Some overlayfs optional features are incompatible with offline changes to the lower tree[1][2][3] and may result in -EXDEV[4], -EIO[5], or other errors. Such modification is not supported and the error behavior is intentionally not specified. Update the "Changes to underlying filesystems" section to note this restriction. Move the paragraph describing the offline behavior below the online behavior so it is adjacent to the following 3 paragraphs describing the NFS export offline modification behavior. [1]: https://lore.kernel.org/linux-unionfs/20200708142353.GA103536@xxxxxxxxxx/ [2]: https://lore.kernel.org/linux-unionfs/CAOQ4uxi23Zsmfb4rCed1n=On0NNA5KZD74jjjeyz+et32sk-gg@xxxxxxxxxxxxxx/ [3]: https://lore.kernel.org/linux-unionfs/20200817135651.GA637139@xxxxxxxxxx/ [4]: https://lore.kernel.org/linux-unionfs/20200709153616.GE150543@xxxxxxxxxx/ [5]: https://lore.kernel.org/linux-unionfs/20200812135529.GA122370@kevinolos/ Signed-off-by: Kevin Locke <kevin@xxxxxxxxxxxxxxx> --- This patch is based on the overlayfs-devel branch of https://github.com/amir73il/linux.git If there is a more suitable base, let me know and I'll rebase the next version. It appears that Vivek's patch[4] has not been applied and serves a similar purpose to this patch, although it applies to a different section of the docs. I'd be happy to collaborate on a combined patch, if there's any interest/need. This patch does not mention nfs_export being incompatible with offline changes to lower, since the following 3 paragraphs specify the behavior (IIUC). If the behavior of offline modification with nfs_export is undefined, should these paragraphs be removed? Thanks for considering, Kevin Documentation/filesystems/overlayfs.rst | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-) diff --git a/Documentation/filesystems/overlayfs.rst b/Documentation/filesystems/overlayfs.rst index fcda5d6ba9ac..9b39374afdbd 100644 --- a/Documentation/filesystems/overlayfs.rst +++ b/Documentation/filesystems/overlayfs.rst @@ -467,14 +467,18 @@ summarized in the `Inode properties`_ table above. Changes to underlying filesystems --------------------------------- -Offline changes, when the overlay is not mounted, are allowed to either -the upper or the lower trees. - Changes to the underlying filesystems while part of a mounted overlay filesystem are not allowed. If the underlying filesystem is changed, the behavior of the overlay is undefined, though it will not result in a crash or deadlock. +Offline changes, when the overlay is not mounted, are allowed to the +upper tree. Offline changes to the lower tree are only allowed if the +"metadata only copy up", "inode index", and "redirect_dir" features +have not been used. If the lower tree is modified and any of these +features has been used, the behavior of the overlay is undefined, +though it will not result in a crash or deadlock. + When the overlay NFS export feature is enabled, overlay filesystems behavior on offline changes of the underlying lower layer is different than the behavior when NFS export is disabled. -- 2.28.0
