Merge tag 'erofs-for-5.19-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/xiang/erofs

Pull erofs (and fscache) updates from Gao Xiang:
 "After working on it on the mailing list for more than half a year, we
  finally form 'erofs over fscache' feature into shape. Hopefully it
  could bring more possibility to the communities.

  The story mainly started from a new project what we called "RAFS v6" [1]
  for Nydus image service almost a year ago, which enhances EROFS to be
  a new form of one bootstrap (which includes metadata representing the
  whole fs tree) + several data-deduplicated content addressable blobs
  (actually treated as multiple devices). Each blob can represent one
  container image layer but not quite exactly since all new data can be
  fully existed in the previous blobs so no need to introduce another
  new blob.

  It is actually not a new idea (at least on my side it's much like a
  simpilied casync [2] for now) and has many benefits over per-file
  blobs or some other exist ways since typically each RAFS v6 image only
  has dozens of device blobs instead of thousands of per-file blobs.
  It's easy to be signed with user keys as a golden image, transfered
  untouchedly with minimal overhead over the network, kept in some type
  of storage conveniently, and run with (optional) runtime verification
  but without involving too many irrelevant features crossing the system
  beyond EROFS itself. At least it's our final goal and we're keeping
  working on it. There was also a good summary of this approach from the
  casync author [3].

  Regardless further optimizations, this work is almost done in the
  previous Linux release cycles. In this round, we'd like to introduce
  on-demand load for EROFS with the fscache/cachefiles infrastructure,
  considering the following advantages:

   - Introduce new file-based backend to EROFS. Although each image only
     contains dozens of blobs but in densely-deployed runC host for
     example, there could still be massive blobs on a machine, which is
     messy if each blob is treated as a device. In contrast, fscache and
     cachefiles are really great interfaces for us to make them work.

   - Introduce on-demand load to fscache and EROFS. Previously, fscache
     is mainly used to caching network-likewise filesystems, now it can
     support on-demand downloading for local fses too with the exact
     localfs on-disk format. It has many advantages which we're been
     described in the latest patchset cover letter [4]. In addition to
     that, most importantly, the cached data is still stored in the
     original local fs on-disk format so that it's still the one signed
     with private keys but only could be partially available. Users can
     fully trust it during running. Later, users can also back up
     cachefiles easily to another machine.

   - More reliable on-demand approach in principle. After data is all
     available locally, user daemon can be no longer online in some use
     cases, which helps daemon crash recovery (filesystems can still in
     service) and hot-upgrade (user daemon can be upgraded more
     frequently due to new features or protocols introduced.)

   - Other format can also be converted to EROFS filesystem format over
     the internet on the fly with the new on-demand load feature and
     mounted. That is entirely possible with on-demand load feature as
     long as such archive format metadata can be fetched in advance like
     stargz.

  In addition, although currently our target user is Nydus image service [5],
  but laterly, it can be used for other use cases like on-demand system
  booting, etc. As for the fscache on-demand load feature itself,
  strictly it can be used for other local fses too. Laterly we could
  promote most code to the iomap infrastructure and also enhance it in
  the read-write way if other local fses are interested.

  Thanks David Howells for taking so much time and patience on this
  these months, many thanks with great respect here again! Thanks Jeffle
  for working on this feature and Xin Yin from Bytedance for
  asynchronous I/O implementation as well as Zichen Tian, Jia Zhu, and
  Yan Song for testing, much appeciated. We're also exploring more
  possibly over fscache cache management over FSDAX for secure
  containers and working on more improvements and useful features for
  fscache, cachefiles, and on-demand load.

  In addition to "erofs over fscache", NFS export and idmapped mount are
  also completed in this cycle for container use cases as well.

  Summary:

   - Add erofs on-demand load support over fscache

   - Support NFS export for erofs

   - Support idmapped mounts for erofs

   - Don't prompt for risk any more when using big pcluster

   - Fix buffer copy overflow of ztailpacking feature

   - Several minor cleanups"

[1] https://lore.kernel.org/r/20210730194625.93856-1-hsiangkao@linux.alibaba.com
[2] https://github.com/systemd/casync
[3] http://0pointer.net/blog/casync-a-tool-for-distributing-file-system-images.html
[4] https://lore.kernel.org/r/20220509074028.74954-1-jefflexu@linux.alibaba.com
[5] https://github.com/dragonflyoss/image-service

* tag 'erofs-for-5.19-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/xiang/erofs: (29 commits)
  erofs: scan devices from device table
  erofs: change to use asynchronous io for fscache readpage/readahead
  erofs: add 'fsid' mount option
  erofs: implement fscache-based data readahead
  erofs: implement fscache-based data read for inline layout
  erofs: implement fscache-based data read for non-inline layout
  erofs: implement fscache-based metadata read
  erofs: register fscache context for extra data blobs
  erofs: register fscache context for primary data blob
  erofs: add erofs_fscache_read_folios() helper
  erofs: add anonymous inode caching metadata for data blobs
  erofs: add fscache context helper functions
  erofs: register fscache volume
  erofs: add fscache mode check helper
  erofs: make erofs_map_blocks() generally available
  cachefiles: document on-demand read mode
  cachefiles: add tracepoints for on-demand read mode
  cachefiles: enable on-demand read mode
  cachefiles: implement on-demand read
  cachefiles: notify the user daemon when withdrawing cookie
  ...

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