guest name.  Construct disk devices accordingly.

-if (@ARGV == 0) {

+my @domains = ();

+

+if (@ARGV == 0) {               # No params, use libvirt.

     my $conn;

     if ($uri) {

@@ -168,61 +180,186 @@ if (@ARGV == 0) {

     # https://bugzilla.redhat.com/show_bug.cgi?id=538041

     @doms = grep { $_->get_id () != 0 } @doms;

-    my @domnames = sort (map { $_->get_name () } @doms);

+    exit 0 unless @doms;

+

+    foreach my $dom (@doms) {

+        my @disks = get_disks_from_libvirt ($dom);

+        push @domains, { dom => $dom,

+                         name => $dom->get_name (),

+                         disks => \@disks }

+    }

+} elsif (@ARGV == 1) {          # One param, could be disk image or domname.

+    if (-e $ARGV[0]) {

+        push @domains, { name => basename ($ARGV[0]),

+                         disks => [ $ARGV[0] ] }

+    } else {

+        my $conn;

-    if (@domnames) {

-        print_title ();

-        foreach (@domnames) {

-            eval { do_df ($_); };

-            warn $@ if $@;

+        if ($uri) {

+            $conn = Sys::Virt->new (readonly => 1, address => $uri);

+        } else {

+            $conn = Sys::Virt->new (readonly => 1);

         }

+

+        my $dom = $conn->get_domain_by_name ($ARGV[0])

+            or die __x("{name} is not the name of a libvirt domain\n",

+                       name => $ARGV[0]);

+        my @disks = get_disks_from_libvirt ($dom);

+        push @domains, { dom => $dom,

+                         name => $dom->get_name (),

+                         disks => \@disks }

     }

-} else {

-    print_title ();

-    do_df (@ARGV);

+} else {                        # >= 2 params, all disk images.

+    push @domains, { name => basename ($ARGV[0]),

+                     disks => \@ARGV }

 }

-sub do_df

+sub get_disks_from_libvirt

 {

-    my $g;

+    my $dom = shift;

+    my $xml = $dom->get_xml_description ();

-    if ($uri) {

-        $g = open_guest (\@_, address => $uri);

-    } else {

-        $g = open_guest (\@_);

+    my $p = XML::XPath->new (xml => $xml);

+    my @disks = $p->findnodes ('//devices/disk/source/@dev');

+    push (@disks, $p->findnodes ('//devices/disk/source/@file'));

+

+    # Code in Sys::Guestfs::Lib dies here if there are no disks at all.

+

+    return map { $_->getData } @disks;

+}

+

+# Sort the domains by name for display.

+@domains = sort { $a->{name} cmp $b->{name} } @domains;

+

+# Since we got this far, we're somewhat sure we're going to

+# get to print the result, so display the title.

+print_title ();

+

+# To minimize the number of times we have to launch the appliance,

+# shuffle as many domains together as we can, but not exceeding 26

+# disks per request.  (26 = # of letters in the English alphabet, and

+# we are only confident that /dev/sd[a-z] will work because of various

+# limits).

+my $n = 0;

+my @request = ();

+while (@domains) {

+    while (@domains) {

+        my $c = @{$domains[0]->{disks}};

+        last if $n + $c > 26;

+        push @request, shift @domains;

+    }

+    multi_df (@request);

+}

+

+sub multi_df

+{

+    local $_;

+    my $g = Sys::Guestfs->new ();

+

+    my ($d, $disk);

+

+    foreach $d (@_) {

+        foreach $disk (@{$d->{disks}}) {

+            $g->add_drive_ro ($disk);

+        }

     }

     $g->launch ();

+    my $has_lvm2 = feature_available ($g, "lvm2");

-    my @partitions = get_partitions ($g);

-

-    # Think of a printable name for this domain.  Just choose the

-    # first parameter passed to this function, which will work for

-    # most cases (it'll either be the domain name or the first disk

-    # image name).

-    my $domname = $_[0];

-

-    # Mount each partition in turn, and if mountable, do a statvfs on it.

-    foreach my $partition (@partitions) {

-        my %stat;

-        eval {

-            $g->mount_ro ($partition, "/");

-            %stat = $g->statvfs ("/");

-        };

-        if (!$@) {

-            print_stat ($domname, $partition, \%stat);

+    my @devices = $g->list_devices ();

+    my @partitions = $g->list_partitions ();

+

+    my $n = 0;

+    foreach $d (@_) {

+        my $name = $d->{name};

+        my $nr_disks = @{$d->{disks}};

+

+        # Filter LVM to only the devices applying to the original domain.

+        my @devs = @devices[$n .. $n+$nr_disks-1];

+        $g->lvm_set_filter (\@devs) if $has_lvm2;

+

+        # Find which whole devices (RHBZ#590167), partitions and LVs

+        # contain mountable filesystems.  Stat those which are

+        # mountable, and ignore the others.

+        foreach (@devs) {

+            try_df ($name, $g, $_, canonical_dev ($_, $n));

+        }

+        foreach (filter_partitions (\@devs, @partitions)) {

+            try_df ($name, $g, $_, canonical_dev ($_, $n));

+        }

+        if ($has_lvm2) {

+            foreach ($g->lvs ()) {

+                try_df ($name, $g, $_);

+            }

+        }

+

+        $n += $nr_disks;

+    }

+}

+

+sub filter_partitions

+{

+    my $devs = shift;

+    my @devs = @$devs;

+    my @r;

+

+    foreach my $p (@_) {

+        foreach my $d (@devs) {

+            if ($p =~ /^$d\d/) {

+                push @r, $p;

+                last;

+            }

         }

-        $g->umount_all ();

     }

+

+    return @r;

+}

+

+# Calculate the canonical name for a device.

+# eg: /dev/vdb1 when offset = 1

+#     => canonical name is /dev/sda1

+sub canonical_dev

+{

+    local $_;

+    my $dev = shift;

+    my $offset = shift;

+

+    return $dev unless $dev =~ m{^/dev/.d([a-z])(\d*)$};

+    my $disk = $1;

+    my $partnum = $2;

+

+    $disk = chr (ord ($disk) - $offset);

+

+    return "/dev/sd$disk$partnum"

+}

+

+sub try_df

+{

+    local $_;

+    my $domname = shift;

+    my $g = shift;

+    my $dev = shift;

+    my $display = shift || $dev;

+

+    my %stat;

+    eval {

+        $g->mount_ro ($dev, "/");

+        %stat = $g->statvfs ("/");

+    };

+    if (!$@) {

+        print_stat ($domname, $display, \%stat);

+    }

+    $g->umount_all ();

 }

 sub print_stat

 {

     my $domname = shift;

-    my $partition = shift;

+    my $dev = shift;

     my $stat = shift;

-    my @cols = ($domname, $partition);

+    my @cols = ($domname, $dev);

     if (!$inodes) {

         my $bsize = $stat->{bsize};	# block size

-- 

1.7.1