[PATCH v3 0/3] ovl: port to new mount api & updated layer parsing

[Christian Brauner <brauner@kernel.org>]

Hey everyone,

/* v3 */
(1) Add a patch that makes sure that struct ovl_layer starts with a
    pointer to struct vfsmount as ovl_free_fs() relies on this during
    cleanup.
(2) Rebase on top of overlayfs-next brought in substantial rework due to
    the data layer work. I had to redo a bunch of the parsing and adapt
    it to the new changes.

This ports overlayfs to the new mount api and modifies layer parsing to
allow for additive layer specification via fsconfig().

This passes xfstests including the new data layer lookup work. Here's a
500 layer overlayfs mount including a couple of data only layers:

1094 28 0:48 / /mnt/test rw,relatime shared:214 - overlay none rw,lowerdir=/mnt/ovl-lower1:/mnt/ovl-lower2:/mnt/ovl-lower3:/mnt/ovl-lower4:/mnt/ovl-lower5:/mnt/ovl-lower6:/mnt/ovl-lower7:/mnt/ovl-lower8:/mnt/ovl-lower9:/mnt/ovl-lower10:/mnt/ovl-lower11:/mnt/ovl-lower12:/mnt/ovl-lower13:/mnt/ovl-lower14:/mnt/ovl-lower15:/mnt/ovl-lower16:/mnt/ovl-lower17:/mnt/ovl-lower18:/mnt/ovl-lower19:/mnt/ovl-lower20:/mnt/ovl-lower21:/mnt/ovl-lower22:/mnt/ovl-lower23:/mnt/ovl-lower24:/mnt/ovl-lower25:/mnt/ovl-lower26:/mnt/ovl-lower27:/mnt/ovl-lower28:/mnt/ovl-lower29:/mnt/ovl-lower30:/mnt/ovl-lower31:/mnt/ovl-lower32:/mnt/ovl-lower33:/mnt/ovl-lower34:/mnt/ovl-lower35:/mnt/ovl-lower36:/mnt/ovl-lower37:/mnt/ovl-lower38:/mnt/ovl-lower39:/mnt/ovl-lower40:/mnt/ovl-lower41:/mnt/ovl-lower42:/mnt/ovl-lower43:/mnt/ovl-lower44:/mnt/ovl-lower45:/mnt/ovl-lower46:/mnt/ovl-lower47:/mnt/ovl-lower48:/mnt/ovl-lower49:/mnt/ovl-lower50:/mnt/ovl-lower51:/mnt/ovl-lower52:/mnt/ovl-lower53:/mnt/ovl-lower54:/mnt/ovl-lower
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 -lower224:/mnt/ovl-lower225:/mnt/ovl-lower226:/mnt/ovl-lower227:/mnt/ovl-lower228:/mnt/ovl-lower229:/mnt/ovl-lower230:/mnt/ovl-lower231:/mnt/ovl-lower232:/mnt/ovl-lower233:/mnt/ovl-lower234:/mnt/ovl-lower235:/mnt/ovl-lower236:/mnt/ovl-lower237:/mnt/ovl-lower238:/mnt/ovl-lower239:/mnt/ovl-lower240:/mnt/ovl-lower241:/mnt/ovl-lower242:/mnt/ovl-lower243:/mnt/ovl-lower244:/mnt/ovl-lower245:/mnt/ovl-lower246:/mnt/ovl-lower247:/mnt/ovl-lower248:/mnt/ovl-lower249:/mnt/ovl-lower250:/mnt/ovl-lower251:/mnt/ovl-lower252:/mnt/ovl-lower253:/mnt/ovl-lower254:/mnt/ovl-lower255:/mnt/ovl-lower256:/mnt/ovl-lower257:/mnt/ovl-lower258:/mnt/ovl-lower259:/mnt/ovl-lower260:/mnt/ovl-lower261:/mnt/ovl-lower262:/mnt/ovl-lower263:/mnt/ovl-lower264:/mnt/ovl-lower265:/mnt/ovl-lower266:/mnt/ovl-lower267:/mnt/ovl-lower268:/mnt/ovl-lower269:/mnt/ovl-lower270:/mnt/ovl-lower271:/mnt/ovl-lower272:/mnt/ovl-lower273:/mnt/ovl-lower274:/mnt/ovl-lower275:/mnt/ovl-lower276:/mnt/ovl-lower277:/mnt/ovl-lower278:/mnt/ovl-lower2
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 /ovl-lower335:/mnt/ovl-lower336:/mnt/ovl-lower337:/mnt/ovl-lower338:/mnt/ovl-lower339:/mnt/ovl-lower340:/mnt/ovl-lower341:/mnt/ovl-lower342:/mnt/ovl-lower343:/mnt/ovl-lower344:/mnt/ovl-lower345:/mnt/ovl-lower346:/mnt/ovl-lower347:/mnt/ovl-lower348:/mnt/ovl-lower349:/mnt/ovl-lower350:/mnt/ovl-lower351:/mnt/ovl-lower352:/mnt/ovl-lower353:/mnt/ovl-lower354:/mnt/ovl-lower355:/mnt/ovl-lower356:/mnt/ovl-lower357:/mnt/ovl-lower358:/mnt/ovl-lower359:/mnt/ovl-lower360:/mnt/ovl-lower361:/mnt/ovl-lower362:/mnt/ovl-lower363:/mnt/ovl-lower364:/mnt/ovl-lower365:/mnt/ovl-lower366:/mnt/ovl-lower367:/mnt/ovl-lower368:/mnt/ovl-lower369:/mnt/ovl-lower370:/mnt/ovl-lower371:/mnt/ovl-lower372:/mnt/ovl-lower373:/mnt/ovl-lower374:/mnt/ovl-lower375:/mnt/ovl-lower376:/mnt/ovl-lower377:/mnt/ovl-lower378:/mnt/ovl-lower379:/mnt/ovl-lower380:/mnt/ovl-lower381:/mnt/ovl-lower382:/mnt/ovl-lower383:/mnt/ovl-lower384:/mnt/ovl-lower385:/mnt/ovl-lower386:/mnt/ovl-lower387:/mnt/ovl-lower388:/mnt/ovl-lower389:/mnt/ovl-lo
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 erdir=/mnt/ovl-upper,workdir=/mnt/ovl-work,redirect_dir=on,index=on,metacopy=on

Christian

Signed-off-by: Christian Brauner <brauner@kernel.org>
---
Changes in v3:
- Fix potential NULL deref in ovl_init_fs_context().
- Don't create one long mount option string for lowerdir. Just use
  seq_printf() to create it on demand.
- Link to v2: https://lore.kernel.org/r/20230605-fs-overlayfs-mount_api-v2-0-3da91c97e0c0@kernel.org

Changes in v2:
- Split into two patches. First patch ports to new mount api without changing
  layer parsing. Second patch implements new layer parsing.
- Move layer parsing into a separate file.
- Link to v1: https://lore.kernel.org/r/20230605-fs-overlayfs-mount_api-v1-1-a8d78c3fbeaf@kernel.org

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base-commit: f777c8266c1230fa44de7261b61a13d787b27f44
change-id: 20230605-fs-overlayfs-mount_api-20ea8b04eff4