kernel/linux.git/Documentation/admin-guide/device-mapper, branch v6.19.11

dm raid: add documentation for takeover/reshape raid1 -> raid5 table line examples

2025-12-10T18:28:22+00:00

Also enhance possible takeover/reshape information and do some reformatting. Signed-off-by: Heinz Mauelshagen Signed-off-by: Mikulas Patocka

dm verity fec: Expose corrected block count via status

2025-11-18T17:24:26+00:00

Enhance visibility into dm-verity Forward Error Correction (FEC) activity. While FEC can correct on-disk corruptions, the number of successful correction events is not readily exposed through a standard interface. This change integrates FEC statistics into the verity target's .status handler for STATUSTYPE_INFO. The info output now includes count of corrected block by FEC. The counter is a per-device instance atomic64_t, maintained within the struct dm_verity_fec, tracking blocks successfully repaired by FEC on this specific device instance since it was created. This approach aligns with the standard Device Mapper mechanism for targets to report runtime information, as used by other targets like dm-integrity. This patch also updates Documentation/admin-guide/device-mapper/verity.rst to reflect the new status information. Tested: Induced single-bit errors on a block device protected by dm-verity with FEC on android phone. Confirmed 'dmctl status ' on Android reports an incrementing 'fec_corrected_blocks' count after the corrupted blocks were accessed. Signed-off-by: Shubhankar Mishra Signed-off-by: Mikulas Patocka

dm-pcache: add persistent cache target in device-mapper

2025-08-25T13:25:29+00:00

This patch introduces dm-pcache, a new DM target that places a DAX- capable persistent-memory device in front of any slower block device and uses it as a high-throughput, low-latency cache. Design highlights ----------------- - DAX data path – data is copied directly between DRAM and the pmem mapping, bypassing the block layer’s overhead. - Segmented, crash-consistent layout - all layout metadata are dual-replicated CRC-protected. - atomic kset flushes; key replay on mount guarantees cache integrity even after power loss. - Striped multi-tree index - Multi‑tree indexing for high parallelism. - overlap-resolution logic ensures non-intersecting cached extents. - Background services - write-back worker flushes dirty keys in order, preserving backing-device crash consistency. This is important for checkpoint in cloud storage. - garbage collector reclaims clean segments when utilisation exceeds a tunable threshold. - Data integrity – optional CRC32 on cached payload; metadata always protected. Comparison with existing block-level caches --------------------------------------------------------------------------------------------------------------------------------- | Feature | pcache (this patch) | bcache | dm-writecache | |----------------------------------|---------------------------------|------------------------------|---------------------------| | pmem access method | DAX | bio (block I/O) | DAX | | Write latency (4 K rand-write) | ~5 µs | ~20 µs | ~5 µs | | Concurrency | multi subtree index | global index tree | single tree + wc_lock | | IOPS (4K randwrite, 32 numjobs) | 2.1 M | 352 K | 283 K | | Read-cache support | YES | YES | NO | | Deployment | no re-format of backend | backend devices must be | no re-format of backend | | | | reformatted | | | Write-back ordering | log-structured; | no ordering guarantee | no ordering guarantee | | | preserves app-IO-order | | | | Data integrity checks | metadata + data CRC(optional) | metadata CRC only | none | --------------------------------------------------------------------------------------------------------------------------------- Signed-off-by: Dongsheng Yang Signed-off-by: Mikulas Patocka

dm-vdo: Promote dm-vdo title to title heading

2025-08-19T09:12:50+00:00

dm-vdo docs currently has no explicit title heading but instead there are multiple section headings as top-level heading. As such, these sections are rendered as titles and inflates number of entries in the toctree index. Promote the first section heading ("dm-vdo") to title heading. Fixes: 04bf7ac646ab ("dm: add documentation for dm-vdo target") Signed-off-by: Bagas Sanjaya Signed-off-by: Mikulas Patocka

docs: device-mapper: fixed spelling mistakes in documentation

2025-08-19T09:12:50+00:00

found/fixed the following typos - flushs -> flushes in `Documentation/admin-guide/device-mapper/delay.rst` Signed-off-by: Soham Metha Signed-off-by: Mikulas Patocka

docs: device-mapper: fix typos in delay.rst and vdo-design.rst

2025-08-19T09:12:49+00:00

Fixed the following typos in device-mapper documentation: - explicitely -> explicitly - approriate -> appropriate Signed-off-by: Shubham Sharma Signed-off-by: Mikulas Patocka

dm-thin: update the documentation

2025-07-31T13:43:30+00:00

1. convert KB/MB/GB to KiB/MiB/GiB; 2. change the number of sectors for 128MiB from 256000 to 262144 as 256000 sectors is neither 128 MB nor 128 MiB. Signed-off-by: LongPing Wei Signed-off-by: Mikulas Patocka

dm-verity: support block number limits for different ioprio classes

2025-03-28T10:32:55+00:00

Calling verity_verify_io in bh for IO of all sizes is not suitable for embedded devices. From our tests, it can improve the performance of 4K synchronise random reads. For example: ./fio --name=rand_read --ioengine=psync --rw=randread --bs=4K \ --direct=1 --numjobs=8 --runtime=60 --time_based --group_reporting \ --filename=/dev/block/mapper/xx-verity But it will degrade the performance of 512K synchronise sequential reads on our devices. For example: ./fio --name=read --ioengine=psync --rw=read --bs=512K --direct=1 \ --numjobs=8 --runtime=60 --time_based --group_reporting \ --filename=/dev/block/mapper/xx-verity A parameter array is introduced by this change. And users can modify the default config by /sys/module/dm_verity/parameters/use_bh_bytes. The default limits for NONE/RT/BE is set to 8192. The default limits for IDLE is set to 0. Call verity_verify_io directly when verity_end_io is not in hardirq. Signed-off-by: LongPing Wei Signed-off-by: Mikulas Patocka

dm-crypt: Document integrity_key_size option.

2025-02-03T13:10:10+00:00

This patch adds documentation for new option introduced in commit 4441686b24a1 ("dm-crypt: Allow to specify the integrity key size as option"). Signed-off-by: Milan Broz Signed-off-by: Mikulas Patocka

dm-integrity: Document Inline mode for storing integrity data

2025-02-03T13:10:10+00:00

This patch adds documentation for new 'I' mode for dm-integrity introduced in commit fb0987682c62 ("dm-integrity: introduce the Inline mode"). Signed-off-by: Milan Broz Signed-off-by: Mikulas Patocka