Re: [PATCH] Btrfs: add a disk info ioctl to get the disks attached to a filesystem

[Josef Bacik <josef@redhat.com>]

On Wed, Sep 29, 2010 at 12:28:51AM +0200, Goffredo Baroncelli wrote:
> Hi Josef,
> 
> what about using your ioctl to exporting also other info ? For example devid, 
> size, bytes, uuid ...
> 
> I know that btrfs filesystem-show does the same, but it reads the partition 
> (the disk) instead of query the filesystem. That means:
> - It work even for unmounted filesystem (which is good)
> - The results are inaccurate for a mounted filesystem, because the read data 
> is not valid until a flush of the pages (which is bad.. very bad).
>

Well a) the data on disk is always valid, thats the point :).  And b) the only
way the data is not uptodate is if we happened to add/remove/resize a disk right
before running btrfs-show, something that isn't going to happen often.  So I
think btrfs-show solves this problem well enough.  My ioctl is to give apps a
nice quick programmable way to get the list of disks in the fs so they can do
whatever they want instead of having to ship a libbtrfs or some such thing and
make them use that.  Thanks,

Josef