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)
>
> Changes to v3:
> * make flags in/out (David)
> * make csum return opt-in (Hans)
>
> Changes to v2:
> * add additional csum_size (David)
> * rename flag value to BTRFS_FS_INFO_FLAG_CSUM_TYPE_SIZE to reflect
> additional size
>
> Changes to v1:
> * add 'out' comment to be consistent (Hans)
> * remove le16_to_cpu() (kbuild robot)
> * switch padding to be all u8 (David)
> ---
> fs/btrfs/ioctl.c | 16 +++++++++++++---
> include/uapi/linux/btrfs.h | 14 ++++++++++++--
> 2 files changed, 25 insertions(+), 5 deletions(-)
>
> diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
> index ab34179d7cbc..df8a6ba91055 100644
> --- a/fs/btrfs/ioctl.c
> +++ b/fs/btrfs/ioctl.c
> @@ -3217,11 +3217,15 @@ static long btrfs_ioctl_fs_info(struct btrfs_fs_info *fs_info,
> struct btrfs_ioctl_fs_info_args *fi_args;
> struct btrfs_device *device;
> struct btrfs_fs_devices *fs_devices = fs_info->fs_devices;
> + u32 inflags;
> int ret = 0;
>
> - fi_args = kzalloc(sizeof(*fi_args), GFP_KERNEL);
> - if (!fi_args)
> - return -ENOMEM;
> + fi_args = memdup_user(arg, sizeof(*fi_args));
> + if (IS_ERR(fi_args))
> + return PTR_ERR(fi_args);
> +
> + inflags = fi_args->flags;
> + memset(fi_args, 0, sizeof(*fi_args));
>
> rcu_read_lock();
> fi_args->num_devices = fs_devices->num_devices;
> @@ -3237,6 +3241,12 @@ static long btrfs_ioctl_fs_info(struct btrfs_fs_info *fs_info,
> fi_args->sectorsize = fs_info->sectorsize;
> fi_args->clone_alignment = fs_info->sectorsize;
>
> + if (inflags & BTRFS_FS_INFO_FLAG_CSUM_TYPE_SIZE) {
> + fi_args->csum_type = btrfs_super_csum_type(fs_info->super_copy);
> + fi_args->csum_size = btrfs_super_csum_size(fs_info->super_copy);
> + fi_args->flags |= BTRFS_FS_INFO_FLAG_CSUM_TYPE_SIZE;
> + }
That's safe, but we'll have to add a new flag for all new members and we
have already 2 ready (generation, metadata_uuid) and ioctl user has to
set the bits. Minor inconvenience, in exchange for future extensions, so
let it be.
> +
> if (copy_to_user(arg, fi_args, sizeof(*fi_args)))
> ret = -EFAULT;
>
> diff --git a/include/uapi/linux/btrfs.h b/include/uapi/linux/btrfs.h
> index e6b6cb0f8bc6..c130eaea416e 100644
> --- a/include/uapi/linux/btrfs.h
> +++ b/include/uapi/linux/btrfs.h
> @@ -250,10 +250,20 @@ struct btrfs_ioctl_fs_info_args {
> __u32 nodesize; /* out */
> __u32 sectorsize; /* out */
> __u32 clone_alignment; /* out */
> - __u32 reserved32;
> - __u64 reserved[122]; /* pad to 1k */
> + __u32 flags; /* in/out */
> + __u16 csum_type; /* out */
> + __u16 csum_size; /* out */
> + __u8 reserved[972]; /* pad to 1k */
> };
>
> +/*
> + * fs_info ioctl flags
> + *
> + * Used by:
> + * struct btrfs_ioctl_fs_info_args
> + */
> +#define BTRFS_FS_INFO_FLAG_CSUM_TYPE_SIZE (1 << 0)
Flags should be defined before the structure, but that I can fix up.
