On 03/09/2016 12:21 AM, NeilBrown wrote: > > When alloc_disk(0) or alloc_disk-node(0, XX) is used, the ->major > number is completely ignored: all devices are allocated with a > major of BLOCK_EXT_MAJOR. > > So there is no point allocating pmem_major. > > Signed-off-by: NeilBrown <[email protected]>
Tested-by: Boaz Harrosh <[email protected]> Yes I sent in the same exact patch several times. This is not the only driver that has this "wasted code" BTW. I hope it will be finally removed. Thanks Neil Boaz > --- > drivers/nvdimm/pmem.c | 19 +------------------ > 1 file changed, 1 insertion(+), 18 deletions(-) > > Hi Dan et al, > I was recently educating myself about the behavior of alloc_disk(0). > As I understand it, the ->major is ignored and all device numbers for all > partitions (including '0') are allocated on demand with major number of > BLOCK_EXT_MAJOR. > > So I was a little surprised to find that pmem.c allocated a major > number which is never used - historical anomaly I suspect. > I was a bit more surprised at the comment in: > > Commit: 9f53f9fa4ad1 ("libnvdimm, pmem: add libnvdimm support to the pmem > driver") > > "The minor numbers are also more predictable by passing 0 to alloc_disk()." > > How can they possibly be more predictable given that they are allocated > on-demand? Maybe discovery order is very predictable??? > > In any case, I propose this patch but cannot test it (beyond compiling) > as I don't have relevant hardware. And maybe some user-space code greps > /proc/devices for "pmem" to determine if "pmem" is compiled in (though > I sincerely hope not). > So I cannot be certain that this patch won't break anything, but am > hoping that if you like it you might test it. > > If it does prove acceptable, then similar changes would be appropriate > for btt.c and blk.c. And drivers/memstick/core/ms_block.c and > drivers/nvme/host/core.c. (gotta stamp out this cargo cult) > > drivers/lightnvm/core.c is the only driver which uses alloc_disk(0) and > doesn't provide a 'major' number. :-( > > Thanks, > NeilBrown > > > diff --git a/drivers/nvdimm/pmem.c b/drivers/nvdimm/pmem.c > index 8d0b54670184..ec7e9e6a768e 100644 > --- a/drivers/nvdimm/pmem.c > +++ b/drivers/nvdimm/pmem.c > @@ -47,8 +47,6 @@ struct pmem_device { > struct badblocks bb; > }; > > -static int pmem_major; > - > static bool is_bad_pmem(struct badblocks *bb, sector_t sector, unsigned int > len) > { > if (bb->count) { > @@ -228,8 +226,6 @@ static int pmem_attach_disk(struct device *dev, > return -ENOMEM; > } > > - disk->major = pmem_major; > - disk->first_minor = 0; > disk->fops = &pmem_fops; > disk->private_data = pmem; > disk->queue = pmem->pmem_queue; > @@ -502,26 +498,13 @@ static struct nd_device_driver nd_pmem_driver = { > > static int __init pmem_init(void) > { > - int error; > - > - pmem_major = register_blkdev(0, "pmem"); > - if (pmem_major < 0) > - return pmem_major; > - > - error = nd_driver_register(&nd_pmem_driver); > - if (error) { > - unregister_blkdev(pmem_major, "pmem"); > - return error; > - } > - > - return 0; > + return nd_driver_register(&nd_pmem_driver); > } > module_init(pmem_init); > > static void pmem_exit(void) > { > driver_unregister(&nd_pmem_driver.drv); > - unregister_blkdev(pmem_major, "pmem"); > } > module_exit(pmem_exit); > >
