From 794ca29dcc924cd3f16d12b6fba61074c992b8fd Mon Sep 17 00:00:00 2001 From: John Garry Date: Mon, 3 Mar 2025 17:11:13 +0000 Subject: iomap: Support SW-based atomic writes Currently atomic write support requires dedicated HW support. This imposes a restriction on the filesystem that disk blocks need to be aligned and contiguously mapped to FS blocks to issue atomic writes. XFS has no method to guarantee FS block alignment for regular, non-RT files. As such, atomic writes are currently limited to 1x FS block there. To deal with the scenario that we are issuing an atomic write over misaligned or discontiguous data blocks - and raise the atomic write size limit - support a SW-based software emulated atomic write mode. For XFS, this SW-based atomic writes would use CoW support to issue emulated untorn writes. It is the responsibility of the FS to detect discontiguous atomic writes and switch to IOMAP_DIO_ATOMIC_SW mode and retry the write. Indeed, SW-based atomic writes could be used always when the mounted bdev does not support HW offload, but this strategy is not initially expected to be used. Reviewed-by: "Darrick J. Wong" Signed-off-by: John Garry Link: https://lore.kernel.org/r/20250303171120.2837067-6-john.g.garry@oracle.com Signed-off-by: Christian Brauner --- include/linux/iomap.h | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) (limited to 'include/linux') diff --git a/include/linux/iomap.h b/include/linux/iomap.h index 87cd7079aaf3..9cd93530013c 100644 --- a/include/linux/iomap.h +++ b/include/linux/iomap.h @@ -189,8 +189,9 @@ struct iomap_folio_ops { #else #define IOMAP_DAX 0 #endif /* CONFIG_FS_DAX */ -#define IOMAP_ATOMIC_HW (1 << 9) +#define IOMAP_ATOMIC_HW (1 << 9) /* HW-based torn-write protection */ #define IOMAP_DONTCACHE (1 << 10) +#define IOMAP_ATOMIC_SW (1 << 11)/* SW-based torn-write protection */ struct iomap_ops { /* @@ -502,6 +503,11 @@ struct iomap_dio_ops { */ #define IOMAP_DIO_PARTIAL (1 << 2) +/* + * Use software-based torn-write protection. + */ +#define IOMAP_DIO_ATOMIC_SW (1 << 3) + ssize_t iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter, const struct iomap_ops *ops, const struct iomap_dio_ops *dops, unsigned int dio_flags, void *private, size_t done_before); -- cgit v1.2.3