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From: Miklos Szeredi <>
To: Amir Goldstein <>
Cc: Chengguang Xu <>,
	overlayfs <>
Subject: Re: [PATCH] ovl: consistent behavior for immutable/append-only inodes
Date: Tue, 8 Jun 2021 15:52:32 +0200	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

On Sun, 6 Jun 2021 at 16:46, Amir Goldstein <> wrote:
> When a lower file has immutable/append-only attributes, the behavior of
> overlayfs post copy up is inconsistent.
> Immediattely after copy up, ovl inode still has the S_IMMUTABLE/S_APPEND
> inode flags copied from lower inode, so vfs code still treats the ovl
> inode as immutable/append-only.  After ovl inode evict or mount cycle,
> the ovl inode does not have these inode flags anymore.
> We cannot copy up the immutable and append-only fileattr flags, because
> immutable/append-only inodes cannot be linked and because overlayfs will
> not be able to set overlay.* xattr on the upper inodes.


> Instead, if any of the fileattr flags of interest exist on the lower
> inode, we set an xattr overlay.xflags on the upper inode as an indication
> to merge the origin inode fileattr flags on lookup.
> This gives consistent behavior post copy up regardless of inode eviction
> from cache.
> When user sets new fileattr flags, we break the connection with the
> origin fileattr by removing the overlay.xflags xattr.
> Note that having the S_IMMUTABLE/S_APPEND on the ovl inode does not
> provide the same level of protection as setting those flags on the real
> upper inode, because some filesystem check those flags internally in
> addition or instead of the vfs checks (e.g. btrfs_may_delete()), but
> that is the way it has always been for overlayfs.

That's fine, underlying filesystem is just a backing store.

> As can be seen in the comment above ovl_check_origin_xflags(), the
> "xflags merge" feature is designed to solve other non-standard behavior
> issues related to immutable directories and hardlinks in the future, but
> this commit does not bother to fix those cases because those are corner
> cases that are probably not so important to fix.
> A word about the design decision to merge the origin and upper xflags -
> Because we do not copy up fileattr and because fileattr_set breaks the
> link to origin xflags, the only cases where origin and upper inodes both
> have xflags is if upper inode was modified not via overlayfs or if the
> system crashed during ovl_fileattr_set() before removing the
> overlay.xflags xattr.  In both cases, modifiying the upper inode is not
> going to be permitted, so it is better to reflect this in the overlay
> inode flags.

So why not implement the non-merge (#3) behavior unconditionally?
That would solve all issues related to fileattr, right?


  reply	other threads:[~2021-06-08 13:52 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-06-06 14:46 [PATCH] ovl: consistent behavior for immutable/append-only inodes Amir Goldstein
2021-06-08 13:52 ` Miklos Szeredi [this message]
2021-06-08 14:37   ` Amir Goldstein
2021-06-08 14:49     ` Miklos Szeredi
2021-06-08 15:33       ` Amir Goldstein
2021-06-08 18:20         ` Miklos Szeredi
2021-06-09  6:08           ` Amir Goldstein
2021-06-09  7:28             ` Miklos Szeredi
2021-06-09  7:57               ` Amir Goldstein
2021-06-11  7:31                 ` Amir Goldstein
2021-06-11  7:55                   ` Miklos Szeredi
2021-06-11  8:37                     ` Amir Goldstein
2021-06-11  8:39                       ` Miklos Szeredi

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