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Re: [PATCH v11 21/48] ext4: Add richacl feature flag

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On Fri, Oct 16, 2015 at 02:27:57PM -0400, Austin S Hemmelgarn wrote:
> On 2015-10-16 13:41, Andreas Gruenbacher wrote:
> >On Fri, Oct 16, 2015 at 7:31 PM, Austin S Hemmelgarn
> ><ahferroin7@gmail.com> wrote:
> >>I would like to re-iterate, on both XFS and ext4, I _really_ think this
> >>should be a ro_compat flag, and not an incompat one.  If a person has the
> >>ability to mount the FS (even if it's a read-only mount), then they by
> >>definition have read access to the file or partition that the filesystem is
> >>contained in, which means that any ACL's stored on the filesystem are
> >>functionally irrelevant,
> >
> >It is unfortunately not safe to make such a file system accessible to
> >other users, so the feature is not strictly read-only compatible.
> If it's not safe WRT data integrity, then the design needs to be
> reworked, as that directly implies that isn't safe for even every
> day usage on a writable filesystem.

This is exactly what we have *incompat feature flags for*: to
protect old code that doesn't know about potentially dangerous new
on-disk formats from trying to parse those formats and causing
unpredictable bad things from happening.

Austin, your arguments hold no weight because they are no different
to the considerations for any new on-disk feature: the user needs to
have both kernel and userspace support to recover filesystems that
go bad. If you are using a brand new fs/kernel feature, then it is
expected that you know that your DR processes take this into
account.

This is also why we XFS devs wait at least a year after new on-disk
features are merged into XFS before we consider turning them on by
default. i.e.  to give distros and recovery utilities time to pick
up kernels and userspace pacakges that support the new feature
before the average user will encounter it....

