[libvirt] [TCK PATCHv4] block devices: allow specification of size for safety

[Eric Blake]

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.
---

Thanks again to Jim and Daniel for the helpful feedback.
Here's the version I actually pushed, based on your feedback.

changes from v3:
completely determine $device before moving on to $kb_blocks
early exit if $device is undef after querying cfg file
reduce scope of $match

 conf/default.cfg    |    8 ++++++++
 lib/Sys/Virt/TCK.pm |   15 ++++++++++++++-
 2 files changed, 22 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..2485d0f 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 +834,19 @@ 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)
+		  || $self->config("host_block_devices/[$devindex]", undef));
+    return undef unless $device;
+
+    my $kb_blocks = $self->config("host_block_devices/[$devindex]/size", 0);
+
+    # Filter out devices that the current user can't open.
+    sysopen(BLK, $device, O_RDONLY) or return undef;
+    my $match = ($kb_blocks ? sysseek(BLK, 0, SEEK_END) == $kb_blocks * 1024
+		 : 1);
+    close BLK;
+
+    return $match ? $device : undef;
 }

 1;
-- 
1.6.6.1