Hi, 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. I have not tested it though. So here are very crude RFC patch. I have done bare minimal testing on these and there are many unaddressed issues I can see. Before I go any further, I wanted to send these out for some feedback and see if I am moving in right direction or this appraoch is completely broken. Basically, I am relying on storing OVL_XATTR_ORIGIN in upper inode during copy up. I use that information to get to lower inode later and do data copy up when necessary. I also store OVL_XATTR_METACOPY in upper inode to mark that only metadata has been copied up and data copy up still might be required. Any feedback is helpful. Thanks Vivek Vivek Goyal (7): Create origin xattr on copy up for all files ovl: During copy up, first copy up metadata and then data ovl: Copy up only metadata during copy up where it makes sense ovl: Set xattr OVL_XATTR_METACOPY on upper file ovl: Set OVL_METACOPY flag during ovl_lookup() ovl: Return lower dentry if only metadata copy up took place ovl: Fix ovl_getattr() to get size from lower fs/overlayfs/copy_up.c | 87 +++++++++++++++++++++++++++++++++++++----------- fs/overlayfs/inode.c | 13 +++++++- fs/overlayfs/namei.c | 34 +++++++++++++++++++ fs/overlayfs/overlayfs.h | 5 ++- fs/overlayfs/super.c | 4 +++ fs/overlayfs/util.c | 21 ++++++++++-- 6 files changed, 140 insertions(+), 24 deletions(-) -- 2.13.5 -- To unsubscribe from this list: send the line "unsubscribe linux-unionfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
