[libvirt] [TCK PATCHv2] block devices: allow specification of size for safety

[Eric Blake <eblake@xxxxxxxxxx>]

I was getting failures of domain/103-blockdev-save-restore.t when
connecting as qemu:///session, since my uid could stat /dev/sdb but
not open it.  That test now skips for unprivileged users, as well as
adds a layer of sanity checking against expected size to avoid
trashing the wrong device.

* conf/default.cfg (host_block_devices): Document optional size.
* lib/Sys/Virt/TCK.pm (get_host_block_device): If optional size is
supplied, skip a device that does not match.  Also, avoid devices
that can't be opened.
---

Changes from v1:
+ perl is more idiomatic
+ guarantee that BLK is closed, even if sysseek failed
+ mention /dev/disk/by-id/ trick in default.cfg

 conf/default.cfg    |    8 ++++++++
 lib/Sys/Virt/TCK.pm |   14 +++++++++++++-
 2 files changed, 21 insertions(+), 1 deletions(-)

diff --git a/conf/default.cfg b/conf/default.cfg
index 01f438c..d749f5f 100644
--- a/conf/default.cfg
+++ b/conf/default.cfg
@@ -134,5 +134,13 @@ host_pci_devices = (
 # the test suite itself needs to create partitions.
 # The disks should be at *least* 512 MB in size
 host_block_devices = (
+# Each block device is either a raw path
 #  /dev/vdb
+# or a path plus size in 1k blocks, as in /proc/partitions, to avoid
+# trashing the wrong device
+#  {
+#    path = /dev/disk/by-id/usb-Generic_Flash_Disk_9B46E3C5-0:0
+#    size = 989184
+#  }
+# Can list more than on block device if many are available
 )
diff --git a/lib/Sys/Virt/TCK.pm b/lib/Sys/Virt/TCK.pm
index 9cdef09..7d97314 100644
--- a/lib/Sys/Virt/TCK.pm
+++ b/lib/Sys/Virt/TCK.pm
@@ -33,6 +33,7 @@ use IO::Uncompress::Gunzip qw(gunzip);
 use IO::Uncompress::Bunzip2 qw(bunzip2);
 use XML::XPath;
 use Carp qw(cluck carp);
+use Fcntl qw(O_RDONLY SEEK_END);

 use Test::Builder;
 use Sub::Uplevel qw(uplevel);
@@ -833,7 +834,18 @@ sub get_host_block_device {
     my $self = shift;
     my $devindex = @_ ? shift : 0;

-    return $self->config("host_block_devices/[$devindex]", undef);
+    my $device = $self->config("host_block_devices/[$devindex]/path", undef);
+    my $kb_blocks = $self->config("host_block_devices/[$devindex]/size", 0);
+
+    $device ||= $self->config("host_block_devices/[$devindex]", undef);
+
+    if ($kb_blocks && $device) {
+	my $match = (sysopen(BLK, $device, O_RDONLY)
+		     && sysseek(BLK, 0, SEEK_END) == $kb_blocks * 1024);
+	close BLK;
+	$match or return undef;
+    }
+    return $device;
 }

 1;
-- 
1.6.6.1

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