On Tue, Jan 25, 2011 at 11:15:11AM +1100, Chris Samuel wrote:
> /*
> * CC'd to linux-kernel in case they have any feedback on this.
> *
> * Long thread, trying to work out why mkfs.btrfs failed to
> * make a filesystem on an encrypted loopback mount called
> * /dev/loop2. Cause turned out to be mkfs.btrfs calling
> * LOOP_GET_STATUS to find out if the block device was mounted
> * and getting a truncated device name back and so it later
> * fails when lstat() is called on the truncated device path.
> *
> * The long device name for the encrypted loopback mount was
> * because /dev/disk/by-id/$ID was used when Felix created it
> * to cope with devices moving around.
> */
>
> On 25/01/11 00:01, Felix Blanke wrote:
>
> > you were talking about the LOOP_GET_STATUS function. I'm not
> > quite sure where does it came from. Is it part of the kernel?
> > Or does it come from the util-linux package?
>
> It's in the kernel, and there is both LOOP_GET_STATUS (old
> implementation) and LOOP_GET_STATUS64 (new implementation).
>
> They return structures called loop_info and loop_info64
> respectively and both are defined in include/linux/loop.h .
>
> Sadly in both cases the lengths of paths are defined to be
> LO_NAME_SIZE which is currently 64 and hence either
> implementation will cause the problematic:
>
> lstat("/dev/disk/by-id/ata-INTEL_SSDSA2M160G2GC_CVPO939201JX160AGN-par",
> 0x7fffa30b3cf0) = -1 ENOENT (No such file or directory)
>
> I've CC'd this to the LKML in case they have any feedback on
> this apparent problem with the API.
Since 2.6.37, you can get full path to the backing file from sys:
cat /sys/block/loopX/loop/backing_fileSee http://linux.derkeiler.com/Mailing-Lists/Kernel/2010-07/msg10996.html HTH, Petr -- Petr Uzel IRC: ptr_uzl @ freenode
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