lkml.org 
[lkml]   [2020]   [Jan]   [14]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH V2] brd: check parameter validation before register_blkdev func
On Tue, Jan 14, 2020 at 05:16:57PM +0800, Ming Lei wrote:
> On Mon, Jan 13, 2020 at 09:43:23PM +0800, Zhiqiang Liu wrote:
> > In brd_init func, rd_nr num of brd_device are firstly allocated
> > and add in brd_devices, then brd_devices are traversed to add each
> > brd_device by calling add_disk func. When allocating brd_device,
> > the disk->first_minor is set to i * max_part, if rd_nr * max_part
> > is larger than MINORMASK, two different brd_device may have the same
> > devt, then only one of them can be successfully added.
>
> It is just because disk->first_minor is >= 0x100000, then same dev_t
> can be allocated in blk_alloc_devt().
>
> MKDEV(disk->major, disk->first_minor + part->partno)
>
> But block layer does support extended dynamic devt allocation, and brd
> sets flag of GENHD_FL_EXT_DEVT too.
>
> So I think the correct fix is to fallback to extended dynamic allocation
> when running out of consecutive minor space.
>
> How about the following approach?
>
> And of course, ext devt allocation may fail too, but that is another
> generic un-solved issue: error handling isn't done for adding disk.
>
> diff --git a/drivers/block/brd.c b/drivers/block/brd.c
> index a8730cc4db10..9aa7ce7c9abf 100644
> --- a/drivers/block/brd.c
> +++ b/drivers/block/brd.c
> @@ -398,7 +398,16 @@ static struct brd_device *brd_alloc(int i)
> if (!disk)
> goto out_free_queue;
> disk->major = RAMDISK_MAJOR;
> - disk->first_minor = i * max_part;
> +
> + /*
> + * Clear .minors when running out of consecutive minor space since
> + * GENHD_FL_EXT_DEVT is set, and we can allocate from extended devt
> + */
> + if ((i * disk->minors) & ~MINORMASK)
> + disk->minors = 0;
> + else
> + disk->first_minor = i * disk->minors;
> +
> disk->fops = &brd_fops;
> disk->private_data = brd;
> disk->flags = GENHD_FL_EXT_DEVT;

But still suggest to limit 'max_part' <= 256, and the name is actually
misleading, which just reserves consecutive minors.

However, I don't think it is a good idea to add limit on device number.


Thanks,
Ming

\
 
 \ /
  Last update: 2020-01-14 10:47    [W:0.051 / U:0.112 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site