On Tue, Jul 07, 2020 at 12:09:24AM +0900, Johannes Thumshirn wrote:
> With the recent addition of filesystem checksum types other than CRC32c,
> it is not anymore hard-coded which checksum type a btrfs filesystem uses.
>
> Up to now there is no good way to read the filesystem checksum, apart from
> reading the filesystem UUID and then query sysfs for the checksum type.
>
> Add a new csum_type and csum_size fields to the BTRFS_IOC_FS_INFO ioctl
> command which usually is used to query filesystem features. Also add a
> flags member indicating that the kernel responded with a set csum_type and
> csum_size field.
>
> For compatibility reasons, only return the csum_type and csum_size if the
> BTRFS_FS_INFO_FLAG_CSUM_TYPE_SIZE flag was passed to the kernel. Also
> clear any unknown flags so we don't pass false positives to user-space
> newer than the kernel.
>
> To simplify further additions to the ioctl, also switch the padding to a
> u8 array. Pahole was used to verify the result of this switch:
>
> pahole -C btrfs_ioctl_fs_info_args fs/btrfs/btrfs.ko
> struct btrfs_ioctl_fs_info_args {
> __u64 max_id; /* 0 8 */
> __u64 num_devices; /* 8 8 */
> __u8 fsid[16]; /* 16 16 */
> __u32 nodesize; /* 32 4 */
> __u32 sectorsize; /* 36 4 */
> __u32 clone_alignment; /* 40 4 */
> __u32 flags; /* 44 4 */
> __u16 csum_type; /* 48 2 */
> __u16 csum_size; /* 50 2 */
> __u8 reserved[972]; /* 52 972 */
>
> /* size: 1024, cachelines: 16, members: 10 */
> };
>
> Fixes: 3951e7f050ac ("btrfs: add xxhash64 to checksumming algorithms")
> Fixes: 3831bf0094ab ("btrfs: add sha256 to checksumming algorithm")
> CC: stable@xxxxxxxxxxxxxxx # 5.5+
> Signed-off-by: Johannes Thumshirn <johannes.thumshirn@xxxxxxx>
> ---
> Changes to v4:
> * zero all data passed in from user-space
> (I've chosen this variant as I think it is the most complete)
I'll have to refresh the whole evolution since v1 but the memset sounds
reasonable to me.
