Re: [PATCH 08/10] md: Implement ->corrupted_range()

Ruan Shiyang
2021-01-12T12:51:33Z

On 2021/1/7 上午1:14, Jan Kara wrote:
> On Thu 31-12-20 00:55:59, Shiyang Ruan wrote:
>> With the support of ->rmap(), it is possible to obtain the superblock on
>> a mapped device.
>>
>> If a pmem device is used as one target of mapped device, we cannot
>> obtain its superblock directly. With the help of SYSFS, the mapped
>> device can be found on the target devices. So, we iterate the
>> bdev->bd_holder_disks to obtain its mapped device.
>>
>> Signed-off-by: Shiyang Ruan <ruansy.fnst@cn.fujitsu.com>
>
> Thanks for the patch. Two comments below.
>
>> diff --git a/drivers/nvdimm/pmem.c b/drivers/nvdimm/pmem.c
>> index 4688bff19c20..9f9a2f3bf73b 100644
>> --- a/drivers/nvdimm/pmem.c
>> +++ b/drivers/nvdimm/pmem.c
>> @@ -256,21 +256,16 @@ static int pmem_rw_page(struct block_device *bdev, sector_t sector,
>> static int pmem_corrupted_range(struct gendisk *disk, struct block_device *bdev,
>> loff_t disk_offset, size_t len, void *data)
>> {
>> - struct super_block *sb;
>> loff_t bdev_offset;
>> sector_t disk_sector = disk_offset >> SECTOR_SHIFT;
>> - int rc = 0;
>> + int rc = -ENODEV;
>>
>> bdev = bdget_disk_sector(disk, disk_sector);
>> if (!bdev)
>> - return -ENODEV;
>> + return rc;
>>
>> bdev_offset = (disk_sector - get_start_sect(bdev)) << SECTOR_SHIFT;
>> - sb = get_super(bdev);
>> - if (sb && sb->s_op->corrupted_range) {
>> - rc = sb->s_op->corrupted_range(sb, bdev, bdev_offset, len, data);
>> - drop_super(sb);
>> - }
>> + rc = bd_corrupted_range(bdev, bdev_offset, bdev_offset, len, data);
>>
>> bdput(bdev);
>> return rc;
>
> This (and the fs/block_dev.c change below) is just refining the function
> you've implemented in the patch 6. I think it's confusing to split changes
> like this - why not implement things correctly from the start in patch 6?

This change added a helper function to find the md devices created on a
low-level block device, such as a LVM on /dev/pmem0, and calls
->corrupted_range() for each md device. The md parts were introduced
starts from patch 7. So, I add this change in this patch.

>
>> diff --git a/fs/block_dev.c b/fs/block_dev.c
>> index 9e84b1928b94..0e50f0e8e8af 100644
>> --- a/fs/block_dev.c
>> +++ b/fs/block_dev.c
>> @@ -1171,6 +1171,27 @@ struct bd_holder_disk {
>> int refcnt;
>> };
>>
>> +static int bd_disk_holder_corrupted_range(struct block_device *bdev, loff_t off,
>> + size_t len, void *data)
>> +{
>> + struct bd_holder_disk *holder;
>> + struct gendisk *disk;
>> + int rc = 0;
>> +
>> + if (list_empty(&(bdev->bd_holder_disks)))
>> + return -ENODEV;
>
> This will not compile for !CONFIG_SYSFS kernels. Not that it would be
> common but still. Also I'm not sure whether using bd_holder_disks like this
> is really the right thing to do (when it seems to be only a sysfs thing),
> although admittedly I'm not aware of a better way of getting this
> information.

I did a lot of tries and finally found this way. I think I should add a
judgement that whether CONFIG_SYSFS is turned on.

--
Thanks,
Ruan Shiyang.

>
> Honza
>
>> +
>> + list_for_each_entry(holder, &bdev->bd_holder_disks, list) {
>> + disk = holder->disk;
>> + if (disk->fops->corrupted_range) {
>> + rc = disk->fops->corrupted_range(disk, bdev, off, len, data);
>> + if (rc != -ENODEV)
>> + break;
>> + }
>> + }
>> + return rc;
>> +}
>> +
>> static struct bd_holder_disk *bd_find_holder_disk(struct block_device *bdev,
>> struct gendisk *disk)
>> {
>> @@ -1378,6 +1399,22 @@ void bd_set_nr_sectors(struct block_device *bdev, sector_t sectors)
>> }
>> EXPORT_SYMBOL(bd_set_nr_sectors);
>>
>> +int bd_corrupted_range(struct block_device *bdev, loff_t disk_off, loff_t bdev_off, size_t len, void *data)
>> +{
>> + struct super_block *sb = get_super(bdev);
>> + int rc = 0;
>> +
>> + if (!sb) {
>> + rc = bd_disk_holder_corrupted_range(bdev, disk_off, len, data);
>> + return rc;
>> + } else if (sb->s_op->corrupted_range)
>> + rc = sb->s_op->corrupted_range(sb, bdev, bdev_off, len, data);
>> + drop_super(sb);
>> +
>> + return rc;
>> +}
>> +EXPORT_SYMBOL(bd_corrupted_range);
>> +
>> static void __blkdev_put(struct block_device *bdev, fmode_t mode, int for_part);
>>
>> int bdev_disk_changed(struct block_device *bdev, bool invalidate)
>> diff --git a/include/linux/genhd.h b/include/linux/genhd.h
>> index ed06209008b8..42290470810d 100644
>> --- a/include/linux/genhd.h
>> +++ b/include/linux/genhd.h
>> @@ -376,6 +376,8 @@ void revalidate_disk_size(struct gendisk *disk, bool verbose);
>> bool bdev_check_media_change(struct block_device *bdev);
>> int __invalidate_device(struct block_device *bdev, bool kill_dirty);
>> void bd_set_nr_sectors(struct block_device *bdev, sector_t sectors);
>> +int bd_corrupted_range(struct block_device *bdev, loff_t disk_off,
>> + loff_t bdev_off, size_t len, void *data);
>>
>> /* for drivers/char/raw.c: */
>> int blkdev_ioctl(struct block_device *, fmode_t, unsigned, unsigned long);
>> --
>> 2.29.2
>>
>>
>>