In one of the recent converstions, people mentioned that chown/chmod lead to copy up files as well as data. We could optimize it so that only metadata is copied up during chown/chmod and data is copied up when file is opened for WRITE. This optimization potentially could be useful with containers and user namespaces. In popular scenario, people end up doing chown() on whole image directory tree based on container mappings. And this chown copies up everything, breaking sharing of page cache between containers. With these patches, only metadat is copied up during chown() and if file is opened for READ, d_real() returns lower dentry/inode. That way, different containers can still continue to use page cache. That's the use case I have in mind. --- Vivek Goyal (28): ovl: Initialize ovl_inode->redirect in ovl_get_inode() ovl: Move the copy up helpers to copy_up.c ovl: Provide a mount option metacopy=on/off for metadata copyup ovl: During copy up, first copy up metadata and then data ovl: Copy up only metadata during copy up where it makes sense ovl: Add helper ovl_already_copied_up() ovl: A new xattr OVL_XATTR_METACOPY for file on upper ovl: Use out_err instead of out_nomem ovl: Modify ovl_lookup() and friends to lookup metacopy dentry ovl: Copy up meta inode data from lowest data inode ovl: Add helper ovl_dentry_lowerdata() to get lower data dentry ovl: Fix ovl_getattr() to get number of blocks from lower ovl: Store lower data inode in ovl_inode ovl: Add helper ovl_inode_realdata() ovl: Open file with data except for the case of fsync ovl: Do not expose metacopy only dentry from d_real() ovl: Move some dir related ovl_lookup_single() code in else block ovl: Check redirects for metacopy files ovl: Treat metacopy dentries as type OVL_PATH_MERGE ovl: Add an inode flag OVL_CONST_INO ovl: Do not set dentry type ORIGIN for broken hardlinks ovl: Set redirect on metacopy files upon rename ovl: Set redirect on upper inode when it is linked ovl: Check redirect on index as well ovl: Disbale metacopy for MAP_SHARED mmap() ovl: Do not do metadata only copy-up for truncate operation ovl: Do not do metacopy only for ioctl modifying file attr ovl: Enable metadata only feature Documentation/filesystems/overlayfs.txt | 30 +++- fs/overlayfs/Kconfig | 19 +++ fs/overlayfs/copy_up.c | 160 ++++++++++++++++----- fs/overlayfs/dir.c | 74 +++++++--- fs/overlayfs/export.c | 3 + fs/overlayfs/file.c | 43 ++++-- fs/overlayfs/inode.c | 112 +++++++++------ fs/overlayfs/namei.c | 195 ++++++++++++++++---------- fs/overlayfs/overlayfs.h | 33 ++++- fs/overlayfs/ovl_entry.h | 6 +- fs/overlayfs/super.c | 62 +++++++- fs/overlayfs/util.c | 241 +++++++++++++++++++++++++++++++- 12 files changed, 780 insertions(+), 198 deletions(-) -- 2.14.3