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com
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[PATCH v11 00/48] Richacls Andreas Gruenbacher <agruenba@redhat.com> - 2015-10-16 17:20 +0200
  [PATCH v11 10/48] vfs: Cache base_acl objects in inodes Andreas Gruenbacher <agruenba@redhat.com> - 2015-10-16 17:20 +0200
  [PATCH v11 04/48] vfs: Make the inode passed to inode_change_ok non-const Andreas Gruenbacher <agruenba@redhat.com> - 2015-10-16 17:20 +0200
  [PATCH v11 11/48] vfs: Add get_richacl and set_richacl inode operations Andreas Gruenbacher <agruenba@redhat.com> - 2015-10-16 17:20 +0200
  [PATCH v11 05/48] vfs: Add permission flags for setting file attributes Andreas Gruenbacher <agruenba@redhat.com> - 2015-10-16 17:20 +0200
  [PATCH v11 06/48] richacl: In-memory representation and helper functions Andreas Gruenbacher <agruenba@redhat.com> - 2015-10-16 17:20 +0200
  [PATCH v11 01/48] vfs: Add IS_ACL() and IS_RICHACL() tests Andreas Gruenbacher <agruenba@redhat.com> - 2015-10-16 17:20 +0200
  [PATCH v11 03/48] vfs: Add MAY_DELETE_SELF and MAY_DELETE_CHILD permission flags Andreas Gruenbacher <agruenba@redhat.com> - 2015-10-16 17:20 +0200
  [PATCH v11 41/48] xfs: Don't allow unmapped identifiers in richacls Andreas Gruenbacher <agruenba@redhat.com> - 2015-10-16 17:30 +0200
  [PATCH v11 39/48] nfsd: Add support for unmapped richace identifiers Andreas Gruenbacher <agruenba@redhat.com> - 2015-10-16 17:30 +0200
  [PATCH v11 25/48] richacl: acl editing helper functions Andreas Gruenbacher <agruenba@redhat.com> - 2015-10-16 17:30 +0200
  [PATCH v11 22/48] xfs: Fix error path in xfs_get_acl Andreas Gruenbacher <agruenba@redhat.com> - 2015-10-16 17:30 +0200
  [PATCH v11 46/48] nfs: Distinguish missing users and groups from nobody Andreas Gruenbacher <agruenba@redhat.com> - 2015-10-16 17:30 +0200
  [PATCH v11 42/48] sunrpc: Allow to demand-allocate pages to encode into Andreas Gruenbacher <agruenba@redhat.com> - 2015-10-16 17:30 +0200
  [PATCH v11 31/48] richacl: Apply the file masks to a richacl Andreas Gruenbacher <agruenba@redhat.com> - 2015-10-16 17:30 +0200
  [PATCH v11 29/48] richacl: Set the other permissions to the other mask Andreas Gruenbacher <agruenba@redhat.com> - 2015-10-16 17:30 +0200
  [PATCH v11 38/48] richacl: Add support for unmapped identifiers Andreas Gruenbacher <agruenba@redhat.com> - 2015-10-16 17:30 +0200
  [PATCH v11 48/48] nfs: Add support for the v4.1 dacl attribute Andreas Gruenbacher <agruenba@redhat.com> - 2015-10-16 17:30 +0200
  [PATCH v11 24/48] xfs: Add richacl support Andreas Gruenbacher <agruenba@redhat.com> - 2015-10-16 17:30 +0200
  [PATCH v11 45/48] nfs: Remove unused xdr page offsets in getacl/setacl arguments Andreas Gruenbacher <agruenba@redhat.com> - 2015-10-16 17:30 +0200
  [PATCH v11 47/48] nfs: Add richacl support Andreas Gruenbacher <agruenba@redhat.com> - 2015-10-16 17:30 +0200
  [PATCH v11 12/48] vfs: Cache richacl in struct inode Andreas Gruenbacher <agruenba@redhat.com> - 2015-10-16 17:30 +0200
  [PATCH v11 19/48] vfs: Add richacl permission checking Andreas Gruenbacher <agruenba@redhat.com> - 2015-10-16 17:30 +0200
  [PATCH v11 23/48] xfs: Make xfs_set_mode non-static Andreas Gruenbacher <agruenba@redhat.com> - 2015-10-16 17:30 +0200
  [PATCH v11 21/48] ext4: Add richacl feature flag Andreas Gruenbacher <agruenba@redhat.com> - 2015-10-16 17:30 +0200
    Re: [PATCH v11 21/48] ext4: Add richacl feature flag Austin S Hemmelgarn <ahferroin7@gmail.com> - 2015-10-16 19:40 +0200
      Re: [PATCH v11 21/48] ext4: Add richacl feature flag Andreas Gruenbacher <agruenba@redhat.com> - 2015-10-16 19:50 +0200
        Re: [PATCH v11 21/48] ext4: Add richacl feature flag Austin S Hemmelgarn <ahferroin7@gmail.com> - 2015-10-16 20:30 +0200
          Re: [PATCH v11 21/48] ext4: Add richacl feature flag Dave Chinner <david@fromorbit.com> - 2015-10-18 01:30 +0200
  [PATCH v11 44/48] nfs: Fix GETATTR bitmap verification Andreas Gruenbacher <agruenba@redhat.com> - 2015-10-16 17:30 +0200
  [PATCH v11 37/48] nfsd: Add support for the MAY_CREATE_{FILE,DIR} permissions Andreas Gruenbacher <agruenba@redhat.com> - 2015-10-16 17:30 +0200
  [PATCH v11 16/48] richacl: Automatic Inheritance Andreas Gruenbacher <agruenba@redhat.com> - 2015-10-16 17:30 +0200
    Re: [PATCH v11 16/48] richacl: Automatic Inheritance Andy Lutomirski <luto@amacapital.net> - 2015-10-16 18:10 +0200
      Re: [PATCH v11 16/48] richacl: Automatic Inheritance Andreas Gruenbacher <agruenba@redhat.com> - 2015-10-16 18:20 +0200
  [PATCH v11 18/48] richacl: Add richacl xattr handler Andreas Gruenbacher <agruenba@redhat.com> - 2015-10-16 17:30 +0200
  [PATCH v11 43/48] sunrpc: Add xdr_init_encode_pages Andreas Gruenbacher <agruenba@redhat.com> - 2015-10-16 17:30 +0200
  [PATCH v11 28/48] richacl: Set the owner permissions to the owner mask Andreas Gruenbacher <agruenba@redhat.com> - 2015-10-16 17:30 +0200
  [PATCH v11 36/48] nfsd: Add support for the v4.1 dacl attribute Andreas Gruenbacher <agruenba@redhat.com> - 2015-10-16 17:30 +0200
  [PATCH v11 35/48] nfsd: Add richacl support Andreas Gruenbacher <agruenba@redhat.com> - 2015-10-16 17:30 +0200
  [PATCH v11 13/48] richacl: Update the file masks in chmod() Andreas Gruenbacher <agruenba@redhat.com> - 2015-10-16 17:30 +0200
  [PATCH v11 30/48] richacl: Isolate the owner and group classes Andreas Gruenbacher <agruenba@redhat.com> - 2015-10-16 17:30 +0200
  [PATCH v11 20/48] ext4: Add richacl support Andreas Gruenbacher <agruenba@redhat.com> - 2015-10-16 17:30 +0200
  [PATCH v11 27/48] richacl: Propagate everyone@ permissions to other aces Andreas Gruenbacher <agruenba@redhat.com> - 2015-10-16 17:30 +0200
  [PATCH v11 40/48] ext4: Don't allow unmapped identifiers in richacls Andreas Gruenbacher <agruenba@redhat.com> - 2015-10-16 17:40 +0200
  [PATCH v11 26/48] richacl: Move everyone@ aces down the acl Andreas Gruenbacher <agruenba@redhat.com> - 2015-10-16 17:50 +0200
  [PATCH v11 33/48] nfsd: Keep list of acls to dispose of in compoundargs Andreas Gruenbacher <agruenba@redhat.com> - 2015-10-16 17:50 +0200
  [PATCH v11 32/48] richacl: Create richacl from mode values Andreas Gruenbacher <agruenba@redhat.com> - 2015-10-16 17:50 +0200
  [PATCH v11 34/48] nfsd: Use richacls as internal acl representation Andreas Gruenbacher <agruenba@redhat.com> - 2015-10-16 17:50 +0200
  [PATCH v11 15/48] richacl: Create-time inheritance Andreas Gruenbacher <agruenba@redhat.com> - 2015-10-16 18:00 +0200
  [PATCH v11 17/48] richacl: xattr mapping functions Andreas Gruenbacher <agruenba@redhat.com> - 2015-10-16 18:00 +0200
  [PATCH v11 14/48] richacl: Check if an acl is equivalent to a file mode Andreas Gruenbacher <agruenba@redhat.com> - 2015-10-16 18:10 +0200
  [PATCH v11 09/48] richacl: Permission check algorithm Andreas Gruenbacher <agruenba@redhat.com> - 2015-10-16 18:10 +0200

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