[Libguestfs] [PATCH] Correctly detect the size of a block device over SSH

[Matthew Booth]

On 17/08/10 12:18, Richard W.M. Jones wrote:
> On Wed, Aug 04, 2010 at 04:14:45PM +0100, Matthew Booth wrote:
>> When fetching a storage volume over SSH, we were detecting its size with a
>> simple 'stat -c %s'. While this works fine for files, it won't return the
>> correct size of a block device.
>>
>> This patch uses the output of 'blockdev --getsize64' for block devices, and stat
>> as before for regular files.
>>
>> Fixes RHBZ#620698
>> ---
>>   lib/Sys/VirtV2V/Transfer/SSH.pm |   16 +++++++++++++++-
>>   1 files changed, 15 insertions(+), 1 deletions(-)
>>
>> diff --git a/lib/Sys/VirtV2V/Transfer/SSH.pm b/lib/Sys/VirtV2V/Transfer/SSH.pm
>> index 66ec294..5f54f0e 100644
>> --- a/lib/Sys/VirtV2V/Transfer/SSH.pm
>> +++ b/lib/Sys/VirtV2V/Transfer/SSH.pm
>> @@ -138,7 +138,21 @@ sub _connect
>>           push(@command, 'ssh');
>>           push(@command, '-l', $username) if (defined($username));
>>           push(@command, $host);
>> -        push(@command, "stat -c %s $path; cat $path");
>> +
>> +        # Return the size of the remote path on the first line, followed by its
>> +        # contents.
>> +        # The bit arithmetic with the output of stat is a translation into shell
>> +        # of the S_ISBLK macro. If the remote device is a block device, stat
>> +        # will simply return the size of the block device inode. In this case,
>> +        # we use the output of blockdev --getsize64 instead.
>> +        push(@command,
>> +            "dev=$path; ".
>> +            'if [[ $(((0x$(stat -L -c %f $dev)&0170000)>>12)) == 6 ]]; then '.
>> +              'blockdev --getsize64 $dev; '.
>> +            'else '.
>> +              'stat -L -c %s $dev; '.
>> +            'fi; '.
>> +            'cat $dev');
>>
>>           # Close the ends of the pipes we don't need
>>           close($stdin_write);
>
> Yikes.
>
> Not an easier way to ask if a filename is a block device?  Like
> maybe: test -b $dev

I've actually already pushed this, but I'll update it anyway. Thanks :)

Matt
-- 
Matthew Booth, RHCA, RHCSS
Red Hat Engineering, Virtualisation Team

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