Introduce segment.{c,h}, an internal abstraction that encapsulates
everything related to a single pcache *segment* (the fixed-size
allocation unit stored on the cache-device).
* On-disk metadata (`struct pcache_segment_info`)
- Embedded `struct pcache_meta_header` for CRC/sequence handling.
- `flags` field encodes a “has-next” bit and a 4-bit *type* class
(`CACHE_DATA` added as the first type).
* Initialisation
- `pcache_segment_init()` populates the in-memory
`struct pcache_segment` from a given segment id, data offset and
metadata pointer, computing the usable `data_size` and virtual
address within the DAX mapping.
* IO helpers
- `segment_copy_to_bio()` / `segment_copy_from_bio()` move data
between pmem and a bio, using `_copy_mc_to_iter()` and
`_copy_from_iter_flushcache()` to tolerate hw memory errors and
ensure durability.
- `segment_pos_advance()` advances an internal offset while staying
inside the segment’s data area.
These helpers allow upper layers (cache key management, write-back
logic, GC, etc.) to treat a segment as a contiguous byte array without
knowing about DAX mappings or persistence details.
Signed-off-by: Dongsheng Yang <dongsheng.y...@linux.dev>
---
drivers/md/dm-pcache/segment.c | 61 ++++++++++++++++++++++++++++
drivers/md/dm-pcache/segment.h | 74 ++++++++++++++++++++++++++++++++++
2 files changed, 135 insertions(+)
create mode 100644 drivers/md/dm-pcache/segment.c
create mode 100644 drivers/md/dm-pcache/segment.h
diff --git a/drivers/md/dm-pcache/segment.c b/drivers/md/dm-pcache/segment.c
new file mode 100644
index 000000000000..7e9818701445
--- /dev/null
+++ b/drivers/md/dm-pcache/segment.c
@@ -0,0 +1,61 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+#include <linux/dax.h>
+
+#include "pcache_internal.h"
+#include "cache_dev.h"
+#include "segment.h"
+
+int segment_copy_to_bio(struct pcache_segment *segment,
+ u32 data_off, u32 data_len, struct bio *bio, u32 bio_off)
+{
+ struct iov_iter iter;
+ size_t copied;
+ void *src;
+
+ iov_iter_bvec(&iter, ITER_DEST, &bio->bi_io_vec[bio->bi_iter.bi_idx],
+ bio_segments(bio), bio->bi_iter.bi_size);
+ iter.iov_offset = bio->bi_iter.bi_bvec_done;
+ if (bio_off)
+ iov_iter_advance(&iter, bio_off);
+
+ src = segment->data + data_off;
+ copied = _copy_mc_to_iter(src, data_len, &iter);
+ if (copied != data_len)
+ return -EIO;
+
+ return 0;
+}
+
+int segment_copy_from_bio(struct pcache_segment *segment,
+ u32 data_off, u32 data_len, struct bio *bio, u32 bio_off)
+{
+ struct iov_iter iter;
+ size_t copied;
+ void *dst;
+
+ iov_iter_bvec(&iter, ITER_SOURCE, &bio->bi_io_vec[bio->bi_iter.bi_idx],
+ bio_segments(bio), bio->bi_iter.bi_size);
+ iter.iov_offset = bio->bi_iter.bi_bvec_done;
+ if (bio_off)
+ iov_iter_advance(&iter, bio_off);
+
+ dst = segment->data + data_off;
+ copied = _copy_from_iter_flushcache(dst, data_len, &iter);
+ if (copied != data_len)
+ return -EIO;
+ pmem_wmb();
+
+ return 0;
+}
+
+void pcache_segment_init(struct pcache_cache_dev *cache_dev, struct
pcache_segment *segment,
+ struct pcache_segment_init_options *options)
+{
+ segment->seg_info = options->seg_info;
+ segment_info_set_type(segment->seg_info, options->type);
+
+ segment->cache_dev = cache_dev;
+ segment->seg_id = options->seg_id;
+ segment->data_size = PCACHE_SEG_SIZE - options->data_off;
+ segment->data = CACHE_DEV_SEGMENT(cache_dev, options->seg_id) +
options->data_off;
+}
diff --git a/drivers/md/dm-pcache/segment.h b/drivers/md/dm-pcache/segment.h
new file mode 100644
index 000000000000..deca1ddcb02b
--- /dev/null
+++ b/drivers/md/dm-pcache/segment.h
@@ -0,0 +1,74 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+#ifndef _PCACHE_SEGMENT_H
+#define _PCACHE_SEGMENT_H
+
+#include <linux/bio.h>
+#include <linux/bitfield.h>
+
+#include "pcache_internal.h"
+
+struct pcache_segment_info {
+ struct pcache_meta_header header;
+ __u32 flags;
+ __u32 next_seg;
+};
+
+#define PCACHE_SEG_INFO_FLAGS_HAS_NEXT BIT(0)
+
+#define PCACHE_SEG_INFO_FLAGS_TYPE_MASK GENMASK(4, 1)
+#define PCACHE_SEGMENT_TYPE_CACHE_DATA 1
+
+static inline bool segment_info_has_next(struct pcache_segment_info *seg_info)
+{
+ return (seg_info->flags & PCACHE_SEG_INFO_FLAGS_HAS_NEXT);
+}
+
+static inline void segment_info_set_type(struct pcache_segment_info *seg_info,
u8 type)
+{
+ seg_info->flags &= ~PCACHE_SEG_INFO_FLAGS_TYPE_MASK;
+ seg_info->flags |= FIELD_PREP(PCACHE_SEG_INFO_FLAGS_TYPE_MASK, type);
+}
+
+static inline u8 segment_info_get_type(struct pcache_segment_info *seg_info)
+{
+ return FIELD_GET(PCACHE_SEG_INFO_FLAGS_TYPE_MASK, seg_info->flags);
+}
+
+struct pcache_segment_pos {
+ struct pcache_segment *segment; /* Segment associated with the
position */
+ u32 off; /* Offset within the segment */
+};
+
+struct pcache_segment_init_options {
+ u8 type;
+ u32 seg_id;
+ u32 data_off;
+
+ struct pcache_segment_info *seg_info;
+};
+
+struct pcache_segment {
+ struct pcache_cache_dev *cache_dev;
+
+ void *data;
+ u32 data_size;
+ u32 seg_id;
+
+ struct pcache_segment_info *seg_info;
+};
+
+int segment_copy_to_bio(struct pcache_segment *segment,
+ u32 data_off, u32 data_len, struct bio *bio, u32 bio_off);
+int segment_copy_from_bio(struct pcache_segment *segment,
+ u32 data_off, u32 data_len, struct bio *bio, u32
bio_off);
+
+static inline void segment_pos_advance(struct pcache_segment_pos *seg_pos, u32
len)
+{
+ BUG_ON(seg_pos->off + len > seg_pos->segment->data_size);
+
+ seg_pos->off += len;
+}
+
+void pcache_segment_init(struct pcache_cache_dev *cache_dev, struct
pcache_segment *segment,
+ struct pcache_segment_init_options *options);
+#endif /* _PCACHE_SEGMENT_H */
--
2.43.0
