{
  "slug": "fideduperange",
  "term": "FIDEDUPERANGE",
  "aliases": [
    "file range deduplication ioctl"
  ],
  "definition": "FIDEDUPERANGE is a Linux ioctl that compares file ranges and shares their storage when they match.",
  "note": "Unlike cloning, this operation preserves different destination bytes instead of replacing them with source contents. It works within one filesystem and reports status separately for each destination. [fidedupe]\n\nA successful outer call can contain failed or mismatched destinations. In the Linux v6.18 VFS path, a nonnegative callback result is reported using the capped request length, even if generic preparation shortened it. That historical counter is not a byte-accurate coverage certificate or a measurement of reclaimed storage. [dedupe-vfs]\n\nThe Linux v6.12 ioctl wrapper performs work before copying the results back to userspace. Failure of that copy can return EFAULT after work occurred, so an error is not a general rollback guarantee. [dedupe-ioctl]",
  "status": "shipping",
  "advantages": [],
  "limitations": [],
  "related": [
    "reflink",
    "deduplication",
    "copy-on-write",
    "file-extent",
    "btrfs-filesystem-du"
  ],
  "supersedes": [],
  "supersededBy": [],
  "firstSeen": null,
  "lastSeen": null,
  "updated": "2026-10-20",
  "citations": [
    {
      "id": "fidedupe",
      "title": "Linux man-pages: FIDEDUPERANGE, compare-and-share and per-destination results",
      "url": "https://man7.org/linux/man-pages/man2/FIDEDUPERANGE.2const.html",
      "accessed": "2026-10-20"
    },
    {
      "id": "dedupe-vfs",
      "title": "Linux v6.18: remap_range.c, length rounding and historical bytes_deduped reporting",
      "url": "https://raw.githubusercontent.com/torvalds/linux/v6.18/fs/remap_range.c",
      "accessed": "2026-10-20"
    },
    {
      "id": "dedupe-ioctl",
      "title": "Linux v6.12: ioctl.c, FIDEDUPERANGE validation and copying results to userspace",
      "url": "https://raw.githubusercontent.com/torvalds/linux/v6.12/fs/ioctl.c",
      "accessed": "2026-10-20"
    },
    {
      "id": "hesela-clones",
      "title": "Hesela: file cloning and deduplication result accounting",
      "url": "https://hesela.com/analyses/file-clones-deferred-copy-cost/#dedupe",
      "accessed": "2026-10-20"
    }
  ],
  "provenance": [
    "Implementation details refer to the cited upstream tags, not every downstream kernel or the newest release.",
    "The companion worksheet is source-derived arithmetic, not measured filesystem behavior."
  ]
}