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@vger.kernel.org # 5.5+ Signed-off-by: Johannes Thumshirn johannes.thumshirn@wdc.com
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.