A: No.
Q: Should I include quotations after my reply?
http://daringfireball.net/2007/07/on_top
On Thu, Mar 03, 2016 at 03:52:20AM +0000, Ning, Yu wrote:
> Well, virtio_blk does use dynamic major number allocation, but the
> allocated block major just happens to fall in the "experimental" range
> (240-254)...
That all depends on what else is registered in the system at the moment.
> In more detail:
>
> virtio_blk calls register_blkdev() with major = 0 in init()
> (drivers/block/virtio_blk.c:872):
>
> major = register_blkdev(0, "virtblk");
>
> This line has been there since day one. And register_blkdev() implements
> dynamic major allocation pretty straightforwardly:
>
> /* temporary */
> if (major == 0) {
> for (index = ARRAY_SIZE(major_names)-1; index > 0; index--) {
> if (major_names[index] == NULL)
> break;
> }
>
> So it goes from index = 254 to 1 and picks the first unused.
> Apparently, there's a good chance that the allocated major is between
> 240-254 (although lower numbers are also possible, theoretically).
> Indeed, we always get 253 for virtio_blk with the x86_64 Android
> emulator kernel.
>
> But "dynamic" means we can't rely on checking major == 253 to detect
> virtio_blk.
Nor should you, why would you care?
> That's why we are doing a fnmatch() using pattern
> /sys/devices/*/block/vd* instead. Is that the recommended approach?
Yes, or just look at the device node that is already created in /dev/
for you automatially by devtmpfs. Doesn't that work as expected today?
I still don't understand the issue you are having here at all, sorry.
greg k-h
