On Mon, Feb 03, 2025 at 10:43:11AM +0100, Christoph Hellwig wrote:
> This is a quick hack to demonstrate how data checksumming can be
> implemented when it can be stored in the out of line metadata for each
> logical block. It builds on top of the previous PI infrastructure
> and instead of generating/verifying protection information it simply
> generates and verifies a crc32c checksum and stores it in the non-PI
PI can do crc32c now? I thought it could only do that old crc16 from
like 15 years ago and crc64? If we try to throw crc32c at a device,
won't it then reject the "incorrect" checksums? Or is there some other
magic in here where it works and I'm just too out of date to know?
<shrug>
The crc32c generation and validation looks decent though we're
definitely going to want an inode flag so that we're not stuck with
stable page writes.
--D
> metadata. It misses a feature bit in the superblock, checking that
> enough size is available in the metadata and many other things.
>
> Signed-off-by: Christoph Hellwig <hch@xxxxxx>
> ---
> fs/xfs/xfs_data_csum.c | 79 ++++++++++++++++++++++++++++++++++++++++--
> 1 file changed, 76 insertions(+), 3 deletions(-)
>
> diff --git a/fs/xfs/xfs_data_csum.c b/fs/xfs/xfs_data_csum.c
> index d9d3620654b1..862388803398 100644
> --- a/fs/xfs/xfs_data_csum.c
> +++ b/fs/xfs/xfs_data_csum.c
> @@ -14,6 +14,73 @@
> #include <linux/blk-integrity.h>
> #include <linux/bio-integrity.h>
>
> +static inline void *xfs_csum_buf(struct bio *bio)
> +{
> + return bvec_virt(bio_integrity(bio)->bip_vec);
> +}
> +
> +static inline __le32
> +xfs_data_csum(
> + void *data,
> + unsigned int len)
> +{
> + return xfs_end_cksum(crc32c(XFS_CRC_SEED, data, len));
> +}
> +
> +static void
> +__xfs_data_csum_generate(
> + struct bio *bio)
> +{
> + unsigned int ssize = bdev_logical_block_size(bio->bi_bdev);
> + __le32 *csum_buf = xfs_csum_buf(bio);
> + struct bvec_iter_all iter;
> + struct bio_vec *bv;
> + int c = 0;
> +
> + bio_for_each_segment_all(bv, bio, iter) {
> + void *p;
> + unsigned int off;
> +
> + p = bvec_kmap_local(bv);
> + for (off = 0; off < bv->bv_len; off += ssize)
> + csum_buf[c++] = xfs_data_csum(p + off, ssize);
> + kunmap_local(p);
> + }
> +}
> +
> +static int
> +__xfs_data_csum_verify(
> + struct bio *bio,
> + struct xfs_inode *ip,
> + xfs_off_t file_offset)
> +{
> + unsigned int ssize = bdev_logical_block_size(bio->bi_bdev);
> + __le32 *csum_buf = xfs_csum_buf(bio);
> + int c = 0;
> + struct bvec_iter_all iter;
> + struct bio_vec *bv;
> +
> + bio_for_each_segment_all(bv, bio, iter) {
> + void *p;
> + unsigned int off;
> +
> + p = bvec_kmap_local(bv);
> + for (off = 0; off < bv->bv_len; off += ssize) {
> + if (xfs_data_csum(p + off, ssize) != csum_buf[c++]) {
> + kunmap_local(p);
> + xfs_warn(ip->i_mount,
> +"checksum mismatch at inode 0x%llx offset %lld",
> + ip->i_ino, file_offset);
> + return -EFSBADCRC;
> + }
> + file_offset += ssize;
> + }
> + kunmap_local(p);
> + }
> +
> + return 0;
> +}
> +
> void *
> xfs_data_csum_alloc(
> struct bio *bio)
> @@ -53,11 +120,14 @@ xfs_data_csum_generate(
> {
> struct blk_integrity *bi = blk_get_integrity(bio->bi_bdev->bd_disk);
>
> - if (!bi || !bi->csum_type)
> + if (!bi)
> return;
>
> xfs_data_csum_alloc(bio);
> - blk_integrity_generate(bio);
> + if (!bi->csum_type)
> + __xfs_data_csum_generate(bio);
> + else
> + blk_integrity_generate(bio);
> }
>
> int
> @@ -67,7 +137,10 @@ xfs_data_csum_verify(
> struct bio *bio = &ioend->io_bio;
> struct blk_integrity *bi = blk_get_integrity(bio->bi_bdev->bd_disk);
>
> - if (!bi || !bi->csum_type)
> + if (!bi)
> return 0;
> + if (!bi->csum_type)
> + return __xfs_data_csum_verify(&ioend->io_bio,
> + XFS_I(ioend->io_inode), ioend->io_offset);
> return blk_integrity_verify_all(bio, ioend->io_sector);
> }
> --
> 2.45.2
>
>
