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Diffstat (limited to 'Documentation/filesystems/overlayfs.rst')
| -rw-r--r-- | Documentation/filesystems/overlayfs.rst | 19 |
1 files changed, 17 insertions, 2 deletions
diff --git a/Documentation/filesystems/overlayfs.rst b/Documentation/filesystems/overlayfs.rst index eb846518e6ac..16c35b491dad 100644 --- a/Documentation/filesystems/overlayfs.rst +++ b/Documentation/filesystems/overlayfs.rst @@ -123,8 +123,7 @@ At mount time, the two directories given as mount options "lowerdir" and mount -t overlay overlay -olowerdir=/lower,upperdir=/upper,\ workdir=/work /merged -The "workdir" needs to be an empty directory on the same filesystem -as upperdir. +The "workdir" needs to be a directory on the same filesystem as upperdir. Then whenever a lookup is requested in such a merged directory, the lookup is performed in each actual directory and the combined result @@ -347,6 +346,22 @@ The resulting access permissions should be the same. The difference is in the time of copy (on-demand vs. up-front). +Idmapped mounts +--------------- + +The overlay mount itself can be turned into an idmapped mount by applying an +idmapping to it with mount_setattr(2) and MOUNT_ATTR_IDMAP, just like for +other filesystems that support idmapped mounts. + +The mount idmapping only changes how ownership and permissions of the overlay +inodes are presented to and interpreted for the caller. It does not change +how overlayfs accesses the underlying layers: those are still accessed with +the stashed mounter's credentials through their own mounts, which may +themselves be idmapped. The overlay mount idmapping and any layer idmapping +compose, an underlying id is first mapped according to the relevant layer +idmapping and then according to the overlay mount idmapping. + + Multiple lower layers --------------------- |