On 2020/1/14 17:45, Ming Lei wrote: > 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 for your patient replyI will resend the v3 patch as your suggestion. Changes in v3: 1)clear .minors when running out of consecutive minor space in brd_alloc. 2)remove limit of rd_nr
